Group size and floor-space allowance can affect weanling-pig performance
B. F. Wolter, M. Ellis, S. E. Curtis, E. N. Parr and D. M. Webel
J Anim Sci 2000. 78:2062-2067.
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Group size and floor-space allowance can affect weanling-pig performance1
B. F. Wolter*, M. Ellis*,2, S. E. Curtis*, E. N. Parr†, and D. M. Webel†
*Department of Animal Sciences, University of Illinois, Urbana 61801 and
†United Feeds, Inc., Sheridan, IN 46069
ABSTRACT: Crossbred weanling piglets (n = 1,920;
mean initial BW, 5.3 ± .7 kg) were used in two 9-wk
trials employing a randomized block design in a 2 × 2
factorial arrangement of treatments to determine effects of group size (20 [Small = S] or 100 [Large = L] pigs/
pen) and floor-space allowance (calculated requirement
[CR] or calculated requirement less 50% of estimated
“free space” [CR-50]) on growth performance. Free
space was estimated for each group size. From wk 1
through 4 after weaning, S and L groups at CR were
allowed a floor space of .17 m2/pig, and at CR-50, S
and L groups were allowed .15 m2/pig and .13 m2/pig,
respectively. From wk 5 through 9 after weaning, all
CR treatment pigs were provided a floor space of .38
m2/pig, and for the CR-50 treatment, S and L pigs were
allowed .32 m2/pig and .28 m2/pig, respectively. Piglets
had free access to feed and water. Feeder-trough space
per pig was the same for both group sizes. Feed-intake
data were collected for only wk 1 through 4. Group
size by floor-space allowance interactions (P < .05) were
found for gain/feed ratio (G/F) for wk 1 and wk 2 through
4, but not for wk 1 through 4. Piglets in L groups were
lighter (P < .001) at the end of wk 1, 4, and 9 by 2, 4,
and 5%, respectively, and had lower ADG (6%; P <
.001) throughout the trial than S piglets. During wk 1
through 4, feed intake was lower (7%, P < .001) in L
piglets than in S piglets, but G/F was similar (P > .05).
Piglets in CR groups had greater ADG (5%; P < .01)
throughout the trial, with a greater G/F (P < .05) for
wk 1 through 4, and were heavier (P < .01) than those
in CR-50 groups at the end of wk 4 (3%) and 9 (4%).
Pigs in L groups had a greater within-pen coefficient
of variation in BW at the end of wk 9 than pigs in S
groups. Large groups and reduced floor-space allowance
reduced piglet growth performance in the nursery.
Key Words: Floor Space, Group Size, Pigs
2000 American Society of Animal Science. All rights reserved.
Introduction
Modern pig housing systems are expensive to construct and operate. Historically, the number of pigs per
pen (i.e., group size) and the floor area allowed per
pig (i.e., stocking density) have been key factors in the
design and use of pig houses. In recent decades, pigs
typically have been penned from weaning to market
weight in groups of 10 to 30 animals. Now, however,
group sizes of 50 to 100 or even more are being advocated by some as a management strategy to minimize
housing cost, maximize housing use, and improve overall profitability.
1
The authors gratefully acknowledge the Illinois Council on Food
and Agricultural Research for financial support of this research;
United Feeds, Inc., for cooperation and use of research facilities; and
Gro Master, Inc., for the loan of feeding equipment.
2
Correspondence. 216 Animal Sciences Laboratory (phone: (217)
333-6455; fax (217) 333-7088; E-mail: [email protected]).
Received August 26, 1999.
March 10, 2000.
J. Anim. Sci. 2000. 78:2062–2067
Research has demonstrated that pig performance
during the nursery and grow-finish production stages
varies with number of animals per group and the floorspace allowance (NCR-89, 1984; Meunier-Salaun et al.,
1987; Spicer and Aherne, 1987). Housing pigs at reduced floor space has been shown to have a negative
influence on feed intake and growth rate (Kornegay and
Notter, 1984; NCR-89, 1993). Furthermore, increasing
group size alters patterns of feed intake in pigs when
the amount of feeding space remains unchanged (Hyun,
1997), although the pigs in that study were kept in
relatively small groups of 2 to 12 pigs.
