Consequences of age at weaning and postweaning feeding regime on the production
performance of beef bulls.
MSc Thesis
Clementina Álvarez
Supervisor: Mogens Vestergaard
Department of Animal Science: Animal Nutrition and Physiology
Aarhus University-Foulum
2016
TABLE OF CONTENTS
1.
INTRODUCTION ................................................................................................................... 1
2.
BACKGROUND OF THE STUDY ........................................................................................ 4
2.1.
WEANING AGE .............................................................................................................. 4
2.2.
FEEDING STRATEGIES .............................................................................................. 11
3.
OBJECTIVES AND HYPOTHESIS .................................................................................... 22
4.
MATERIALS AND METHODS .......................................................................................... 24
5.
6.
4.1.
STUDY SITE AND DATES .......................................................................................... 24
4.2.
ANIMALS AND MANAGEMENT ............................................................................... 24
4.3.
HOUSING ...................................................................................................................... 25
4.4.
TREATMENTS AND DIETS ........................................................................................ 27
4.5.
SLAUGHTER ................................................................................................................. 30
4.6.
MEASUREMENTS ........................................................................................................ 31
4.7.
CALCULATIONS .......................................................................................................... 31
4.8.
STATISTICAL ANALYSIS .......................................................................................... 32
RESULTS .............................................................................................................................. 34
5.1.
GROWTH RATES AND LIVE WEIGHTS. ................................................................. 34
5.2.
FEED INTAKE, FEED EFFICIENCY AND DAYS AT FEED.................................... 36
5.3.
CARCASS QUALITY AND TRAITS ........................................................................... 41
DISCUSSION........................................................................................................................ 42
6.1.
GROWTH RATE AND BODY WEIGHTS .................................................................. 42
6.2.
FEED INTAKE AND EFFICIENCY ............................................................................. 48
i
6.3.
CARCASS CHARACTERISTICS ................................................................................. 52
7.
CONCLUSIONS AND PERSPECTIVES. ........................................................................... 53
8.
SUMMARY .......................................................................................................................... 54
9.
ACKNOWLEDGEMENTS .................................................................................................. 55
10. REFERENCES ...................................................................................................................... 56
ii
LIST OF TABLES
Table 1: Compilation of studies comparing ADG of Early weaning (EW) versus Normal
Weaning (NW)*. ............................................................................................................................. 6
Table 2: Milk production of cows from different breeds during lactation (kg milk), 1-182
days (Adapted from Olesen et al. (2004))* ..................................................................................... 6
Table 3: Compilation of studies on the effect of TMR on total, silage and concentrate
intake and ADG on beef cattle. ..................................................................................................... 18
Table 4: Description of the blocks representing a breed in the two years of the study. ................ 25
Table 5: Nutrient composition and ingredients of the concentrate diets. ...................................... 29
Table 6: Silages used in TMR and SEP feeding per period. ......................................................... 29
Table 7: Nutrient composition of the silages used in the study. .................................................... 30
Table 8: Slaughter weight depending on Fat score criteria of each breed ..................................... 31
Table 9: LSM and SEM for growth rates, weight and age at slaughter of the bulls in
different periods of the study. ........................................................................................................ 34
Table 10: LSM and SEM for daily intake of concentrate, silage, total, digestible crude
protein and feed efficiencies of the bulls in the period from 6 months of age to slaughter. ......... 38
Table 11: LSM and SEM for daily intake of concentrate, silage, total, digestible crude
protein, feed efficiencies and days on feed of the bulls in the period from weaning age to
slaughter. ....................................................................................................................................... 39
Table 12: LSM and SEM for carcass characteristics..................................................................... 41
Table 13: Growth rates calculation for the period between weaning dates (EW-NW) ................. 43
iii
LIST OF FIGURES
Figure 1: Evolution of the number of suckling cows and number of farms with sucking
cows in Demark (2005-1015) (Adapted from Statistics Denmark, 2015)... .................................... 1
Figure 2: Live weight of EW (weaned at 90 days) and NW (weaned at 180 days) thourgh
the production cycle (Blanco et al., 2008). ...................................................................................... 9
Figure 3: Monthly gains of EW and NW calves during the finishing phase (both groups
already weaned) (Blanco et al., 2008). .......................................................................................... 10
Figure 4: Effect of the feeding method on the monthly live weight of beef heifers. (Casasús
et al., 2012) .................................................................................................................................... 19
Figure 5: Effect of the feeding method on the monthly intake relative to the live weight (g
DM/kg LV). ................................................................................................................................... 20
Figure 6: Typical course of pH in the rumen in relation to the feeding frequency
(Kaufmann, 1976).......................................................................................................................... 21
Figure 7: Feeding stations in each pen .......................................................................................... 26
Figure 8: Frost-proof water cups in the pens ................................................................................. 26
Figure 9: Pens used in the study for the bulls ................................................................................ 26
Figure 10: Automatic recorder used in the feeding stations. ......................................................... 30
Figure 11: Concentrate and silage intake as feed units (SFU/day) of bulls from the period
from weaning to slaughter.* .......................................................................................................... 40
Figure 12: Body weight at weaning for EW (3 months weight) and NW (6 months weight)....... 44
Figure 13: Growth rates of EW and NW bulls from weaning to slaughter divided in subperiods. .......................................................................................................................................... 45
iv
Figure 14: Live weight evolution of EW and NW from 90 days old (EW weaning date) to
slaughter. ....................................................................................................................................... 47
Figure 15: Records of the feeding pattern of an EW-SEP bull. .................................................... 49
Figure 16: Records of the feeding pattern of an NW-SEP bull. .................................................... 50
Figure 17: Records of the feeding pattern of an NW-TMR bull. .................................................. 50
Figure 18: Silage, concentrate, straw and total intake for the six treatments of the study in
the overall period. .......................................................................................................................... 51
v
ABBREVIATION KEY
ADG= Average daily gain
Ca= Calcium
CA= Clementina Álvarez
CONC= Concentrate diet
CP= Crude Protein
DKC= Danish Cattle Research Centre
DM= Dry matter
DMI= Dry matter intake
EW= Early Weaning
FCE= Feed Conversion Efficiency
G=F= Gain to feed ratio
LW= live weight
Mg= magnesium
NDF= Non-digestible fiber
NEI= Net Energy Intake
NW= Normal weaning
P= Phosphorus
SEP= Separate feeding
SFU= Scandinavian Feed Units
TMR= Total mixed ration
UFV= Unité Fourragère Viande
WxF= Weaning and Feeding interaction
vi
1. INTRODUCTION
Denmark bases it beef production on a suckling-calf system. The system uses bull calves,
performing weaning at approximately 6 months of age. After weaning, the conventional fattening
phase is completed on indoor feedlot, with a diet consisting of large amounts of concentrate.
Bulls are usually slaughtered at 12 months of age with 450 kg of live weight (Nielsen and
Thamsborg, 2005). Bulls are chosen over steers because of their higher growth potential
and better feed conversion ratio (Andersen and Ingvartsen, 1984, Steen, 1995), which makes
them more suitable for this intensive system, based on short life cycles with high growth rates.
Despite the intensive system, beef production in Denmark is relatively small. This can be seen on
Figure 1 by analyzing the herd size of suckling cows and farms. The suckling cow is used to
explain the beef production system as the cow is the foundation unit of the production by
providing the bull calves. The number of suckling cows has dropped 10,000 heads in the last
decade. A drop has also being registered of farms containing suckling cows, reducing their
number by 1500 farms in a decade (Statistics Denmark, 2015). However, the average size of the
farms had few variations over the years, registering an average herd size of 11.9 suckling cows
per farm.
Figure 1: Evolution of the number of suckling cows and number of farms with sucking cows in
Demark (2005-1015) (Adapted from Statistics Denmark, 2015).
1
Despite the small production type, after dairy cows, young bulls are the main product of export of
bovine meat, mainly to Germany, Italy and Spain (Agriculture and Food Council,
2013). Additionally, cull cows meat quality has a lot of variation as their slaughter criteria
bases on the milk production yield, so their age and degree of finishing at slaughter differs
widely (Niels and Thamsborg, 2002). Therefore, young bulls are the main source of
Danish quality beef. Furthermore, beef is also important for the local market, at it
comprises 30% of the total meat consumption of a Danish person (Agriculture and Food
Council, 2013).
Within several ways to improve this type of production, early weaning is a popular tool. Several
authors indicate this tool as an easy way to take advantage of the high growth rates potential with
lower intakes of the calves (Robelin and Tulloh, 1992). This would allow reducing the need of
high daily growth rates during the fattening period while achieving the same slaughter weights
with suitable carcass quality. Another possibility would be reducing the age at slaughter by
maintaining high growth rates throughout the whole period. However, some studies showed that
later weaned calves would have higher rates on the last fattening period due to
compensatory growth, making early weaning meaningless (Blanco et al., 2008). Despite the
disagreement on the performance of the calf, it is well documented that early weaning influences
positively the reproductive performance of the dam, as interrupting the milk production would
reduce the energy requirements of the cow and allow more recovery time for the next breeding
season. Several studies showed an increase in body weight and body score as compared to cows
raising their claves for a longer period, resulting on an increase of the pregnancy rate on the next
season (Myers et al., 1999a, Myers et al., 1999b, Grimes and Turner, 1991a, Peterson et al., 1987,
Story et al., 2000). This would be especially important for dams with low energy supply, like
marginal pasture grazing in Danish farms. Moreover, Robison et al. (1978) showed that the milk
production of the dam is not enough to meet the requirements of the calf after one month
lactation, so early weaning will be an appropriate tool for meeting the calves requirements
through feed. However, early weaning has been studied mainly in steers and not bulls, so few
information is available to adjust the Danish beef farm systems.
Another aspect to take into consideration in this intensive production system is the type of diets
used after weaning. The fattening system based on grains, oil seeds and protein sources involves
2
higher costs than silage-based diets. Moreover, it can be a major problem on metabolic and
feeding related disorders to the bull. Vestergaard et al. (2003) stated that concentrates supplied ad
libitum for young bulls had high risk of ruminal acidosis. Kjeldsen and Fisker (2002)
found, from Danish slaughterhouse data records, that 11% of the slaughter young bulls in
Danish slaughterhouses presented liver absence, consequence of sub-clinical acidosis. In
intensive and small-scale production systems, the loss of one animal or the low performance
will have a great effect on the economy of the farm, as there is high investment on each
animal. For this, it is important to consider if more a balanced feeding method, including
roughage can adapt to the high growth rates system.
Therefore, there is a need to evaluate if early weaning together with diets that include high
quality roughage can be suitable for the Danish young bull production.
3
2. BACKGROUND OF THE STUDY
2.1. WEANING AGE
In this chapter, the effect of early weaning on beef production from previous studies will be
discussed. As mentioned before, it is agreed that, from the dam perspective, early weaning
brings positive results. However, the results on calf performance are not as clear and therefore
being the focus of our study. Growth, feed intake, efficiency and the final carcass
quality will be reviewed in this section in order to give the reader an overall view of previous
results.
2.1.1. Growth
Studies comparing daily gains between early weaning (EW) and normal weaning calves (NW)
are shown in Table 1. Average daily gain (ADG) was analyzed in 3 periods for all the studies.
The first period, from the date of early weaning until the date for normal weaning (EW-NW),
which intends to compare if there is difference in ADG of the calves early weaned compared to the
ones that remain with their dams. The second period is from NW age to slaughter, comparing the
ADG of both groups after being separated from their dams (although EW was separated earlier).
Finally, the column on the right describes the ADG during the whole period, taking into account
both periods described before. Table 1 shows that all studies agree that EW increased ADG
comparing to calves that are still with their dams, resulting in heavier animals at the time of
normal weaning. Despite this overall agreement, studies differed in the magnitude of the ADG.
This can be explained by the different experimental conditions under which the results were
obtained. For example, Kubisch and Makarechian (1987) registered the lowest gains of the
compiled studies explained by the authors by high influence of the low temperatures and snow of
the year in which the experiment was carried out. This affected milk yield of the dams and animal
performance, as they were autumn-borne calves, weaned at the beginning of winter. Grimes and
Turner (1991a) also registered low ADG, 0.68 and 0.5 kg/day for EW and NW
respectively, explained because it was a grazing-based system, where EW after being
separated from their dams where kept on grazing having a target ADG between 0.68 and 0.9 kg/
day.
4
On the other hand, Schoonmaker et al. (2001) recorded high ADG for both weaning ages,
EW due to grain-based diets while NW received high quality pasture together with the fact it
was summer season, so conditions were mild. In addition, calves were implanted with
hormones, which more gains are expected. Another factor affecting the performance of NW
compared to EW could be explain by the milk production of the dam and nutrient supply
that comes from other sources, like pasture accessibility to the suckling calf (Lusby et al.,
1981). Coinciding with this, Abdelsamei et al. (2005) found higher pre-weaning ADG of
calves coming from dams with higher milk production. Moreover, milk production can be
affected by the feed intake and feed quality of the dam, but also t h e breed of the dam
plays a vital role as supported by Olesen et al. (2004) in Table 2. Simmental cows had
higher milk production potential as compared with Limousine and Hereford. Conversely,
the milk production can be significantly affected by the feeding level, as Simmental cows
in a low feeding regime produced less milk than a Hereford in a high feeding regime.
5
Table 1: Compilation of studies comparing ADG of Early weaning (EW) versus Normal Weaning
(NW)*.
Average daily gain (kg/day)
Study characteristics
1
2
3
EW-NW
NW-S
EW-S
Author
Breed
G
EW vs NW
(days)
A cb
S
103 vs 203
1.3
0.8
1.5
1.5
1.4
1.3
Fluharty et al. (2000)
SxAxH
S
90 vs 215
1.6
0.7
1.1
1.2
1.2
1.0
Myers et al. (1999b)
A; A cb
PM and
P
S
100 vs 200
1.3
0.9
1.3
1.4
1.3
1.2
Barker-Neef et al. (2001)
B
90 vs 150
1.3
0.7
1.6
1.7
1.5
1.4
Blanco et al. (2009)
B
157 vs 189
0.3
0.1
1.6
1.8
1.2
1.3
S
110 vs 220
0.7
0.5
1.3
1.2
1.1
1.0
B
90 vs 180
1.6
0.8
1.3
1.8
1.4
1.2
Kubisch and Makarechian
(1987)
Grimes and Turner (1991a),
Grimes and Turner (1991b)
Blanco et al. (2008)
S
150 vs 210
1.5
1.1
1.3
1.4
1.4
1.3
Story et al. (2000)
S
119 vs 204
S
108 vs 202
S.
AxS
133 vs 233
H
Overall Mean6
1.5
1.6
0.9
1.0
1.6
1.6
1.7
1.8
1.6
1.6
1.4
1.5
Schoonmaker et al. (2004)
1.6
1.2
1.5
1.6
1.5
1.5
Meteer et al. (2013)
1.2
0.8
1.4
1.5
1.4
1.3
4
Sy
ShxAx
H
PM
AxHxS
xG
AxS
AxS
5
E
W
N
W
E
W
NW
EW
NW
Schoonmaker et al. (2001)
*Bold font numbers significantly different ADG in the studies. Italic font corresponds to the ADG calculated by CA from partial
ADG of both periods. 1Period from date of early weaning to normal weaning date; 2Period from normal weaning date to
slaughter; 3Period from early weaning to slaughter; 4Angus (A), Simmental (S), Hereford (H), Parda de Montania (PM),
Pireniaca (P), Gelbvieh (G), Synthetic (Sy), cb: crossbreed. 5Gender (G), Steers (S), Bull (B), Heifers (H). 6Overall mean
calculated by CA.
Table 2: Milk production of cows from different breeds during lactation (kg milk), 1-182 days
(Adapted from Olesen et al. (2004))*
Breed
Simmental
Hereford
Limousine
P value
Dam Energy level
High
Low
energy
energy
2434
1366
1662
1072
1378
1264
<0.001
<0.001
*Values are a calculated average of two lactating periods evaluated in the study
The period from NW to slaughter, the results from the 11 studies shown in Table 1 were
not as consistent, having two main tendencies. On one hand, some studies stated that there is
no effect of the weaning age on post weaning gains (Fluharty et al., 2000, Myers et al., 1999b,
6
Barker-Neef et al., 2001, Blanco et al., 2009, Kubisch and Makarechian, 1987, Schoonmaker et
al., 2004). On the other hand, other studies showed that NW had higher ADG post
weaning, displaying compensatory growth, due to the pre-weaning restriction (Blanco et
al., 2008, Story et al., 2000, Schoonmaker et al., 2001, Meteer et al., 2013). However, in
all cases it is clear that NW gains increase post weaning compared to their own previous
period while there is no clear tendency of this for EW.
Whatever the post-weaning tendency is, when the overall ADG was evaluated across these
studies or calculated by CA out of partial ADG, it is clear that EW had higher ADG than NW
in the whole study period (EW to S), although some results may not be significantly different.
2.1.2. Feed intake and feed efficiency
Fluharty et al. (2000) showed that the overall daily dry matter intake (DMI) on the finishing
period was no different between weaning ages, recording 8.7 and 8.8 kg DM/day respectively.
When comparing total DMI, it was significantly higher for NW as they spent 34 more days in the
feedlot because of lower ADG (Table 1) in order to reach the desired slaughter weight. Feed
efficiency was 5% higher for EW calves (0.176 vs 0.167 kg gain/kg feed respectively). These
results agree partially with Myers et al. (1999b) which also stated that there is a better feed
efficiency as weaning age increases because daily DMI increases significantly for later weaned
animals. However, the authors also stated that the total intake of concentrate increased with
earlier weaning age, as EW spent more days in the feedlot. The difference in total feed intake
between both studies may be attributed to the difference in slaughter criteria, as days on the
feedlot increases for EW when the slaughter is at a constant fat-end point or same age. This is in
accordance with Blanco et al. (2008)¸Story et al. (2000) and Meyer et al. (2005). However,
Barker-Neef et al. (2001) slaughtering steers at the same fat end point, stated that although EW
had 40 more days at feed due to earlier weaning, they still consumed 81.5 kg less total DM than
NW. This was explained due to EW having higher ADG (Table 1) and lower daily DMI (5.95 vs.
7.40 kg DM/day), resulting in higher feed efficiency for EW (0.24 vs. 0.19 kg gain/kg feed).
7
Disagreeing with those findings, Greenwood and Cafe (2007) reviewing earlier studies concluded
that there were no clear findings that feed efficiency was affected by weaning age when slaughter
target is a constant age or weight. This agrees with Waterman et al. (2012) and Pritchard et al.
(1988).
It seems that overall DMI is influenced by the number of days on feed and slaughter criteria
rather than the feed efficiency.
2.1.3. Slaughter
When slaughtered at a similar fat-end point most studies confirm that EW were younger and
lighter at slaughter (Schoonmaker et al., 2004, Grimes and Turner, 1991b). Agreeing with this,
Barker-Neef et al. (2001) explained these results by stating that EW calves fed with high energy
level diets will promote fat deposition earlier, having lighter slaughter weights. This means that if
managed the same way during the finishing period EW harvest carcasses will be fatter at an
earlier age (Waterman et al., 2012).
When slaughtered at a fix live weight (LW), the difference is also clear. Blanco et al. (2009)
showed EW calves were 17 days younger than traditional weaned when slaughtered at 450 kg of
live weight, coinciding with Schoonmaker et al. (2001). Moreover, Fluharty et al. (2000) stated
that market slaughter weight was reached by EW 34 days earlier, due to the higher gains, as this
weaning tool means earlier access to feed while NW are still with their dams.
When the slaughter at a fix age, it is clear that EW will spend more days on feed as they are
weaned at an earlier age. Meyer et al. (2005) found no difference in LW at 370 days of age for
EW and NW weaned at 60 and 174 days, respectively. Higher ADG of NW animals explained this
result in the feedlot period, although EW spent 112 days more on feed. As seen on Figure 2,
Blanco et al. (2008) agrees with these results, as EW where heavier at the time of normal
weaning (180 days), but after NW reached the same weight at the end of the experimental period.
This was explained by a difference in growth rates in the fattening phase (from 180 days to
8
slaughter) between weaning strategies. EW group showed higher growth rates for the first 30
days of this period because the adaptation of the NW calves to the feed at the beginning did not
allowed higher ADG. After, NW had higher ADG for 90 days, allowing the same slaughter
weight (Figure 3). This was explained by the authors due to lower maintenance requirements due
to lower body weight (80 kg lighter) when entering the finishing phase of the feedlot, allowing
more energy available for growth.
However, both of these studies showed compensatory growth, which is not the common tendency
of other studies defining different slaughter criteria. Pritchard et al. (1988) comparing two
weaning periods slaughtered at two different ages also found no difference in slaughter weight in
neither ages between weaning treatments. ADG did not vary in the feedlot but NW had very good
gains during their pre-weaning time, due to excellent pasture conditions.
Within a day *** differ P<0.001 and ** at P<0.01
Figure 2: Live weight of EW (weaned at 90 days) and NW (weaned at 180 days) through the
production cycle (Blanco et al., 2008).
9
Within a day *** differ P<0.001 and ** at P<0.01
Figure 3: Monthly gains of EW and NW calves during the finishing phase (both groups already
weaned) (Blanco et al., 2008).
2.1.4. Carcass characteristics
Previous studies came to different conclusions for carcass characteristics. Most studies agree that
the effect is limited, as only carcass conformation score improved in early weaners (Blanco et al.,
2009), or no effect of weaning age was detected on the carcass weight, conformation nor fat
scores (Fluharty et al., 2000, Kubisch and Makarechian, 1987, Arthington et al., 2005, Thompson
et al., 2009, Schoonmaker et al., 2001, Myers et al., 1999b, Pritchard et al., 1988).
Others studies found differences between weaning strategies but their findings were not
consistent between them. Some found heavier carcass for NW as a result of higher slaughter
weight and higher dressing percentage when target was a constant back fat thickness (BarkerNeef et al., 2001). Grimes and Turner (1991b) also found higher dressing percentage for NW but
hot carcasses were lighter.
10
When slaughtered at the same age it seems that results depend on the aging target as result of the
tissue development of the animal. When slaughtered at 1 year old, with similar slaughter weight
EW carcass were heavier (Meyer et al., 2005, Blanco et al., 2008) and was explained by higher
dressing percentage with no differences in conformation or fat score. However, when animals
were slaughtered at 30 months of age with different pre-weaning ADG, EW had heavier
carcasses due to higher pre-weaning growth rate but they were also fatter (Greenwood and Cafe,
2007). When comparing at same carcass weight (380 kg) the same authors also found higher fat
percentage, leading on a lower retail yield. This agrees with Waterman et al. (2012)., when the
slaughter target age was as high as 500 days, although hot carcass weight was higher in EW it
had lower dressing percentage compared to NW.
From this, we can conclude that EW will have higher growth rates while NW are still with their
dams. However, after normal weaning is performed up to slaughter, it is not clear if NW will
compensate their lack of growth achieving the same LW by the end of the feedlot period. This
will also depend on the slaughter criteria (age, LW or fatness). It seems that if the criteria are fatend point EW will reach this goal faster, shortening the production period but carcasses will be
lighter. This effect will clearer when EW are submitted to high concentrate diets, promoting
earlier fat accretion. When slaughter criteria are a target LW, it is possible EW will have fatter
carcasses due to earlier deposition of fat. It is not clear if this will affect the final carcass
conformation and fat score as studies show contrasting results.
2.2. FEEDING STRATEGIES
The cost of feed is the highest expense of beef livestock production (Caplis et al., 2005, Keane et
al., 2006, French et al., 2001). For this, the impact of the feeding system, meaning each
component of the diet and their possible combinations, on animal performance and carcass
quality, is vital to find the most cost efficient way to produce beef without compromising these
aspects. In this section, the effects of the type of diet (concentrate versus silage based diets) and
feeding method (mixed versus separate rations) on beef production will be discussed, as it is vital
for the farm production system.
11
2.2.1. Type of diet: Concentrate versus silage based diets
It is well recorded that concentrate feeding increases animal gains as compared to all forage diets.
In addition, as the quality of the concentrate vary less than with forages, results such as gain and
intake are more predictable with concentrate diets (O'Kiely, 2011). However, grains, oil-seeds
and protein sources in the concentrate part of the diet are expensive components and their prices
had risen in the last years (Casasús et al., 2012). In addition, increasing concentrate in the diets
with less structural carbohydrates can raise the “acidogenetic effect” of the diet (Murphy et al.,
1994), leading to bloats and liver abscesses, reducing overall performance (Jørgensen, 2008).
Therefore, if silage-based diets with the inclusion of concentrate supplementation could
achieve as similar performances on live animal and carcass traits as an all-concentrate feed diet,
it would reduce costs and decrease the potential health problems previously described.
→ Effect on growth rates
Few studies stated that including grass-based diets accompanied by concentrate achieved similar
animal performance than an all-concentrate diet without affecting meat quality. As an example,
French et al. (2001) analyzing Limousin and Charolais steers found that the all-concentrate diets
had higher ADG (1.43 vs 1.14 kg/d) than feeding autumn quality grass plus 5 kg of concentrate.
However, no differences were found on daily carcass gains (809 and 727 g/d), final carcass
weight, kill out proportion or conformation score, agreeing with French et al. (2000). The authors
assumed that if the all-concentrate diet reached the growth potential, by including grass and
concentrate 90% of the growth potential could be reached while having a cheaper diet.