McGlone and Newby (1994) observed no differences
in growth rate in grow-finish pigs in groups of 40, 20,
or 10 when kept at constant floor-space allowance (.74
m2/pig). They analyzed pig postures over a 24-h period
via time-lapse video records to determine “free space”
(i.e., total floor space not occupied by any pig at any
particular moment). Free space increased with increasing group size under constant floor-space allowance.
In a second experiment, none, half, or all free space,
respectively, was removed from pens holding groups of
20 pigs. Removing all free space had a detrimental effect
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Nursery group size and floor-space allowance
Table 1. Floor-space allowances and pen dimensions for pigs housed in large or small
groups and provided the calculated requirement or calculated requirement
less 50% calculated “free space”
Floor-space allowances and pen dimensions
Group size/
Study week
Large
1−4
5−9
Small
1−4
5−9
Calculated requirement
(CR)
Calculated requirement less
50% calculated free space
(CR-50)a
Weight
range,
kg
m2/pigb
Length ×
width, m
m2/pigb
Length ×
width, m
5−15
15−40
.17
.38
4.6 × 3.8
8.5 × 4.6
.13
.28
4.6 × 2.9
6.3 × 4.6
5−15
15−40
.17
.38
1.9 × 1.8
4.2 × 1.8
.15
.32
1.8 × 1.7
3.6 × 1.8
a
“Free space” was calculated using the formula of McGlone and Newby (1994) for pigs of 93 kg BW at
.74 m2 of floor space as Y = .179 + .002092X, where Y is free space in m2 and X is number of pigs per group.
Based on this equation, the floor-space allowances minus 50% of free space for groups of 20 and 100 pigs
were equivalent to 85 and 74%, respectively, of the estimated requirement (.74 m2/pig) for pigs of this weight
(93 kg). These percentages were applied to the required floor-space allowances for the weights of the nursery
pigs used in the current study to calculate the floor spaces for the CR-50 treatments.
b
Space occupied by the feeder was subtracted from total pen space in the determination of space treatments.
on pig performance, but removing half did not. Therefore, when large group sizes are employed in commercial operations, perhaps total space per pig can be decreased without reducing growth rate. However, for relatively large group sizes (i.e., 100 pigs) there is a paucity
of data related to effects of and interactions between
group size and floor-space allowance on pig performance.
The objectives of the research reported here were to
quantify effects of and interactions between group size
(20 vs 100 pigs) and space allowance on weanling piglet performance.
Materials and Methods
Experimental Design. An experiment was conducted
to assess effects of two group sizes (20 [Small] or 100
[Large] pigs per pen) and two floor-space allowances
(calculated requirement [CR] and calculated requirement less 50% of calculated “free space” [CR-50]) on
performance of weanling pigs. The experiment was carried out in two trials with each trial using a randomized
block design with a 2 × 2 factorial arrangement of treatments with replicates (4/trial) blocked by day of weaning. The research was carried out at the Burton Russell
Swine Research Farm, United Feeds, Inc., Frankfort,
IN. The experimental protocol was approved by the
University of Illinois Laboratory Animal Care Advisory Committee.
Pen sizes were adjusted at the starts of wk 1 and wk
5. Thus, floor-space allowances were kept constant for
the first 4 wk after weaning and for the period from wk
5 through 9 (Table 1) and were determined based on
BW using the formula: floor-space allowance (m2) = k
× BW.667, where BW is in kilograms and k is a constant
(Petherick and Baxter, 1981). The value assumed for
k was .03 (Edwards and Armsby, 1988; Gonyou and
Stricklin, 1998). The BW assumed in these calculations
were 14 kg and 45 kg, which were the predicted end
weights at wk 4 and wk 9, respectively. Free space was
determined using the formula Y = .179 + .002092X,
where Y is free space/pig in square meters and X is
number of pigs per group, which is the relationship
developed by McGlone and Newby (1994) for pigs of 93
kg BW at .74 m2 of floor space. Based on this equation,
the floor-space allowances minus 50% of free space for
groups of 20 and 100 pigs were equivalent to 85 and
74%, respectively, of the estimated requirement (.74
m2/pig) for pigs of this weight (93 kg). These percentages
were applied to the required floor space allowances for
the weights of the nursery pigs used in the current
study to calculate the floor spaces for the CR-50
treatments.