Keane and Allen (1998) feeding Charolais x Friesian 7 months of age bulls also obtained high
ADG with a silage-based diets and 55% concentrate (1.18 kg/day mean in all the period).
Slaughter at 19 months of age, heavy carcasses were obtained (384 kg) with almost 57% of
kill out proportion and with acceptable conformation and fat scores for the industry (3.58 and
3.29 respectively in the EUROP scale). Agnew and Carson (2000) found daily gains of 0.8 kg /d
when grass silage of a perennial prairie was supplemented with 4.5 kg of concentrate on
12
continental crossbreed steers. Huuskonen et al. (2009) found for daily breed heifers raised
for finishing system ADG of 1 kg/day by including 3.5 kg/day DM of rolled barley. Although
conformation score was poor with this diet, the authors attributed this to the dairy breed lean
characteristics.
The differences in magnitude of ADG between these studies can be explained by the breed or
cross used, the differences in the period evaluated or the quality of the silage and concentrate that
was included in the diet. As an example, Huuskonen et al. (2009) had higher daily gains on daily
breed heifers than Agnew and Carson (2000) using crossbred steers. This was probably due to
higher protein content of the silage and that the period evaluated was from early weaning, when
animals have high efficiency rate and high gains while in the latter study the animals were
evaluated only in the finishing period.
Despite the positive results for silage-based diets, Moloney et al. (2008) stated different findings.
Ad libitum concentrate diets had higher overall growth (9.9 vs 7.2 kg/day), significantly
higher LW efficiency in energy terms (10.1 vs 8.3 g/ MJ ME) and higher carcass gain efficiency
(7.0 vs 5.2 g/MJ ME) than feeding silage ad libitum plus 6 kg of concentrate. Keane et al.
(2006) and Caplis et al. (2005) also found maximum live weights with all-concentrate diet
leading to maximum carcass gains and heavier carcass weight with better conformation
and fat score. O'Kiely
concentrate
diet
(2011)
feeding
continental
crossbred
steers
different
silage-
combinations, also found higher DMI for the all concentrate diets than
silage plus 3 kg of concentrate (11.3 vs 9.9 kg/d), having almost double carcass gains with
higher feed efficiency (as DM). At the end of the feeding period, this concluded in heavier
animals and heavier carcasses with more kill out proportion and better conformation. No
significant differences were found in the fat scores, although it was almost 0.5 points higher for
the concentrate diet.
Higher animal performance by feeding an all-concentrate diet agrees with the results shown by
Zea Salgueiro et al. (2009) who recorded 1.37 g/day vs 1.61 kg/d of ADG with grass silage plus 5
kg concentrate versus ad libitum concentrate, respectively. Despite this, no differences in
conformation or fat score where found when slaughtered at a fix weight. Nevertheless, when the
13
all concentrate diet was compared to diets with only 2 kg/day of concentrate, conformation and
fatness score was lower, as well as dressing percentage, coinciding with Andersen and Ingvartsen
(1984) with increasing concentrate proportions.
→ Effect on feed intake
It was previously stated that French et al. (2001) found higher ADG but no differences in carcass
gain for all-concentrate diets compared to grass based diets with 5 kg of concentrate
supplementation. Regarding the daily intake, expressed as kg of DM, it was similar between
feeding strategies, 13.3 and 13.7 kg DM/day respectively. However, the proportions of the
components of this intake differed, as the grass-based diet had most of their intake from the grass
component (10.7 kg DM/day) while all-concentrate had no grass intake. These results, agree with
Caplis et al. (2005) evaluating intake as DM (kg DM) stated that intake was similar when
comparing an all-concentrate diet with a silage diet plus 6 kg DM/day of concentrate daily
allowance (10.31 vs 10.83 kg DM/day, respectively). The author compared the composition of
the total daily intake by evaluating the concentrate proportion of the intake, registering only 45%
concentrate for the silage-based diet, while all-concentrate diet had 85% ratio of concentrate
intake. When the intake was compared in energy terms (UFV/day=Unité Fourragère Viande),
all-concentrate diets will have the highest energy intake compared to the silage-based diet (11.28
vs 10.78 UFV/day, respectively). Similar effect of the concentrate level were indicated by Keane
et al. (2006) using a similar design study as Caplis et al. (2005).
On the other hand, Hironaka et al. (1994) found lower DM and digestible energy (DE)
intake for all-concentrate diets, as their studies showed a quadratic effect, increasing intake up
to a diet which had 65% concentrate and then decreased as the proportion reached 100%.
Nevertheless, the ADG performance did not decrease with all concentrate diets. This led into
higher feed efficiency use with the all-concentrate diets, expressed as both gain per DE and
DM unit. In this case, the relation showed a cubic effect, increasing the efficiency as
concentrate increases with a more significant increase, and maximum, when the diet
consisted in all concentrate. The authors explained these results by the increase of
digestibility of the diets involving only concentrates ad libitum together with the change of the
14
products of digestion. The volatile fatty acid (VFA) proportions change with all concentrates
as compared to diets including forage and concentrates. Regarding VFA proportions, Mould et
al. (1983) feeding different levels of barley to sheep, concluded that with increasing
concentrations of barley in the diet the molar proportion of propionic acid increased in
expense of a decrease of acetic acid. This was independently if the barley was presented as
whole grain or pelleted, having a molar proportion of 48:40:8 of propionic, acetic and
butyric acid in all concentrate diet respectively. Being the main glucogenic precursor in
ruminants, propionate is increasing its efficiency of use for animal production as compared
with acetate. However, also other factors such as energy used for digestion and absorption
also plays an important role, as reviewed by van Houtert (1993) and Dijkstra (1994).
→ Effect on carcass quality
When evaluating carcass quality, most studies above coincide with fatter and better conformation
carcasses with all concentrate diet. Despite this, some studies found no differences in both
characteristics, probably due to the slaughter criteria were a fix LW or targeted same carcass
weight at slaughter. This may lead to the fact that all concentrate diets had better conformation
and fat scores due to higher gains and earlier fat deposition rather than the diet per se.
Dressing percentage expected to increase with all concentrate diets, as the gut fill is one of the
main factors affecting it. So by feeding all concentrate diets, energy concentration increases
lowering the gut content (Zea and Díaz, 1990). This agrees with Keane et al. (2006) and
Andersen and Ingvartsen (1984) .
2.2.2. Feeding Method: Silage based TMR versus separately
The inclusion of silage in the diet also brings up the debate on which is the best way to be
supplied to the animal, separate from the concentrate or included in the same ration as total mixed
rations. Total Mixed Ration (TMR) is the complete mixed of the concentrate and forage
components of the diet, resulting in an homogenous blend (Yan et al., 1998) that can be fed
15
directly. The use of TMR has been widely studied on dairy cattle but there are few studies for
beef cattle. Either cattle group studies do not bring clear conclusions.
The use of TMR has been encouraged over separate for several reasons. First, as a practical
approach for the herd production, as it is easier to handle in production systems by saving labor
and feed handling is mechanized (Keane et al., 2006). However, it requires a mixer-wagon,
which involves a one time high investment, but also maintenance. Secondly, it could improve
animal performance as it may lead to fewer fluctuations of the ruminal pH, as it would
synchronize the fermentable energy:nitrogen supply. Finally, mixing would avoid the
ingestion of high amounts of concentrates right after it is delivered, as is a common case
when concentrates and forage are supplied separately in the day or in the same pen but the
concentrate is top-dressed over the forage part (DeVries and von Keyserlingk, 2009). On
the other hand, separate feeding will disrupt ruminal fermentation pattern and pH when high
concentrates are included in the diet and the feeding times per day are fewer (Yan et al., 1998).
All these reasons would theoretically make TMR increase animal performance as compared to
separate feeding. Nevertheless, when it comes to comparing studies that evaluated both methods
on animal performance the advantages mentioned above are not as clear. As examples, Cooke et
al 2004 found positive results by mixing silage and concentrate compared to presenting them
separately. Daily gains increased for the TMR resulting in higher slaughter and carcass weights.
Moreover, when TMR was compared with an all-concentrate diet, there were no significant
differences on any of the above characteristics between these two diets. On the other hand, Keane
et al. (2006) found no differences between the method of presenting the silage on the diet, and
animal performance was highest with an all-concentrate diet offered ad libitum. These two
studies demonstrate the inconsistent results shown by the literature on the feeding method of
silage-based diets.
This section will try to present the available studies of the feeding method, TMR or separate
feeding, compared for several animal performance variables.
16
→ Effect on intake
Table 3 is a compilation of studies comparing the effect of both feeding methods on DM intake
and ADG. DM intake is also sub-divided into silage and concentrate intake. Table 3
shows an increase, significant or tendency, in total DM intake with TMR compared to
SEP. When analyzing the components of intake, although the tendency is that concentrate and
silage intakes increase with TMR, most studies found the increase in silage intake
significant, while no difference in concentrate. It can be stated that silage intake increase with
TMR and explains the higher total DM intake with this feeding method.
Reasons for total DM increase with TMR can be explained because the rejection of unpalatable
feeds is less possible (Phipps et al., 1984). Cooke et al. (2004) showed that feed refusals with
TMR contained all the feed components while SEP feeding refusal included mainly grass and
maize silage. Another possible reason is the extra processing of the feed when preparing the
TMR (as it makes it more compact with less fill), or the fact that when TMR is offered is once
and constantly available on the feed pen, as different from SEP feeding, when feeding is normally
done two times daily (Keane et al., 2006).
17
Table 3: Compilation of studies on the effect of TMR on total, silage and concentrate intake and
ADG on beef cattle.
Breed
G
C1
ratio
DM INTAKE (kg/day)
ADG (kg/day)
Total
Silage
Concentrate
Author
TMR
SEP
TMR
SEP
TMR
SEP
TMR
SEP
0.37
9.8
9.3
5.8
5.3
3.9
3.9
1.0
1.0
0.75
11.0
11.0
3.0
2.8
8.2
8.0
1.2
1.2
Keane et
al. (2006)
3 kg/d
6 kg/d
9.9
10.8
9.5
10.5
6.9
5.0
6.5
4.7
3.0
5.8
2.9
5.8
0.9
1.0
0.9
1.0
Caplis et
al. (2005)
0.33
7.8
6.9
5.2
4.6
2.59
2.31
1.2
1.0
0.66
7.9
7.3
2.7
2.4
5.3
4.91
1.1
1.1
H
0.77
9.8
9.5
1.3
1.1
Huuskonen
et al.
(2014)
Cooke et
al. (2004)
BF, CB
S
0.2
0.4
0.6
0.8
7.9
8.6
8.6
7.9
7.3
8.1
7.5
7.3
0.8
0.9
0.8
0.9
0.7
0.9
0.8
0.8
Petchey
and
Broadbent
(1980)
N/D
HS
9.9
9.3
0.9
0.9
Atwood et
al. (2001)
F, FxC
S
CxF, BxF, Ch
S
N
B
CB
*numbers in bold font have significant differences between TMR and SEP in that variable. 1 Concentrate ratio in the
of the diet used in each study
→ Effect on growth
When comparing different studies on animal performance, most do not show significant
improvements on daily live weights, slaughter weight, carcass weight or composition by TMR
compared to SEP (Keane et al., 2006, Caplis et al., 2005, Huuskonen et al., 2014, Atwood et al.,
2001, Petchey and Broadbent, 1980). For this, it would be logic to support Atwood et al. (2001)
and Huuskonen et al. (2014) who found a lower feed efficiency for TMR compared to SEP
feeding, as it increased DMI without having a clear effect on the gain.
On the other hand Bodas et al. (2014) and Casasús et al. (2012) found the same as Cooke et al.
(2004) mentioned before, with positive results when comparing maize silage-based diets as TMR
with all concentrate diets. In these studies, they did not find any differences in ADG, carcass
weight or dressing percentage between treatments, while Casasús et al. (2012) found better feed
efficiency for TMR as kg DM (Figure 5) as compared to an all concentrates diets. An example of
18
the weight evolution can be seen in Figure 4 as ADG in heifers showed no differences between
treatments. The reason for these positive results of TMR compared to CONC in this study as
compared to other studies, as suggested by Keane et al. (2006), may be due to the inclusion of
maize silage, a high energy content type of forage. The other studies only included grass silage or
if the maize silage was included it was accompanied by lower energy roughages as alfalfa hay
(Atwood et al., 2001). Moreover, Moujahed et al. (2009) showed no differences between TMR
and SEP in intake for dairy cows when the quality of the forage was oat hay as intake was
restricted by the low quality of the forage. Both studies suggest that the effect of the feeding
method on intake and performance depends on the quality of the forage part of the diet,
considering TMR suitable for high quality roughages.
LW (kg)
TMR
CONC
Age (months)
Figure 4: Effect of the feeding method on the monthly live weight of beef heifers. (Casasús et al.,
2012)
19
Intake (g DM/kg LW)
TMR
CONC
Age (months)
Figure 5: Effect of the feeding method on the monthly intake relative to the live weight (g DM/kg
LV).
→ Other factors are also involved on the effect of feeding method
As stated before the quality of the silage has an impact on the effect of TMR compared to SEP
and TMR will have better performance if the quality of the silage is higher. Another factor that
may affect the feeding method-effect is the ratio of the concentrate in the diet. Gordon et al.
(1995) reviewing dairy cow studies showed an interaction between the feeding method and
concentrate level although Keane et al. (2006), reviewing beef production of steers, only found an
interaction with concentrate level during the first 41 days of the experiment in daily gain. Also,
Caplis et al. (2005) studying this relation, just found an interaction on carcass gain results, having
an improvement of SEP feeding only when the concentrate was supplied in the higher proportion
(660 g/kg DM).
Gordon et al. (1995) in the same review suggested that the effect of the feeding method on animal
performance could be influence by another factor: i.e., frequency of feeding of the SEP feeding.
As an example, the studies described in Table 3 that found higher intakes for TMR, provided the
feed on the SEP treatment only twice a day. On the contrary, Yan et al. (1998) found no
differences in total DM intake comparing computerized out parlor feeding four times a day
separate with TMR in dairy cattle. Kaufmann (1976) explained that increasing the feeding
frequency would have a similar effect on buffering the ruminal pH than TMR. Increasing SEP
20
feeding frequency decreases the pH variations, as it changes the daily patterns of intake and
rumination, synchronizing the acid production and saliva production with each other (González et
al., 2012). As shown in Figure 6, the diurnal course of ruminal pH depends on the feeding
frequency. Feeding 14 times a day (continued line) will result in less variability of ruminal pH
during the day than feeding 2 times daily (dashed line).
Figure 6: Typical course of pH in the rumen in relation to the feeding frequency (Kaufmann,
1976).
Bodas et al. (2014) in the study mentioned above, which found no difference in animal
performance between a silage-based diet as TMR and all-concentrate diet, but it did find
differences in ruminal pH, being higher for the all concentrate diet. Although this is unexpected,
as concentrate diets tend to produce lower pH than silage diets, the explanation was based on the
feeding frequency. The TMR diet was supplied only early in the morning while on the other
treatment there was free access to concentrate, changing the intake pattern.
For this, it can be expected that the effect of the feeding method on intake and performance
depend on the diet and management characteristics, such as quality of the forage, ratio of
concentrate:forage in the diet and frequency of feeding rather than on the feeding method per se.
However, under most circumstances TMR will increase the DMI and silage intake and reduce
labor management, compared to the SEP. however, it requires investing on a mixer to produce
the TMR.
21
3. OBJECTIVES AND HYPOTHESIS
The main objective of this study is to evaluate different possibilities for beef bull production
systems to have a general overview of their viability for Danish beef production. For this, the
specific objectives involve:
Objective 1: To investigate if earlier weaning of the bulls can improve or match
conventional weaning, as it has already being demonstrated that increases the dam reproductive
performance.
The hypothesis is that:
→ Early weaning will increase ADG resulting in heavier calves by the time of normal weaning.
After normal weaning date, NW calves will increase their ADG, but it will not be enough to
compensate the previous lower ADG. For this, EW will have higher ADG in the total period,
and will be younger when slaughtered at the same fat-end point or same LW.
→ Despite EW being younger, the number of days spend on the feedlot will be higher, due to
earlier entry, leading into higher total intake.
→ Carcass conformation is expected not be affected significantly but, if finished at a target fat
end point EW will have lighter carcasses. However, if slaughter at the same LW, carcass
weight will not differ, although EW will have fatter carcasses.
Objective 2: Evaluate if silage-based diets can have as high growth rates as all-concentrate diets,
as they are cheaper and have a more suitable concentrate:roughage balance, lowering health
issues for the ruminant.
The hypothesis is that:
→ High quality silage-based diets after weaning will reach as high ADG as all-concentrate diets.
Feed intake as DM will be similar, but the intake of concentrate of silage-based diets is
expected to be reduced by increasing the intake of the silage.
→ Carcass conformation is expected to be better in all concentrate diets.
22
→ For silage-based diets, TMR will increase silage intake as compared to SEP feeding and as a
result total DM intake will increase although ADG would not differ between feeding
methods. For this, TMR will have worse feed efficiency.
→ Carcass traits will not be affected by the feeding method
Objective 3: Conclude if there is any suitable combination of weaning and post-weaning feeding
system in order to maximize performance and economically feasible at the same time. As there is
few information that can adjust to the Danish production system.
23
4. MATERIALS AND METHODS
4.1. STUDY SITE AND DATES
The study took place at the Danish Cattle Research Centre (Danmarks Kvægforskningscenter,
DKC) located in Foulum, Denmark. It was carried out in 2 consecutive years, 2007 (from July
2007 to June 2008) and 2008 (from June 2008 to May 2009).
4.2. ANIMALS AND MANAGEMENT
The original plan was to include 48 calves each year, having a total sum of 96 observations, with
eight blocks of six animals (each block representing a breed type) each year. However, due to
failure of animal delivery in the second year the delivery was of 45 animals, recording 93
observations (48+45). Additionally, some of these animals could not be used due to experimental
imbalance (i.e., one of a set of animals from the same herd died or were culled) while others were
not taken into consideration, as the particular block was only having 3 or 4 animals. Therefore,
despite of the use of a MIXED model procedures, it was decided to include some uneven and
incomplete blocks. This concludes in 83 observations in total: 43 in 2007 and 40 in 2008.
Animals were bull calves purchased from Danish beef cattle breeders. The breeds included in the
experiment were Simmental, Limousine, Charolais, Hereford, Angus and F1 crossbreds of these
breeds. The blocks of the study are described in Table 4.
Calves were purchased as sets. A set consisted of two calves that belonged to the same herd and
were born in similar dates, which were randomly weaned in the two different dates planned. The
ideal situation was to have in each block three sets (six animals), in which each animal was
submitted to the six treatments combinations (see below). If this ideal situation could not be
fulfilled, both calves of the set would be submitted to the same feeding strategy.
24
Table 4: Description of the blocks representing a breed in the two years of the study.
BLOCK
1
2
3
4
5
6
7
8
2007
2008
Charolais
Charolais
Hereford
Hereford
Hereford
Hereford
Limousine
Angus
Cross 50-75 Simmental
Limousine
Simmental
Limousine x Hereford
Limousine x Hereford
Simmental
Simmental x Limousine
Limousine
Animals were delivered to the experimental site after their particular weaning from the dams in
each farm at 3 or 6 months of age, referring to these as early and normal weaning respectively.
Animal management was performed based on DKC manual for calves and young stock. All cases
of illness and treatments were recorded for each animal individually.
4.3. HOUSING
After arrival (early weaned and normal weaned) calves were dehorned (if necessary) and
allocated into group pens in a closed barn with half wall curtains and natural ventilation. The pen
allocation was made in order to obtain the same average initial weight per group pen, having 6
pens in each year of the study. In addition, these six animals in one pen belonged to different
blocks. For this, each pen (6 in total representing the six treatments) contained animals belonging
to different breeds (one animal from each block) with a maximum of six animals per pen. The
pen floor was covered with deep litter and dispensed chopped straw barley with an automatized
dispenser, 4 times a day.
Each pen had 2 feeding stations (Insetec BV in Figure 7) and 2 cups of water with circulation
(frost-proof) and open water surface (Figure 8). The pens were 64.8 m2, calculating 10.8 m2 per
animal, when there were 6 animals per pen (Figure 9).
25
Figure 7: Feeding stations in each pen
Figure 8: Frost-proof water cups in the pens
Figure 9: Pens used in the study for the bulls
26
4.4. TREATMENTS AND DIETS
After weaning, calves were offered an acclimatization diet consisting of concentrate diet number
2 (Table 5) and straw for 14 days. After this period they were in the pens and allocated to one of
the 3 feeding treatments, each pen corresponding to one full treatment (weaning x feeding). This
procedure was carried out for both weaning groups, early and normal weaned calves.
There were two factors, weaning age and post weaning feeding. Weaning age had two levels:
Early Weaned calved at 3 months age and Normal Weaned calves at 6 months of age. Post
weaning feeding comprised three different diets to which the animals were assigned after each
weaning date (early and normal). The three diets were:
1-Concentrate (CONC): Ad libitum Concentrate. Diet number 1 was given up to 200 kg LW
(average of the observations) and concentrate diet number 2 from 200 kg LW to slaughter (see
Table 5 for diet composition). During the whole period, barley straw ad libitum was offered. The
change of diet in 2007 was on 10 September 2007 and for the 2008 cohort on 25 September 2008.
2- Total Mixed Ration (TMR): Consisting of concentrate:silage combination supplied as TMR.
The feeding period consisted of two different TMR diets. From start to 300 kg LW (average of
observations) TMR-1 was offered. It included 75% concentrate diet number 2 (Table 5) mixed
with 25% grass silage. After 300 kg LW to slaughter TMR-2 was supplied, consisting of 55% of
concentrate number 2 (Table 5) and 45% silage (all DM basis). TMR allowance was ad libitum.
Silage composition changed through the growing period (see Table 6 and Table 7). The change
from TMR-1 to TMR-2 was on the 31 October 2007 and 10 October 2008 for 2007 and 2008
trials respectively.
3- Separate Feeding (SEP): Using the same components at all times as used for the TMR but
concentrate and silage supplied in separate feeders. The concentrate a fixed allowance of 4 kg of
DM per day (with a maximum allowance of 2 kg per 12 hours) while grass silage was fed ad
libitum.
27
For this, the experiment had 6 treatments combining the two factors (2x3).
1- EW-CONC: Early weaned and CONC post weaning feeding system until slaughter.
2- EW-TMR: Early weaned and TMR post weaning feeding system until slaughter.
3- EW-SEP: Early weaned and SEP post weaning feeding system until slaughter.
4- NW-CONC: Normal weaned and CONC post weaning feeding system until slaughter.
5- NW-TMR: Normal weaned and TMR post weaning feeding system until slaughter.
6- NW-SEP: Normal weaned and SEP post weaning feeding system until slaughter.
4.4.1. Feed analysis and recording
Standard analysis was performed for the silage. The concentrate feed was purchased form a
commercial company. The analysis and composition of the concentrates and silages used in the
diets can be seen in Table 5 and Table 7, respectively.
Feed intake of concentrate and silage from Insetec feeders were automatically recorded and
transferred to the database (Figure 10). Straw intake was based on an estimated intake (and only
used for some calculations). For the CONC treatment the estimation was based on Jørgensen
(2008) study, where chopped barley straw intake was recorded to amount to 6 to 8% of the
Concentrate Intake expressed as kilograms of Dry Matter. This equals to 0.43 to 0.57 kg DM per
day for the CONC treatment. For SEP and TMR treatment it was estimated to be approximately
¼ of the straw intake of the CONC treatment, which equals 0.05 SFU/day of straw corresponding
to 0.22 kg DM based (1 SFU=4.38 kg DM of spring barley straw).
During 1 month after arrival, feed intake was assessed daily on the electronic database and
looking directly into the feeders and animal behavior to assure proper intake.
28
Table 5: Nutrient composition and ingredients of the concentrate diets.
Item
Analysis
Kg DM/SFU
Crude Protein (%)
Crude Fat (%)
Starch (%)
Cell wall (%)
Calcium g/kg
Potassium g/kg
Ingredients
Wheat
Barley
Corn
Peas
Sugar beet pulp pellet
Citrus pulp
Wheat bran / gluten feed
Green pills extra
Soybean meal / cake
Rapeseed meal / cake
Sunflower meal / cake
Corn gluten feed
Distillery products
Molasses
PFAD fatty
Rumen load index
Concentrate diets
1
2
1.00
1.02
17
13
4
4
305
330
180
200
10
8
4
4
%
%
20-30
20-35
8-10
10-15
10
10
5-10
2-5
10-20
10-20
2-10
5-10
0-5
0-5
3
3
8-15
0-5
2-10
2-10
0-5
0-5
0-5
0-5
0-5
0-5
2-4
2-4
1-2
1-2
91
97
Table 6: Silages used in TMR and SEP feeding per period.
2007 TRIAL
Start to 04 August 2007
5th August 2007 to Slaughter
2008 TRIAL
Start to 18 July 2008
19th July 2008 to 17th December 2008
18th December 2008 to 17 March 2009
18th March to Slaughter
Silage used
silage A
silage B
Grass C
Silage D
Silage E
Silage F
29
Table 7: Nutrient composition of the silages used in the study.