Animals. A total of 1,920 piglets were weaned at 15
d of age (x = 5.3 ± .7 kg BW) and allotted to treatment
at either 22 h after weaning in Trial 1 or 2 h after
weaning in Trial 2. Piglets were held in groups of approximately 150 animals and allowed ad libitum access
to feed and water during the period before allotment.
Piglet genetic types were PIC Line 327 × Bunge Line
13 and Bunge Line 5 × Bunge Line 13 for Trials 1
and 2, respectively. Piglets were randomly allotted to
treatment pens from outcome groups of 12 piglets
formed on the basis of common gender and weight.
Diets and Housing. Piglets were given ad libitum access to a six-phase dietary regimen formulated to meet
or exceed NRC (1998) nutrient requirements. Diets
were fed according to a budget that allowed every pen
of pigs to consume the same quantity per pig of each
dietary phase. The dietary phases and calculated dietary analyses are given in Table 2.
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Wolter et al.
Piglets were housed in an insulated, mechanically
ventilated, curtain-sided, nursery house with fully slotted-metal (tribar, cross-sectional profile) flooring. The
house was divided into four equal rooms, and each room
accommodated one replicate of the trial. Pens were randomly allocated to treatment within a room. Pens were
equipped with one nipple drinker/10 pigs and a fourspace nursery feeder/20 pigs, giving 4 cm of feedertrough space/pig. Feeders were positioned in the center
of the pen for all pen designs, and were accessible from
both sides. Water nipples were placed at equal (25.4
cm) intervals on one wall in each pen. Pen divisions
and gates consisted of horizontal steel rods. The pen
dimensions and features are illustrated in Figure 1.
Air temperature was maintained using a thermostatically controlled heater and fan ventilation. The temperature setting was 25°C throughout wk 1 and was
reduced gradually during wk 2 through wk 4 to 22°C,
where it remained for the rest of the study period. During wk 1 after weaning, one heat lamp was provided
for every 20 pigs in Trial 1 or one propane brooder per
pen in Trial 2. Room temperature and relative humidity
were monitored using HOBO H8 Loggers (Onset Computer Corp., Bourne, MA), which measured and recorded data every 15 min. Data loggers were placed
42 cm above the floor in the middle of each room. Air
velocities were measured in each pen twice during wk
1 to determine the level of drafts. During wk 1 through
wk 4, an infrared thermometer was used to measure
interior surface temperatures at seven locations in each
pen (namely, four walls, ceiling, floor, and floor area
exposed to supplemental heat). Aerial ammonia and
hydrogen sulfide concentrations were monitored weekly
using dosimeter gas detectors (Animal Environment
Specialists, Marysville, OH) located 42 cm above the
floor.
Statistical Analysis. Pig performance data were analyzed as a randomized block design using the GLM
procedure of SAS (1990). Pen was considered the experimental unit. The model included effects of group size,
space allowance, the interaction of group size and space
allowance, trial, and replicate nested within trial.
Means were evaluated using PDIFF and STDERR options of SAS (1990).
Results and Discussion
Air temperature and relative humidity averaged 24.4
± 1.1°C and 39.7 ± 4.8%; 23.0 ± 1.2°C and 47.4 ± 7.5%;
and 22.3 ± 1.2°C and 48.9 ± 9.8% for wk 1; wk 2 through
4; and wk 5 through 9 of the study, respectively. Average interior surface temperature was 27.4 ± 1.6°C and
25 ± 2.1°C for wk 1 and wk 2 through 4, respectively.