Grass silage
Item
kg/SFU
DM (%)
Kg DM/SFU
CP (%)
Fiber (%)
Sugars (%)
NDF (%)
Ca (g/kg DM)
P (g/kg DM)
Mg (g/kg DM)
pH
A
2.76
38.8
1.07
16.7
22.8
7.9
39.0
6.8
3.3
1.7
4.3
B
2.40
41.1
1.0
18.6
17.4
14.0
30.4
6.6
2.8
1.4
4.4
D
2.50
41
1.02
13.7
19.9
16.9
32.4
4.7
2.8
1.3
4.5
E
3.49
29.6
1.03
16.9
20.8
5.9
33.8
6
3.2
1.5
3.9
F
3.59
29.3
1.05
16.9
20.8
7.6
33.5
5.8
3.6
1.6
4.1
Fresh
grass
C
3.71
28.3
1.05
18
21.7
14.3
39
Figure 10: Automatic recorder used in the feeding stations.
4.5. SLAUGHTER
Slaughter criteria was based on an attempt to reach similar degree of fatness (at least 3 and not
above 4 on EUROP fatness score) of all breeds. This means that lean Limousine breed had to be
slaughter older and a fat Hereford younger. Therefore, the slaughter live weight was different
for the breed-group. This means that within breed a fixed body weigh at slaughter was
chosen in order to produce carcasses of similar fatness degree for the breed. The average
slaughter weight per breed used in this study can be seen in Table 8.
30
Table 8: Slaughter weight depending on Fat score criteria of each breed
Breed
Hereford
Angus
Limousine
Simmental
Charolais
Average
weight
507
516
544
579
581
Maximum
weight
534
533
575
622
623
Minimum
weight
484
490
528
538
548
Fat score
4
4
3
3
3
After reaching the slaughter criteria, animals were transported via commercial trucks to be
slaughtered at Danish Crown Beef located in Aalborg, Denmark. The set of calves from a given
block (of both weaning dates) was always slaughtered on the same day.
4.6. MEASUREMENTS
Weight: Calves were weighed at arrival and the day after in order to make the purchase
agreement with the farmer. After one week of arrival, calves were double weighed again. After
this, weighing was performed every 14 days until slaughter. Before departure to the
slaughterhouse, animals were double weighed again.
-Carcass: Carcass weight, conformation and fat score were recorded at the slaughterhouse.
Carcasses were graded following the European Grading System. Carcass conformation was based
on the EUROP classification with a 15 point scale where 1 (P-) is the poorest score and 15 (E+)
the highest. EUROP fat score was a 5 point scale (1=leanest, 5=fatter).
4.7. CALCULATIONS
-Growth rates: calculated in 4 different periods: from birth to 6 months of age, from 6 months age
to slaughter,
from weaning of the animals to slaughter (different weaning treatments has
different entry date as EW enters at 3 months of age and NW enters at 6 months age), and from
birth to slaughter. Calculations are based on the live weights of the animals.
31
-Feed intake: recording from fresh based concentrate and silage were calculated to kg DM and as
Feed Units. The Feed Unit system used is a net energy (NE) system Scandinavian Feed Units
(SFU), where 1 SFU equals to 7.89 MJ of NE (Weisbjerg and Hvelplund, 1993).
-Feed efficiency: Calculated as 3 different rates: Feed Conversion Rate expressed as kg of DM
per kg of weight gain and SFU per kg of gain. Also calculated as Gain to Feed ratio, as kg of
weight gain per kg of DM intake.-days on feed: calculated from 6 months to slaughter and from
the entry of the animals to slaughter
-digestible CP: expressed as both grams per kg DM intake or grams per SFU.
-Carcass dressing percentage: calculated as cold carcass weight divided by the live weight at
slaughter.
4.8. STATISTICAL ANALYSIS
4.8.1. Experimental design
Proc Mixed in SAS was used for analysis and degrees of freedom were estimated by KenwardRoger estimation. The experimental design is a two factorial incomplete block design with
weaning and feeding as fixed effects. The design of incomplete blocks was chosen, as some
blocks were incomplete (nine complete blocks, seven incomplete blocks). By using the mixed
model, it was less problematic to have a dataset with some complete blocks included. The
block includes the genotype effects (breed).
4.8.2. Model
Y = μ + YEAR + BLOCK (YEAR) +SUB-BLOCK (Block*Year) + Weaning + Feed + Weaning
×Feed + ε
32
Where μ is the mean, Year is 2007 (43 observations) and 2008 (40 observations). A total of 83
observations.
BLOCK is 1, 2, 3, 4, 5, 6, 7, 8 (but some blocks are incomplete) per year. Each block
represented a breed or crossbreeding and included Hereford (n=4), Angus (n=1), Simmental
(n=2), Charolais (n=2), Limousine (n=3) and crossbreds (n=4). BLOCK was assumed random
and normally distributed. SUB-BLOCK is the set of calves explained above.
WEANING is 3 (EW) or 6 months (NW), FEEDING is CONC, TMR or SEP, WEANING ×
FEEDING is the interaction and ε is the residual, which has mean 0 and assumed normally
distributed.
33
5. RESULTS
5.1. GROWTH RATES AND LIVE WEIGHTS.
Least squares means (LSM) and Standard errors (SEM) for growth rates, body weights, and age
at slaughter are shown in Table 9. As no interaction was detected for any of the variables, the
results are shown for weaning and feeding separately and not shown for the 6 treatments
combining the factors. This would make it easier for the analysis and understanding of effect of
each factor.
Table 9: : LSM and SEM for growth rates, weight and age at slaughter of the bulls in different
periods of the study.
Weaning (W)
Feeding (F)
P value
Variable
EW
NW
SEM
CONC
TMR
SEP
SEM
W
F
WxF2
Growth rate (kg/day)
Birth- Weaning*
1.023 1.151 41.30
1.084
1.089
1.089 56.41
0.002
0.99
0.41
Birth- 6 months
1.204 1.151 38.53
1.174
1.194
1.162 49.92
0.15
0.84
0.37
6 months-Slaughter
1.621 1.646 43.24
1.667
1.607
1.626 51.17
0.52
0.52
0.97
Weaning*-Slaughter
1.572 1.647 44.99
1.650
1.596
1.583 50.83
0.04
0.33
0.79
Birth-Slaughter
1.409 1.402 31.11
1.414
1.406
1.397 37.06
0.79
0.9
0.42
<0.001 0.91
0.64
Live Weight (kg)
Weaning weight
145
250
7.57
200
197
195
9.40
6 months age
267
250
8.60
261
260
256
11.43
0.04
0.93
0.68
Slaughter
559
560
7.18
559
558
562
7.34
0.82
0.43
0.41
375
7.95
0.78
0.58
0.57
Age at slaughter
days
369
371
6.14
365
370
*Weaning age differs between groups (EW= 3 months NW= 6 months)
Growth rates were analyzed in different periods of the study: from birth to weaning date, from
birth to 6 months age, from 6 months to slaughter, from weaning to slaughter and from birth to
slaughter. Higher growth rates were detected for NW in the periods from birth to weaning and
34
from the weaning to slaughter (P<0.05). The particularity of these two periods is that the weaning
date differs between weaning treatments as explained before (3 months age for EW and 6 months
age for NW). NW had 128 grams higher daily gains from birth to weaning than EW group (1.151
vs 1.023 kg/day). Growth between weaning and slaughter also differed between the weaning
treatments, the length of this period is also different among weaning groups. For this period, NW
had 75 grams higher gains (1.647 vs 1.572 kg/day). Growth between the two weaning dates was
not analyzed statistically, as there is no recording from 3 months to 6 months of age of the
NW bulls, as they were still in the farms with the dams. No effect of weaning was detected for
the other growth rate periods (P>0.05).
Body weight was statistically analyzed in three stages of the study: at weaning time, 6
months of age and slaughter. The difference of LW at weaning (P<0.001) is logical, as the
experimental design established that EW will enter at 3 months of age while NW will enter the
experiment with 6 months of age. For that reason, higher weight at weaning for NW is due to
difference in age due to the design of the study.
EW group were 17 kg heavier than NW at 6 months age (P<0.05). Although there was no
statistical difference in growth from birth to 6 months between weaning treatments (P>0.05),
results show a tendency that EW had 53 grams higher growth from birth to 6 months of age.
Body weight at slaughter showed no differences between weaning groups (P>0.05). Slaughter
weight (see criteria in section 4.6) was achieved at the same time, having no differences in age
when slaughtered (P>0.05) between weaning groups. Both weaning groups achieved their
slaughter weight at approximately 1 year of age.
Feeding had no effect on growth, body weight at any period analyzed nor on age at slaughter
(P>0.05). No interaction between Weaning and Feeding (WxF) was found in any of the variables
(P>0.05).
35
5.2. FEED INTAKE, FEED EFFICIENCY AND DAYS AT FEED.
The variables described in this section were analyzed in two different periods. The first period
analyzed from 6 months age to slaughter. The second period was defined from weaning age to
slaughter. As mentioned before, weaning date depends on the weaning strategy. Therefore, for
EW this period comprised from 3 months age to slaughter and for NW from 6 months age to
slaughter.
5.2.1. 6 months age to slaughter:
Table 10 shows LSM and SEM for concentrate, silage, total and digestible CP intake expressed
as kg of DM per day and SFU per day. It also shows results for Net Energy intake, Feed energy
concentration (NE/DM), Feed Conversion Efficiency (expressed as kg DM per kg gain and SFU
per kg gain) and gain to feed ratio expressed as kg gain per kg DM. Intake of straw was estimated
as explained in section 4.5. In this case, interactions were detected, so Table 10 shows the effect
on the 6 different treatments, rather than the factors separately, as shown in Table 9.
There was no effect of weaning on any of the factors evaluated from 6 months to slaughter
(P>0.05). Feeding strategy had an effect over all components of the intake (concentrate and
silage) and the total intake in both expression units (P<0.001). However, the tendency of the
effect of feeding on total intake changes depending on how the intake unit was expressed. Total
intake expressed as kg of DM per day was higher for the TMR treatment with no statistical
difference between SEP and CONC treatment (7.6 vs 7.2 vs 7.1 kg DM/day respectively).
However, when Total Intake was analyzed in SFU per day, TMR and CONC had the highest
values, with SEP having the lowest intake expressed as SFU/day (8.0 vs 7.8 vs 7.4 SFU/day
respectively). When intake was analyzed as NE (NEI), results also showed that CONC and TMR
had the highest intakes.
When analyzing the components of the intake (concentrate intake and silage intake) the highest
concentrate intake, expressed both ways, was for CONC treatment (P<0.001). There is no
36
recording of silage intake on this treatment due to the design of the study, which did not offer this
strategy any silage. It is important to emphasize the comparison between TMR and SEP as these
strategies only differ in the way the components were supplied to the animal (as mixed ration or
separately) and in the ratio between them (fixed and variable, respectively). TMR had higher
concentrate and lower silage intake compared to SEP treatment no matter the unit of expression
(kg DM/day or SFU/day) (P<0.001).
Feed efficiency was analyzed in three ways. Feed Conversion Efficiency (FCE) as kg DM per
kg gain, SFU per kg of gain and finally as Gain to feed (G:F) expressed as kg of gain per kg
of DM. TMR feeding strategy had the poorest efficiency regardless how the efficiency unit
(P<0.001)., while there is no statistical difference between SEP and CONC treatment (P>0.05).
Interactions between weaning and feeding existed for Feed Energy Concentration (NE/DM) and
digestible CP (g/SFU) (P<0.05). For Digestible CP as g/SFU the highest values were found for
the SEP treatment, but differences were higher between SEP and the other feeding strategies in
the NW bulls. For the existing interaction of NE/DM, the TMR resulted in second place after
CONC, but the concentration was higher when the animals were on NW treatments.
37
Table 10: LSM and SEM for daily intake of concentrate, silage, total, digestible crude protein and
feed efficiencies of the bulls in the period from 6 months of age to slaughter.