No air velocity greater than 3.3 m/min was detected
within the pen area, indicating that few drafts were
present. Ammonia concentrations were low, averaging
8.3 parts per million over the 9-wk study period. No
hydrogen sulfide was detected.
Piglet BW and within-pen variation in BW (indicated
by the coefficient of variation for each weigh period) are
given in Table 3. There was an effect of trial on piglet
start weight and ADG during wk 1. However, there
were no interactions (P > .05) between trial and either
of the treatments. Pigs in Trial 1 were lighter (5.0 vs
5.6 kg BW; P < .01) and had a greater ADG during wk
1 (248 vs 157 g; P < .01) than those in Trial 2; however,
ADFI during wk 1 was similar (P > .05) for the pigs in
both trials and, consequently, gain/feed ratio (G/F) was
greater (P < .01) for those in Trial 1. The difference
between the two trials in growth performance could
have resulted from the longer time period between
weaning and start of test for Trial 1 compared with
Trial 2 (20 h vs 2 h, respectively).
Results relating to feed intake and gain:feed ratio for
wk 1 through 4 and growth rate for wk 1 through 9 are
given in Table 4. There were no interactions (P > .05)
between group size and floor-space allowance for any
of the variables evaluated for wk 1 through 4, or wk 1
through 9. However, there was an interaction (P < .05)
between group size and floor-space allowance for G/F
during wk 1 and wk 2 through 4 after weaning (Table
4). During wk 1, Large piglets at CR-50 had lower G/
Table 2. Dietary phases, approximate duration of phases, diet form,
and calculated nutrient analyses
Dietary Phase
Item
Approximate BW
weight range, kga
Diet form
I
II
III
IV
V
VI
—b
Pellet
4.5−5.9
Pellet
5.9−9.5
Meal
9.5−14.0
Meal
14.0−22.7
Meal
22.7−36.3
Meal
20.89
1.30
.83
.73
3235
21.14
1.30
.76
.66
3230
20.45
1.25
.76
.65
3215
Calculated analysis
CP, %
Lysine, %
Ca, %
P, %
ME, kcal/kg
26.75
1.85
.93
.85
3425
24.66
1.82
.96
.83
3381
22.17
1.48
.78
.76
3243
a
Diets were fed according to a budget allowing each pen of pigs to consume an equal quantity per pig of
each dietary phase.
b
First 48 h after weaning.
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Nursery group size and floor-space allowance
Figure 1. Plan view of pen designs for both group sizes
of weanling pigs. A, large group design, dimensions (m,
length × width) were 4.6 × 3.8 and 4.6 × 2.9, and 8.5 × 4.6
and 6.3 × 4.6 for CR (calculated requirement) and CR-50
(CR − 50% calculated free space), and wk 1 to 4 and wk
5 to 9, respectively. The dimensions of the feeder were
2.05 × .406 m and it provided ten 20.3-cm-wide eating
places on each side. B, small group design, dimensions
(m, length × width) were 1.9 × 1.8 and 1.8 × 1.7, and 4.2
× 1.8 and 3.6 × 1.8 for CR and CR-50, and wk 1 to 4 and
wk 5 to 9, respectively. The dimensions of the feeder were
.406 × .406 m and it provided two 20.3-cm-wide eating
places on each side.
F than those at CR, but the opposite was observed for
Small piglets: Small piglets at CR-50 had a greater G/
F than at CR. During the subsequent 3-wk period, the
interaction observed for G/F was the result of Small
piglets at CR-50 having a lower G/F than those at CR,
whereas Large piglets at CR and CR-50 had similar G/
F (Table 4). However, these differences were relatively
small, and there was no significant interaction for the
overall 4-wk period.