Weaning (W)
Feeding (F)
P value
Variable
EW
NW
SEM
CONC
TMR
SEP
SEM
W
F
WxF
3.4c
3.8a
0.22
7.2b
0.12
0.13
0.18
0.59
0.45
0.44
<0.001
<0.001
<0.001
0.08
0.25
0.42
58.1b
1.46
0.46
<0.001
0.35
3.7c
3.7a
0.05
7.4b
0.13
0.13
0.19
0.59
0.46
0.46
<0.001
<0.001
<0.001
0.08
0.25
17.49
747b
875a
847a
0.45
96c
110b
115a
Energy concentration
0.006
8.7a
8.2b
8.1c
19.65
0.78
0.74
0.36
<0.001
<0.001
0.4
0.002
0.009
0.20
<0.001
0.03
4.4b
4.6b
0.08
0.09
0.09
0.11
<0.001
<0.001
0.59
0.55
0.23a
0.004
0.11
<0.001
0.62
Intake (kg DM/day)
Concentrate
Grass Silage
Straw2
Total3
5.0
3.51
0.22
7.31
5.0
3.41
0.22
7.31
0.09
0.12
0.16
7.1a
0.57
7.1b
4.6b
3.1b
0.22
7.6a
Net energy intake
(MJ/day)
Concentrate
Grass Silage
Straw
Total
61.2
5.6
3.31
0.05
7.81
60.5
1.32
5.5
3.31
0.05
7.71
Intake (SFU/day)
0.10
7.8a
5.0b
0.12
2.9b
0.14
0.05
0.17
7.8a
8a
61.6a
62.9a
0.35
Digestible CP
g/day
g/SFU
825
107
821
107
MJ NE/ kg DM
8.3
8.4
FCE
kg DM/kg gain
SFU/kg gain
4.6
4.8
4.4
4.7
0.07
0.07
4.3b
4.7b
4.8a
5.0a
Gain to Feed
kg gain/kg DM
0.22
0.23
0.003
0.23a
0.21b
1
Includes only two of the three claims, ie 59 of the total of 83 calves. Therefore, the sum of concentrated feed, grass silage is not
equal to total.. 2Estimated. 3Straw not included.
5.2.2. From weaning to slaughter
Table 11 lists for this period the LSM and SEM for concentrate, silage and total feed intake
expressed as SFU/day, FCE (SFU/kg gain), digestible crude protein intake (expressed as g per kg
of DM and SFU) and days at feed as the number of days the animals spend on feed until
slaughter.
38
Table 11: LSM and SEM for daily intake of concentrate, silage, total, digestible crude protein,
feed efficiencies and days on feed of the bulls in the period from weaning age to slaughter.
Variable
EW
CONC TMR
SEP
NW
CONC
TMR
SEP
SEM
P-value
W
F
WxF
Intake (SFU/day)
Concentrate
Grass Silage1
Straw 2
Total1
6.78b
0.14
4.23d 3.48e
2.39c 2.65bc
0.05
0.05
7.74a
0.14
5.15c
2.74b
0.05
3.68e
3.57a
0.05
0.16
0.12
6.96a
6.67a
7.93a
7.96a
7.29b
4.9a
6.16b
<0.001
<0.001
0.003
<0.001
<0.001
0.002
-
-
-
0.19
<0.001
<0.001
0.51
4.44b
0.10
<0.001
0.006
0.35
856a
116a
21.70 <0.001 <0.001
0.87 <0.001 <0.001
0.002
195
11.09 <0.001
FCE
SFU/kg gain3
4.22ab
4.26a
4.01b
4.66ab
Digestible CP
g/day
g/SFU
695b
103d
739b
110c
699b
113b
733b
96e
874a
109c
<0.001
Days at feed
256
270
280
186
191
0.33
0.67
1
Includes only two of the three claims, ie. 59 of the total of 83 calves. Therefore, the sum of concentrated feed, grass silage is not
equal to total. 2 Estimation based on the explanation mentioned in Materials and Methods chapter. 3Includes straw
Both factors, Weaning and Feeding, had an effect on Total Feed Intake (P<0.001) although no
interaction was recorded (P>0.05). NW had 1.1 SFU/day higher feed intake than EW. When
analyzing feeding strategy effect, SEP treatment had the lowest Total Feed intake, while there is
no difference between the other two feeding strategies. It seems that the tendency is the same as
the period from the 6 months to slaughter period when expressed as SFU.
An interaction existed between Weaning and Feeding for concentrate and silage intake for this
period (P<0.05). Both interactions can be seen in Figure 11, where the intake of concentrates and
silage expressed as SFU per day are shown for the six different treatment combinations (Weaning
x Feeding).
39
Lowercase letters (a,b,c,d,e): significant difference (P<0.05)on concentrate intake between the treatments. Uppercase
letters (A,B,C): significant difference on silage intake between treatments.*Straw intake is not included
Figure 11: Concentrate and silage intake as feed units (SFU/day) of bulls from the period from
weaning to slaughter.*
When analyzing the interaction WxF on concentrate intake, it is clear from Figure 11 that CONC
revealed the highest intake, regardless weaning groups, compared to the other feeding strategies.
Within CONC strategy, the NW had 0.96 SFU higher concentrate daily intake than their EW
pairs. This leads to NW-CONC having the highest concentrate intake of the 6 treatments
followed by EW-CONC. TMR followed the same tendency, where the NW had 0.92 SFU higher
concentrate intake their EW pairs. Both, NW-TMR and EW-TMR, displayed lower concentrate
intakes than EW-CONC group. SEP treatment had the lowest concentrate intake, with no
difference between weaning groups.
Silage intake was analyzed only for TMR and SEP feeding strategies, as CONC had no intake
because of the experimental design provided no silage for this feeding strategy (see section 4.4).
The existing interaction shows that the highest silage intake was obtained by the NW-SEP
bulls. This group was followed by NW-TMR and EW-SEP showing no difference with each
other. The EW-TMR had the lowest silage intake.
Feed efficiency was influence by weaning (P<0.001) and feeding(P<0.05), but no interaction
between the factors was detected (P>0.05). EW had better FCE than the NW bulls for this period.
40
The feeding strategy effect was defined by the SEP treatment having the best FCE while TMR
had the worse.
Days on feed refers to the number of days the animals spend under the feeding system after
weaning. The effect of weaning showed that EW spent 77 more days on feed than the NW group
in the whole study period (P<0.05). This difference was due to the earlier entrance of the EW as
there was no statistical difference on days spend on feed between 6 months age and slaughter
(P>0.05). No effect of feeding was detected on this variable (P>0.05).
5.3. CARCASS QUALITY AND TRAITS
LSM and SEM for carcass weight, dressing percentage, EUROP conformation and fat score are
list in Table 12. Weaning had only effect on carcass conformation score (P<0.05), being 0.6
points higher for NW bulls. Feeding strategy had an effect on carcass fatness (P<0.05) resulting
in leaner carcasses for the CONC treatment while SEP and TMR showed no difference. No other
quality parameter was affected and no interaction was recorded (P>0.05).
Table 12: LSM and SEM for carcass characteristics.
Variable
Carcass weight, kg
Dressing (%)
EUROP form
EUROP fat
Lean/fat colour
Weaning
Feeding
EW
NW
Sem
311
57.9
9.6
3.28
3.05
314
58.2
10.2
3.16
2.97
5.92
0.67
0.44
0.14
0.03
CONC TMR
311
57.7
10
2.98b
2.95
131
58
9.6
3.35a
3
P value
SEP
Sem
W
F
WxF
315
58.5
10.1
3.32a
3.07
6.13
0.72
0.48
0.15
0.04
0.10
0.22
0.39
0.25
0.35
0.35
0.94
0.43
0.47
0.33
0.04
0.21 0.005
0.07 0.08
41
6. DISCUSSION
In this study, we investigated whether there was a positive impact of earlier weaning on the bull
performance. Additionally, if after weaning silage-based diets could have as high ADG as an
all-concentrate diet, which is the usual diet used in Danish bull production system. Therefore, in
this study was important to consider the consequences of the possible combinations of weaning
and post-weaning feeding in the performance of the bulls and carcass characteristics. Most of the
previous studies base their research in American or other European production types, where
steers are the base of the production, using local breeds or the diets differs from the intensive
Danish system. Therefore, there was a need to investigate these factors in the Danish bull
production system, which is small and intensive.
6.1. GROWTH RATE AND BODY WEIGHTS
The magnitudes of the growth rates obtained in our study are comparable to the growth rates
found by some of the studies shown in Table 1 (Blanco et al., 2008, Blanco et al., 2009, Story et
al., 2000, Schoonmaker et al., 2004, Schoonmaker et al., 2003, Meteer et al., 2013), and they are
higher than the overall mean calculated. The studies mentioned are the ones who recorded the
highest growth rates of Table 1, approximately 1.5 kg/day for these periods. Therefore, it can be
stated all treatments in our study registered high growth rates for the study period.
Weaning age had no effect on the growth rates from birth to six months of age, although at the
end of this period EW were 17 kg heavier. As a difference from Table 1, our study could not
record NW calves weight at 3 months of age because the calves were in the farms. This is a
limitation of our study, as no certain conclusion can be taken on the performance of the bulls
between the two weaning dates (from EW date to NW date), as other studies did. However,
assuming that until 3 months of age all the bulls had the same growing rates (no weaning or
feeding was imposed at that time), and weighed 145 kg (weight of the EW calves at 3 months
age); it can be suggested that EW had higher daily gains than NW between weaning dates (EWNW), 1.36 and 1.17 kg/day, respectively. The detailed explanation can be seen in Table 13. This
42
assumption is supported by the fact that the growth rate of EW was higher in the period from
birth to 6 months age than from birth to weaning; meaning that after weaning EW increased their
growth rate. As a result, EW calves were heavier at the time of normal weaning age, matching the
reviewed studies in Table 1.
Table 13: Growth rates calculation for the period between weaning dates (EW-NW)
Item
Weight at EW (kg)
Weight at NW (kg)
Growth rate from EW to
NW (kg/day)
EW
145
267
NW
145 (assumption)
250
1.36 = (267-145)/90days 1.17 = (250-145)/90days
It is also important to point out that until 6 months age NW calves were raised in the farms, with
different raising systems. This was different from EW calves, who were submitted to the study at
3 months of age. As a result, a higher variability in the weaning weight of NW calves was
registered (weight at 6 month) as compared to EW calves (Figure 12). This higher variability may
be due to differences in the raising systems between the farms, such as different milk production
by the dams, different feeding resources and milk nutrient availability, use of creep feeding
systems, as explained by Lusby et al. (1981), Abdelsamei et al. (2005), Olesen et al. (2004) and
Grimes and Turner (1991a). As an example, some of the NW calves were more than 370 kg at the
time of weaning, which is higher than the expected on usual raising conditions. It can be
suggested that if NW were in a controlled raised environment with their dams during weaning,
the differences in body weight with EW may have been larger that the recorded by our study (17
kg of difference).
43
Figure 12: Body weight at weaning for EW (3 months weight) and NW (6 months weight).
The period from weaning to slaughter also showed differences between weaning groups, which
was higher for NW bulls. This period can be compared with the periods from NW to slaughter for
NW bulls and EW to slaughter for EW bulls from Table 1, as each period considers their
respective weaning time for each weaning group. Although there was not straight comparison
between these periods in the studies, it seems that in most cases NW had higher growth rates
from their respective weaning time (from NW-slaughter) than EW (from EW-slaughter) as our
study (Kubisch and Makarechian, 1987, Blanco et al., 2009, Blanco et al., 2008, Schoonmaker et
al., 2004, Schoonmaker et al., 2001).
The period from 6 months of age to slaughter can be compared with the results of the period from
NW-slaughter of the studies from Table 1, as in these periods both weaning groups were already
separated from their dams. The lack of a difference in growth rate in this period due to weaning
age had also being observed by some studies (Fluharty et al., 2000, Myers et al., 1999c, BarkerNeef et al., 2001, Blanco et al., 2009, Kubisch and Makarechian, 1987, Schoonmaker et al.,
2004). Despite that in our study no differences were detected either, NW started this period 17 kg
lighter than EW and reached the same weight for slaughter at the same age. This may infer that
between 6 months of age and slaughter NW bulls had higher growth rates during some shorter
period of time, which was not reflected in the overall growth rate of the whole period. Figure 13
44
shows growing rates of our study from weaning age to slaughter divided into shorter sub-periods.
Although it was not analyzed statistically, Figure 13 confirms that differences in growth were
detected in the period between 6 months age until slaughter. EW had higher gains at the
beginning, probably due to adaptation of the NW calves to the feeding system, while EW had
been fed these diets since 3 months of age. After this adaptation period, NW bulls had higher
daily gains than EW, and may be attributed to lower maintenance requirements as NW were
lighter (Blanco et al., 2008). Finally, at the end of the fattening period both registered the same
growth rates. This tendency matches the results from Blanco et al. (2008) as shown in Figure 3,
although the differences in growth rates were higher in that study, finding significantly higher
growth rates post-weaning for the NW bulls.
*
*Calculations shown in Table 13
Figure 13: Growth rates of EW and NW bulls from weaning to slaughter divided in sub-periods.
The overall LW evolution for both weaning groups is shown in Figure 14. It shows a regression
including a cubic effect, as it showed the best fit. Any additional polynomial beyond the third
order did not show a significant improvement on the R2. The regression curves of both groups
agrees what it has being discussed before, EW being heavier at 6 months age (180 days age) due
to higher growth rates between weaning dates. After 6 months age, both weaning groups obtained
the same slaughter weight at the same time but with a different evolution of the live weight
(Figure 13).
45
It can be concluded that weaning had an impact on the growth evolution, although the results at
slaughter were the same. This evolution of LW is also similar to the one reported by Blanco et al
(2008) shown in Figure 2, although in our study the differences were not as accentuated, probably
due to high pre-weaning growth of the NW in our study, as compared to that study (1,51 vs 0.8
kg/day respectively).
46
Figure 14: Live weight evolution of EW and NW from 90 days old (EW weaning date) to slaughter.
47
Concerning the post-weaning feeding regime, previous studies have demonstrated that high gains
could be obtained with diets including high quality silage (Keane and Allen, 1998, Huuskonen et
al., 2009, Bodas et al., 2014, Casasús et al., 2012) agreeing with our study, as no differences in
growth were found between the feeding strategies. Replacing an all-concentrate diet with a
silage-based diet will allow having cheaper diets with less health risks, as previously mentioned.
However, this similarity in growth rates does not mean that the animal performance was similar
between feeding regimes in our study, as feed intake and feed efficiency were affected by the
post-weaning diet used. This will be explained in the next section.
6.2. FEED INTAKE AND EFFICIENCY
Feed intake and feed efficiency were analyzed in two periods because different conclusions can
be taken from each period. The period from 6 months age to slaughter allows the comparison of
the bulls from the different treatments in the same age period, in the fattening phase of the bulls.
On the other hand, the period from weaning to slaughter allows the comparison of the production
systems as a whole, since animals were weaned. Although it is important to compare the three
feeding regimes, the comparison between SEP and TMR is key, as they were both silage based
diets, both cheaper alternatives and achieving similar animal growth rates than the CONC.
For both of the periods mentioned above, SEP feeding system had higher feed efficiency (as DM
and SFU) due to lower total intake as compared to TMR. Higher intake for the TMR corresponds
with the studies on Table 3. However, the lower intake of the SEP was defined by higher silage
intake and lower concentrate intake disagreeing with the same studies, who stated that TMR
increases silage intake.
Our study confirmed Moujahed et al. (2009), Gordon et al. (1995) and González et al. (2012)
findings on that the effect of the feeding method (TMR or SEP) can be altered by other feeding
factors, such as increasing feeding frequency or including high quality silage. In our study,
although the feeding frequency was twice a day, it was given 2 kg of concentrate in 12 hour
48
shifts, avoiding the high consumption of concentrate at the beginning of the day, regulating the
energy balance and thus probably the pH as explained by Kaufmann (1976) (Figure 6). The high
quality of the silage used in our study can be seen in Table 7, as the kg of DM per SFU is almost
as low as the concentrate diet (Table 5).
Examples of the daily consumption of an EW-SEP and a NW-SEP during the feeding period are
shown in Figure 15 and Figure 16, respectively. No matter the weaning strategy, the daily
allowance of 4 kg of concentrate was always consumed by the bulls, and the rest of daily total
intake was covered by the silage intake. As the silage used in our study was very good quality it
allowed enough energy intake for reaching high growth rates. Additional evidence is evolution of
the silage consumption through the feeding period, as the silage intake increased as the days in
feed and LW increased (Figure 14). This may be due to an increase of total requirements for
maintenance and production, which were covered by the increase of the silage intake. In the case
of the TMR (Figure 17), the mixed intrinsic characteristic of this feeding method does not allow
selection, making the consumption of both, silage and concentrate, increased as the total
consumption increased through the experiment. This resulted in higher concentrate intake than
SEP.
Kg concentrate
Kg silage
Figure 15: Records of the feeding pattern of an EW-SEP bull.
49
Kg concentrate
Kg silage
Figure 16: Records of the feeding pattern of an NW-SEP bull.
TMR
Figure 17: Records of the feeding pattern of an NW-TMR bull.
The period from weaning to slaughter allows the comparison of the treatments in the overall of
the study. It showed that EW had lower daily intake resulting in better feed efficiency. The higher
efficiency may be explained by the fact that EW were feed younger, were intake is generally
lower and high growth potential (Robelin and Tulloh, 1992). This can be supported by the fact
that there were no differences on daily intake between EW and NW on the period from 6 months
age to slaughter but they from weaning to slaughter EW had lower daily intake, so the better
efficiency of EW can be allocated to the period between weaning times.
50
Despite this, higher total, silage and concentrate intake were registered for EW explained because
they spent more days under feeding, due to earlier start in the feedlot (Figure 18). Figure 18 also
shows the total intake of the six treatments during the whole study. The EW system involved
more feed consumption no matter the feeding system used, meaning more feed cost. However,
the effect in the lower concentrate intake of the SEP as compared to the TMR was higher in the
NW bulls (7% lower in concentrate consumption of EW versus 14.2% in NW), having a higher
final effect on the reduction of the total intake between these two feeding strategies on the NW
bulls.
By analyzing the feeding systems, it is clear that SEP was the cheapest alternative, as in this
treatment the bulls consumed less total feed and concentrate as compared to TMR, no matter the
weaning system. Comparing all the treatments, NW-SEP seems to be the cheapest alternative in
feedlot terms, having the lowest concentrate and total intake in the study. Nevertheless, the
milking and grazing costs of NW are not included and should be taken into consideration when
analyzing the systems economically.
Figure 18: Silage, concentrate, straw and total intake for the six treatments of the study in the
overall period.
51
6.3. CARCASS CHARACTERISTICS
The final product, the carcass, registered differences between weaning ages in conformation
score; lower for EW. This difference was less than half a point and does not seem to have
importance from the practical point of view. This is in accordance with the studies finding little
or no difference between weaning strategies in carcass characteristics (Fluharty et al., 2000,
Kubisch and Makarechian, 1987, Arthington et al., 2005, Thompson et al., 2009, Schoonmaker et
al., 2001, Myers et al., 1999c, Pritchard et al., 1988). Moreover, carcass were fatter with silagebased diets, although neither had more than 4 points on the EUROP fat scale, as expected from
the slaughter criteria. These little differences between weaning ages and feeding strategies
support that all the 6 treatments reached acceptable market standards, viable for production.
52
7. CONCLUSIONS AND PERSPECTIVES.
Our results partially agree with the hypothesis, as EW were heavier at the time of normal
weaning, but the overall growth was similar for both weaning strategies. Results from the
present study demonstrate that although the evolution of growth differs, early weaning is a
viable strategy, not affecting the fattening production of bulls. However, as EW involves
more total feed intake this strategy should be used in certain production systems. For
example, when there is a shortage or low quality pasture for the dam-calf pair, risking the
performance of both. Furthermore, when the reproductive parameters of the farms are low,
as this tool would allow increasing them without affecting the calf performance. This can
be useful for Danish farms, which based their raising in marginal lands.
However, in order to compare which tool is more suitable for any production type, an
economic analysis should be made including not only feeding cost of the calf after
weaning, but also grazing or feed costs of the dam-calf pair and milk production costs.
In our study, pre-weaning growth of the calves was high, so there is a need to evaluate the
viability of early weaning when pre-weaning growth is restricted.
This study confirmed the hypothesis that, regardless the weaning strategy, high performance can
be achieved with high quality silage-based diets, meaning lower costs of feed, as expected in the
hypothesis. Moreover, the feeding method of silage-based diets depends on the type of diet and
frequency of feeding rather than the method per se confirmed previous studies. However, the
reader should consider that the study included high quality silage, so the feeding method
should be re-considered if the quality of the silage or the feeding frequency are lower. In order
to choose the feeding method, other aspects should be taken into account, such as the
possibility of investment for a mixer or work force availability, as TMR would signify
lower labor but higher investment.
53
Finally, our study demonstrate, as expected, that all the strategies analyzed are
viable for bull production, as they do not had a negative effect on the final
product, the carcass.
8. SUMMARY
The effect of age at weaning and different post-weaning feeding regimes on bull performance and
carcass quality was researched over a 2-year experiment. Eighty-three spring bull calves were
early-weaned (EW, 3 month old) or normally weaned (NW, 6 months old). After each weaning
date, bulls were taken to DKC installations, into an indoor feedlot and submitted to three different
feeding regimes until slaughter. All-concentrate diet ad libitum (CONC), a silage-based diet as
TMR with 65% concentrate ad libitum (TMR) or a silage based diet with a 4 kg fixed amount of
concentrate per day and silage ad libitum fed separately (SEP). Slaughter was performed based
on the fat score minimum 3 but not 4, in the EUROP fat scale. By the time of normal weaning
EW bulls were 17 kg heavier than NW bulls (P<0.05). However, after weaning NW calves
increased their growth rates until slaughter. Both groups achieved the same slaughter criteria at
the same age (1 year old) with the same slaughter weight (559 and 560 for EW and NW
respectively). For this, EW spent more days at the feedlot (P<0.001), as they were earlier
introduced, consuming more feed than their counterpart. Silage based diets had similar growth
rate as all concentrate diets. However, the SEP treatment had better feed conversion rate
(P<0.001), due to lower daily intake, as kg of DM of SFU. In conclusion, EW can match NW
performance and could be a viable tool in some production cases, like shortage of pasture for the
raising period. Moreover, silage based diets performed as well as the intensive all-concentrate
diet, making the feed cheaper and more balanced form the nutritional point of view. In our study,
TMR did not have a positive impact as compared to SEP, probably due to high silage quality and
the feeding frequency used in our study.
54
9. ACKNOWLEDGEMENTS
I would like to give special thanks to:
Mogens, my thesis supervisor, for giving me the opportunity to be part of this project and giving
me full support.
DKC for opening the doors and helping me with all my questions.
Aarhus University and University of Debrecen for hosting me as an international student and
gave me all the necessary tools for success.
My family and friends in Uruguay, who cheered loudly for me since the start of this master,
although we are 11600 kilometers apart.
My Danish family for their unconditional support in every step I gave.
My friends at Nørresø Kolleigum, for making this last semester fun, entertaining and full of
adventures.
Rane, for his love and belief in me.
55
10. REFERENCES
ABDELSAMEI, A. H., FOX, D. G., TEDESCHI, L. O., THONNEY, M. L., KETCHEN, D. J. &
STOUFFER, J. R. 2005. The effect of milk intake on forage intake and growth of nursing calves.
J Anim Sci, 83, 940-7.
AGNEW & CARSON 2000. The effect of a silage additive and level of concentrate supplementation on
silage intake, animal performance and carcass characteristics of finishing beef cattle. Grass and
Forage Science, 55, 114-124.
ANDERSEN, H. R. & INGVARTSEN, K. L. 1984. The influence of energy level, weight at slaughter and
castration on growth and feed efficiency in cattle. Livestock Production Science, 11, 559-569.
ARTHINGTON, J. D., SPEARS, J. W. & MILLER, D. C. 2005. The effect of early weaning on feedlot
performance and measures of stress in beef calves. J Anim Sci, 83, 933-9.
ATWOOD, S. B., PROVENZA, F. D., WIEDMEIER, R. D. & BANNER, R. E. 2001. Influence of freechoice vs mixed-ration diets on food intake and performance of fattening calves. J Anim Sci, 79,
3034-40.
BARKER-NEEF, J. M., BUSKIRK, D. D., BLACKT, J. R., DOUMIT, M. E. & RUST, S. R. 2001.
Biological and economic performance of early-weaned Angus steers. J Anim Sci, 79, 2762-9.
BLANCO, M., RIPOLL, G., ALBERTÍ, P., SANZ, A., REVILLA, R., VILLALBA, D. & CASASÚS, I.
2008. Effect of early weaning on performance, carcass and meat quality of spring-born bull calves
raised in dry mountain areas. Livestock Science, 115, 226-234.
BLANCO, M., VILLALBA, D., RIPOLL, G., SAUERWEIN, H. & CASASÚS, I. 2009. Effects of early
weaning and breed on calf performance and carcass and meat quality in autumn-born bull calves.
Livestock Science, 120, 103-115.
BODAS, R., POSADO, R., BARTOLOMÉ, D. J., TABERNERO DE PAZ, M. J., HERRÁIZ, P.,
REBOLLO, E., GOMEZ, L. J. & GARCIA, J. J. 2014. Ruminal pH and temperature, papilla
characteristics, and animal performance of fattening calves fed concentrate or maize silage-based
diets. Chilean journal of agricultural research, 74, 280-285.
CAPLIS, J., KEANE, M. G., MOLONEY, A. P. & O'MARA, F. P. 2005. Effects of supplementary
concentrate level with grass silage, and separate or total mixed ration feeding, on performance and
carcass traits of finishing steers. Irish Journal of Agricultural and Food Research, 44, 17.
CASASÚS , I., RIPOLL , G. & ALBERTÍ, P. 2012. Inclusión de silo de maíz en las dietas de cebo de
terneras: Rendimientos técnico-económicos y calidad de la canal y de la carne. Información
Técnica Económica Agraria, 108, 16.
COOKE, D. W. I., MONAHAN, F. J., BROPHY, P. O. & BOLAND, M. P. 2004. Comparison of
Concentrates or Concentrates Plus Forages in a Total Mixed Ration or Discrete Ingredient Format:
56
Effects on Beef Production Parameters and on Beef Composition, Colour, Texture and Fatty Acid
Profile. Irish Journal of Agricultural and Food Research, 43, 201-216.