Effect of Group Size. The Large piglets were lighter
(P < .001) than the Small piglets at the end of wk 1, 4,
and 9 after weaning (Table 3). Variation in BW within
a pen was greater (P < .05) for Large piglets at the end
of wk 9 (Table 3). The Large piglets had lower (P < .001)
ADG and ADFI during wk 1, 2 through 4, and wk 1
2065
through 4 (Table 4). During wk 4 through 9, Large had
lower (P < .001, Table 4) ADG than Small piglets.
Previous studies have generally employed fewer pigs
per pen than the current study to evaluate any effect
of group size on pig performance during the nursery
period, and results have been inconsistent. Kornegay
and Notter (1984) found that, for weanling pigs (BW <
30 kg) at a constant floor-space allowance, ADG and
ADFI decreased as number of pigs per group increased
(3 through 32 pigs). However, McConnell et al. (1987)
observed no differences in ADG, ADFI, or G/F among
weaned piglets (6.4 kg) penned in groups of 8, 16, or
24 animals. Verdoes et al. (1998) reported higher ADG
and ADFI, but similar G/F for nursery piglets in groups
of 10 compared with 90, results that are similar to those
found in the present study. Any effect of group size on
voluntary feed intake may be due to greater “social
tension” in larger groups (Curtis, 1996).
In growing pigs (20 to 60 kg), Petherick et al. (1989)
observed a lower ADG for pigs in large groups (36 pigs/
pen) than for smaller groups (8 or 16 pigs/pen). Similarly, Gelhbach et al. (1966) reported decreased performance with increased number of pigs per pen (8 vs
16 pigs) in the grower period. Randolph et al. (1981),
however, found no performance differences between
group sizes of 5 and 20 during the grow-finish period
(20 to 90 kg). Hyun (1997) observed a lower ADG for
pigs in groups of 12 than for 2, 4, or 8 pigs per group
during the growing period; however, similar ADG was
observed for pigs penned in these group sizes during
the finishing period.
McGlone and Newby (1994) found similar grow-finish
performance by pigs in groups of 10, 20, and 40; however, pig injury and morbidity were greater for the pigs
in groups of 40. In the current study, morbidity (pigs
removed due to poor health) was less than 1% in all
treatment subgroups; however, caretakers reported
having increased difficulty identifying and treating sick
pigs in Large pens than for Small pens. Verdoes et
al. (1998) also commented that checking and treating
nursery pigs in groups of 90 was more complex than
those in groups of 10.
Effect of Floor-Space Allowance. Piglets on the CR-50
treatment had BW similar to CR piglets at the end of
wk 1 after weaning (Table 3). However, CR-50 piglets
were .41 and 1.64 kg lighter (P < .01) than CR piglets
at the ends of wk 4 and 9, respectively. Floor-space
allowance did not affect variation in piglet BW within
a pen at any point during the study (P > .05, Table 3).
This is in agreement with Kornegay et al. (1985), who
found no effect of floor-space allowance on variation in
piglet BW. In addition, floor-space allowance did not
affect ADG during wk 1 (Table 4). However, CR-50
piglets had lower (P < .01, Table 4) ADG for wk 2
through 4, wk 4 through 9, and wk 1 through 9.
Kornegay and Notter (1984) observed that both ADG
and ADFI increased with increasing floor-space allowance, and a similar but smaller effect was found for
feed-conversion efficiency. In the current experiment,
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Wolter et al.
Table 3. Effects of group size and floor-space allowance on piglet BW
and variation in piglet BW from 5 to 40 kg BW
Group sizea
Item
Large
Small
No. pigs
No. pens
1,600
16
320
16
Level of
significancec
Floor-space
allowanceb
CR
960
16
CR-50
Mean
SEM
Group
size
Floor
space
Group size ×
floor space
.01
.03
.12
.26
NS
***
***
***
NS
NS
**
**
NS
NS
NS
NS
.06
.37
.42
.41
NS
NS
NS
*
NS
NS
NS
NS
NS
NS
NS
NS
960
16
Weight, kg
Start of wk 1
End of wk 1
End of wk 4
End of wk 9
5.3
6.7
14.8
38.9
5.3
6.8
15.4
41.1
5.3
6.7
15.3
40.8
5.3
6.7
14.9
39.2
CV, %d
start of wk 1
End of wk 1
End of wk 4
End of wk 9
13.6
14.3
15.0
12.3
13.5
13.8
14.5
11.1
13.5
14.3
14.6
11.5
13.6
13.8
15.0
11.9
Group Size = Large (100 pigs/pen) and Small (20 pigs/pen).