COUNCIL, D. A. F. 2013. World Class Cattle Production
In: JENSEN, S. M. (ed.) 1st edition ed. Denmark: Danish Agriculture & Food Council.
DENMARK, S. 2015. http://www.statbank.dk/statbank5a/default.asp?w=1440.
DEVRIES, T. J. & VON KEYSERLINGK, M. A. 2009. Short communication: Feeding method affects
the feeding behavior of growing dairy heifers. J Dairy Sci, 92, 1161-8.
DIJKSTRA, J. 1994. Feed Evaluation for Ruminants Production and absorption of volatile fatty acids in
the rumen. Livestock Production Science, 39, 61-69.
FLUHARTY, F. L., LOERCH, S. C., TURNER, T. B., MOELLER, S. J. & LOWE, G. D. 2000. Effects of
weaning age and diet on growth and carcass characteristics in steers. J Anim Sci, 78, 1759-67.
FRENCH, P., O'RIORDAN, E. G., MONAHAN, F. J., CAFFREY, P. J., VIDAL, M., MOONEY, M. T.,
TROY, D. J. & MOLONEY, A. P. 2000. Meat quality of steers finished on autumn grass, grass
silage or concentrate-based diets. Meat Science, 56, 173-180.
FRENCH, P., O´RIORDAN, E., O’KIELY, P., CAFFREY, P. J. & MOLONEY, A. P. 2001. Intake and
growth of steers offered different allowances of autumn grass and concentrates. Animal cience,
72, 10.
GONZÁLEZ, L. A., MANTECA, X., CALSAMIGLIA, S., SCHWARTZKOPF-GENSWEIN, K. S. &
FERRET, A. 2012. Ruminal acidosis in feedlot cattle: Interplay between feed ingredients, rumen
function and feeding behavior (a review). Animal Feed Science and Technology, 172, 66-79.
GORDON, F. J., PATTERSON, D. C., YAN, T., PORTER, M. G., MAYNE, C. S. & UNSWORTH, E. F.
1995. The influence of genetic index for milk production on the response to complete diet feeding
and the utilization of energy and nitrogen. Animal Science, 61, 199-210.
GREENWOOD, P. L. & CAFE, L. M. 2007. Prenatal and pre-weaning growth and nutrition of cattle:
long-term consequences for beef production. animal, 1, 1283-1296.
GRIMES, J. F. & TURNER, T. B. 1991a. Early Weaning of Fall-Born Beef Calves: I. Preweaning Calf
and Cow Performance. Journal of Production Agriculture, 4.
GRIMES, J. F. & TURNER, T. B. 1991b. Early Weaning of Fall-Born Beef Calves: II. Postweaning
Performance of Early- and Normal-Weaned Calves. Journal of Production Agriculture, 4.
HIRONAKA, R., FREEZE, B., KOZUB, G. C. & BEAUCHEMIN, K. A. 1994. Influence of barley
silage:concentrate ratio on rate and efficiency of liveweight gain, diet digestibility and carcass
characteristics of beef steers. Canadian Journal of Animal Science, 74, 495-501.
57
HUUSKONEN, A., LAMMINEN, P. & JOKI-TOKOLA, E. 2009. The effect of concentrate level and
concentrate composition on the performance of growing dairy heifers reared and finished for beef
production. Acta Agriculturae Scandinavica, Section A — Animal Science, 59, 220-229.
HUUSKONEN, A. K., PESONEN, M. & JOKI-TOKOLA, E. 2014. Effects of supplementary concentrate
level and separate or total mixed ration feeding on performance of growing dairy bulls. 2014, 23,
9.
JØRGENSEN, K. F. 2008. Nutritional means to reduce subacute ruminal acidosis and the development of
liver abscesses in intensively-fed young bulls, Foulum, Aarhus Universitet, Det
Jordbrugsvidenskabelige Fakultet.
KAUFMANN, W. 1976. Influence of the composition of the ration and the feeding frequency on phregulation in the rumen and on feed in-take in ruminants. Livestock Production Science, 3, 103114.
KEANE, M. G. & ALLEN, P. 1998. Effects of production system intensity on performance, carcass
composition and meat quality of beef cattle. Livestock Production Science, 56, 203-214.
KEANE, M. G., DRENNAN, M. J. & MOLONEY, A. P. 2006. Comparison of supplementary concentrate
levels with grass silage, separate or total mixed ration feeding, and duration of finishing in beef
steers. Livestock Science, 103, 169-180.
KJELDSEN, A. & FISKER, I. 2002. Leverbylder hos slagtekalve. Dansk Kvæg.
KUBISCH, H. M. & MAKARECHIAN, M. 1987. EFFECTS OF DATE OF WEANING ON
POSTWEANING PERFORMANCE OF BULL CALVES OF THREE BREED GROUPS.
Canadian Journal of Animal Science, 67, 941-949.
LUSBY, K. S., WETTEMANN, R. P. & TURMAN, E. J. 1981. Effects of Early Weaning Calves from
First-Calf Heifers on Calf and Heifer Performance1,2. Journal of Animal Science, 53.
METEER, W. T., RETALLICK, K. M., FAULKNER, D. B., ADCOCK, J. W. & SHIKE, D. W. 2013.
Effects of weaning age and source of energy on beef calf performance, carcass characteristics, and
economics. The Professional Animal Scientist, 29, 469-481.
MEYER, D. L., KERLEY, M. S., WALKER, E. L., KEISLER, D. H., PIERCE, V. L., SCHMIDT, T. B.,
STAHL, C. A., LINVILLE, M. L. & BERG, E. P. 2005. Growth rate, body composition, and meat
tenderness in early vs. traditionally weaned beef calves. J Anim Sci, 83, 2752-61.
MOLONEY, A. P., KEANE, M. G., DUNNE, P. G., MOONEY, M. T. & TROY, D. J. 2008. Effect of
concentrate feeding pattern in a grass silage/concentrate beef finishing system on performance,
selected carcass and meat quality characteristics. Meat Science, 79, 355-364.
MOUJAHED, N., DABBOUSSI, I., AMMAR, S. B. H. & DAREJ, S. 2009. Effects of Concentrate
Feeding Strategy on Milk Production and Composition in Dairy Cows. Research Journal of Dairy
Sciences, 3, 4.
58
MOULD, F. L., ØRSKOV, E. R. & MANN, S. O. 1983. Associative effects of mixed feeds. I. effects of
type and level of supplementation and the influence of the rumen fluid pH on cellulolysis in vivo
and dry matter digestion of various roughages. Animal Feed Science and Technology, 10, 15-30.
MURPHY, T. A., FLUHARTY, F. L. & LOERCH, S. C. 1994. The influence of intake level and corn
processing on digestibility and ruminal metabolism in steers fed all-concentrate diets. J Anim Sci,
72, 1608-15.
MYERS, S. E., FAULKNER, D. B., IRELAND, F. A., BERGER, L. L. & PARRETT, D. F. 1999a.
Production systems comparing early weaning to normal weaning with or without creep feeding for
beef steers. J Anim Sci, 77, 300-10.
MYERS, S. E., FAULKNER, D. B., IRELAND, F. A. & PARRETT, D. F. 1999b. Comparison of three
weaning ages on cow-calf performance and steer carcass traits. J Anim Sci, 77, 323-9.
MYERS, S. E., FAULKNER, D. B., NASH, T. G., BERGER, L. L., PARRETT, D. F. & MCKEITH, F.
K. 1999c. Performance and carcass traits of early-weaned steers receiving either a pasture
growing period or a finishing diet at weaning. J Anim Sci, 77, 311-22.
NIELSEN, B. K. & THAMSBORG, S. M. 2005. Welfare, health and product quality in organic beef
production: a Danish perspective. Livestock Production Science, 94, 41-50.
O'KIELY, P. 2011. Intake, growth and feed conversion efficiency of finishing beef cattle offered diets
based on triticale, maize or grass silages, or ad libitum concentrate. Irish Journal of Agricultural
& Food Research, 50, 189-207.
OLESEN, M., ANDERSEN, B., MADSEN, P., MADSEN, N. & ANDERSEN, H. 2004. Foderoptagelse
og produktion hos forskellige biologiske typer af kødkvæg. DJF rapport, Husdyrbrug.
PETCHEY, A. M. & BROADBENT, P. J. 1980. The performance of fattening cattle offered barley and
grass silage in various proportions either as discrete feeds or as a complete diet. Animal Science,
31, 251-257.
PETERSON, G. A., TURNER, T. B., IRVIN, K. M., DAVIS, M. E., NEWLAND, H. W. & HARVEY,
W. R. 1987. Cow and Calf Performance and Economic Considerations of Early Weaning of FallBorn Beef Calves1,2,3. Journal of Animal Science, 64.
PHIPPS, R. H., BINES, J. A., FULFORD, R. J. & WELLER, R. F. 1984. Complete diets for dairy cows: a
comparison between complete diets and separate ingredients. The Journal of Agricultural Science,
103, 171-180.
PRITCHARD, R. H., ROBBINS, M. A., GEE, D. H. & PRUITT, R. J. 1988. Effect of Early Weaning on
Feedlot Performance and Carcass Characteristics of High Growth Potential Feeder Calves. In:
UNIVERSITY, S. D. S. (ed.) South Dakota Beef Report.
ROBELIN, J. & TULLOH, N. M. 1992. Patterns of growth of cattle. In: R., J. & C., B. (eds.) Beef cattle
production. Amsterdam: Elsevier.
59
ROBISON, O. W., YUSUFF, M. K. M. & DILLARD, E. U. 1978. Milk Production in Hereford Cows I.
Means and Correlations1,2. Journal of Animal Science, 47, 131-136.
SCHOONMAKER, J. P., CECAVA, M. J., FLUHARTY, F. L., ZERBY, H. N. & LOERCH, S. C. 2004.
Effect of source and amount of energy and rate of growth in the growing phase on performance
and carcass characteristics of early- and normal-weaned steers. J Anim Sci, 82, 273-82.
SCHOONMAKER, J. P., CECAVA, V. M., FAULKNER, D. B., FLUHARTY, F. L., ZERBY, H. N. &
LOERCH, S. C. 2003. Effect of source of energy and rate of growth on performance, carcass
characteristics, ruminal fermentation, and serum glucose and insulin of early-weaned steers. J
Anim Sci, 81, 843-55.
SCHOONMAKER, J. P., FLUHARTY, F. L., LOERCH, S. C., TURNER, T. B., MOELLER, S. J. &
WULF, D. M. 2001. Effect of weaning status and implant regimen on growth, performance, and
carcass characteristics of steers. J Anim Sci, 79, 1074-84.
STEEN, R. W. J. 1995. The effect of plane of nutrition and slaughter weight on growth and food
efficiency in bulls, steers and heifers of three breed crosses. Livestock Production Science, 42, 111.
STORY, C. E., RASBY, R. J., CLARK, R. T. & MILTON, C. T. 2000. Age of calf at weaning of springcalving beef cows and the effect on cow and calf performance and production economics. J Anim
Sci, 78, 1403-13.
THOMPSON, M. M., SCHAUER, C. S., ANDERSON, V. L., ILSE, B. R. & MADDOCK, R. J. 2009.
Impact of Weaning Date on Calf Growth and Carcass Traits. In: CENTER, N. C. R. E. (ed.)
NDSU Beef Feedlot Research Report. North Dakota: NOrth Dakota State University.
VAN HOUTERT, M. F. J. 1993. The production and metabolism of volatile fatty acids by ruminants fed
roughages: A review. Animal Feed Science and Technology, 43, 189-225.
VESTERGAARD, M., JØRGENSEN, K., ANDERSEN, J., CAPION, N. & ANDERSEN, H. R. 2003.
Færre Leverbylder - faktorer af betydning. Bilagsmappe Dansk Kvæg Kongres.
WATERMAN, R. C., GEARY, T. W., PATERSON, J. A. & LIPSEY, R. J. 2012. Early weaning in
Northern Great Plains beef cattle production systems: II. Development of replacement heifers
weaned at 80 or 215 d of age. Livestock Science, 148, 36-45.
YAN, T., PATTERSON, D. C. & GORDON, F. J. 1998. The effect of two methods of feeding the
concentrate supplement to dairy cows of high genetic merit. Animal Science, 67, 395-403.
ZEA, J. & DÍAZ, M. D. 1990. Producción de carne con pastos y forrajes. Mundi Prensa.
ZEA SALGUEIRO, J., DÍAZ DÍAZ, M. D. & CARBALLO SANTAOLALLA, J. A. 2009. Efecto del
acabado sobre la calidad de la canal de terneros y terneras alimentados con ensilados. Archivos de
Zootecnia, 58, 11-22.
60