Floor Space Allowance = CR (calculated requirement) and CR-50 (calculated requirement less 50% calculated “free space”).
c
NS, *, **, *** = not significant, P < .05, P < .01, P < .001.
d
CV = coefficient of variation values were determined from pig weights within pen.
a
b
Table 4. Effects of group size and floor-space allowance on piglet
growth performance from 5 to 40 kg BW
Group sizea
Item
Large
Pigs, No.
Pens, No.
Level of
significancec
Floor-space
allowanceb
Small
CR
1,600
16
320
16
960
16
4
4
9
9
193
385
337
624
503
212
411
361
662
535
204
407
356
659
531
Wk 1
Wk 2 to 4
Wk 1 to 4
200
553
465
221
590
498
213
574
484
CR-50
Group
size
Floor
space
Group size ×
floor space
3.0
4.6
3.7
6.2
3.8
***
***
***
***
***
NS
**
**
***
***
NS
NS
NS
NS
NS
3.9
9.6
7.4
***
**
***
NS
NS
NS
NS
NS
NS
Mean
SEM
960
16
Daily weight gain, g
Wk
Wk
Wk
Wk
Wk
1
2
1
5
1
to
to
to
to
201
389
342
627
507
Daily feed intake, g
209
568
478
Gain:feed
Wk 1
CR
CR-50
Wk 2 to 4
CR
CR-50
Wk 1 to 4
.98d
.94e
.93e
.97d
.70d,e
.70d,e
.73
.72e
.68d
.73
.74
.72
.015
*
.008
*
.004
NS
*
NS
Group Size = Large (100 pigs/pen) and Small (20 pigs/pen).
Floor Space Allowance = CR (calculated requirement) and CR-50 (calculated requirement less 50% calculated “free space”).
c
NS, *, **, *** = not significant, P < .05, P < .01, P < .001.
d,e
Means with differing superscripts for a variable with interaction between group size and floor-space
allowance differ (P < .05).
a
b
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Nursery group size and floor-space allowance
floor-space allowance did not affect (P >.05, Table 4)
ADFI during wk 1 through 4; however, G/F was greater
in CR piglets than in CR-50 piglets during the same
period.
Lack of interaction between group size and floorspace allowance indicated that Large piglets had ADG
similar to Small piglets at the reduced floor space allowance. However, actual floor-space allowance was lower
(13%) for Large compared with Small pigs on the CR-50
treatment. Therefore, the results of the current study
support the hypothesis of McGlone and Newby (1994)
that, as group size increases, it may be possible to reduce the total floor space per pig without hindering
performance. Our results suggest a reduction of less
than 50% of free space will be required to maintain feed
intake and growth rate in nursery pigs. However, the
relationship between group size and floor space was
not directly tested, and further research is required in
this area.
Decreasing floor-space allowance per pig may lead
to increased social tension and a greater incidence of
aggressiveness in pigs (Ewbank and Bryant, 1972; Randolph et al.,1981; Curtis, 1996). In the current experiment, however, casual observations revealed no sign of
abnormal behavior, such as tail or ear biting, as a result
of either increasing group size or reducing floor-space
allowance.
Implications
The results of this study highlight that the negative
effects on growth performance associated with the large
groups and the reduced floor-space allowance shown in
this study should be taken into account in the design
of nursery accommodation. However, these results also
suggest that floor-space allowances for maximum
growth performance may decrease with increasing
group size. Further research is warranted to investigate
this concept and to evaluate environmental designs
that may enhance feed intake and weight gain of piglets
kept in large groups and at reduced floor-space allowance.
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