©2012 Poultry Science Association, Inc.
Sperm production and testicular development
of broiler breeder males reared
on shortened growth cycles
J. R. Moyle,*1 D. E. Yoho,* S. M. Whipple,* A. M. Donoghue,† and R. K. Bramwell*
*Department of Poultry Science, and †Poultry Production and Product Safety Research
Unit, Agricultural Research Service, USDA, Poultry Science Center,
University of Arkansas, Fayetteville 72701
Primary Audience: Broiler Breeder Managers, Flock Supervisors, Researchers
SUMMARY
Feed restriction is an important tool used in the rearing of broiler breeders to control growth
and maintain BW. Feed restriction during the growing phase typically provides 60 to 80% less
feed than the birds would consume if provided feed ad libitum, resulting in a perceived animal
welfare issue. Because males are typically more rigorously feed restricted than females, this is
thought to be especially stressful to the growing cockerels. During this time, the reproductive
systems of the males are undergoing formative stages, and improper management can have
lifelong effects on their reproductive performance. Therefore, the objective of this study was
to rear males under feed management programs that would require less severe feed restriction
while still rearing replacement breeder males to the recommended target BW of 3.060 kg at 24,
21, 18, 15, and 12 wk of age, respectively. Males were placed at 3-wk intervals so that all males
were light stimulated on the same calendar date and at the same time and BW but at different
ages. A total of 5 treatment groups were used, based on age of the male at light stimulation. All
males were reared in the same light-controlled house at the University of Arkansas Research
Farm. Males were light stimulated and testicular development, semen analysis, fertility, and
mating activity were recorded for each group of males. To measure semen production, males
were housed in individual cages, with 24 males from each treatment group tested. Males light
stimulated at 18 wk of age had the highest semen volume (0.46 mL), followed by males light
stimulated at 24 (0.31 mL), 15 (0.29 mL), 21 (0.27 mL) and 12 wk of age (0.27 mL), respectively. Sperm count per ejaculate was highest for the males light stimulated at 18 wk of age,
followed by males light stimulated at 21, 24, 15, and 12 wk of age, respectively. Males that were
21 wk of age or older at the time of light stimulation responded quicker to light stimulation than
did younger males.
Key words: broiler breeder, fertility, sperm production
2012 J. Appl. Poult. Res. 21:88–94
http://dx.doi.org/10.3382/japr.2011-00363
1
Corresponding author: [email protected]
Moyle et al.: BROILER BREEDER MALES
DESCRIPTION OF PROBLEM
The poultry industry has made tremendous
gains in increasing the rate of BW gain, feed
conversion, and muscling of broilers over the
past several decades. These gains have allowed
chicken to become very efficient at growth, but
this has come at a cost to reproductive efficiency. These intense selections for meat production
traits have negatively affected the reproductive
performance of broiler breeder parent stock
[1] while resulting in an increased appetite [2]
because of changes in appetite control [3]. In
addition, as geneticists continue their selection
programs for increased growth rate, the negative relationship between growth and reproductive performance will continue to be magnified
[4, 5]. This results in a continued management
problem for the commercial broiler industry.
Currently, the only tool that is available to
help offset the negative reproductive effects of
this intense genetic selection is feed restriction
of replacement breeders and of the parent stock.
Feed restriction programs for broiler breeders
have been shown to delay sexual maturity [6,
7], increase livability [6, 8, 9], and increase fertility and hatchability in broiler breeder males
[10–12].
Although several older reports indicated that
feed restriction of breeder males could be accomplished with little to no effect on fertility
and hatchability [13–15], this may not be necessarily true with the modern broiler breeder male.
Scogin et al. [16] reported that when cockerels
were fed increased feed allotments, there was
a significant increase in sperm cell numbers
and semen volume as compared with a control
group. This is important because as growth rates
continue to improve, males are placed under
increasing stress to achieve the recommended
target BW while not sacrificing important reproductive traits.
Feed restriction is typically initiated at between 1 and 3 wk of age, along with a restriction
of light to control the day length to delay sexual
maturity. Yu et al. [17] found that feed allocations during the rearing phase are typically 60
to 80% less than what the birds would consume
under ad libitum feeding conditions, whereas
Savory et al. [18] reported that during the laying period, birds consumed 25 to 50% less than
89
they would if fed ad libitum. This practice results in a reduction of BW in adult breeders of
approximately 45 to 50% compared with that attained under ad libitum feeding conditions [19].
Although feed restriction has important welfare
benefits, such as increased reproduction, fewer
leg problems, and less mortality and obesity,
there is also mounting evidence that feed restriction has negative effects on the welfare of broiler breeder males [20]. Among these negative
effects are rapid consumption of food allotment
[21, 22], expression of behaviors indicative of
extreme boredom and feeding frustration [23–
25], and, according to some reports [26, 27], increased aggression as compared with males fed
ad libitum. Although these effects may appear to
be negative, the overall welfare of the male has
been shown to be improved by feed restriction.
Benefits resulting from feed restriction include
fewer bone, joint, and foot problems; improved
tendon elasticity at an older age; improved antibody responses and disease resistance; and
lower mortality [20].
This feed restriction and the restriction of
growth are occurring at the same time reproductive systems are developing [28]. In addition,
previous research by Kirby [29] has shown that
when males are fed ad libitum, they can become
sexual mature as early as 12 wk of age. McCartney [30] found that males could produce semen
as early as 11 wk of age. This is much earlier
than the current practice of photostimulating
males at approximately 21 wk of age; therefore,
it may be possible to photostimulate males at an
earlier age than is currently practiced.
Current lighting programs used in industry
are based on what is best for female reproductive performance. Therefore, the purpose of this
study was to determine whether current programs are best for the broiler breeder male, or
if a shorter growing period and a faster rate of
BW gain would be more advantageous. Shorter
growth cycles would help to lower the stress of
feed restriction and possibly allow for improved
welfare during the rearing stage.
MATERIALS AND METHODS
Day-old Cobb (parent stock) [31] broiler
breeder male chicks were placed and reared at
the University of Arkansas Research Farm. The
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JAPR: Research Report
Figure 1. Body weight targets before light stimulation for the 5 treatment groups used in this study. Age of males at
light stimulation was 24 wk for the T24 group, 21 wk for the T21 group, 18 wk for the T18 group, 15 wk for the T15
group, and 12 wk for the T12 group. n >100 males/treatment.
chicks were placed in allotments of 125 cockerel
chicks per treatment group (625 birds in total)
and were staged 3 wk apart over a 12-wk period. This allowed all treatment groups to reach
the target BW of 3,060 g at the same time (same
calendar date) and be ready for simultaneous
light stimulation. To achieve a BW of 3,060 g
at the time of light stimulation, the target BW
in Figure 1 were used. These BW were determined by fitting a line from the average chick
weight at hatch to the target BW at the time of
light stimulation. The 5 treatment groups consisted of males that were 24 wk (T24), 21 wk
(T21), 18 wk (T18), 15 wk (T15), and 12 wk
of age at light stimulation (T12), respectively.
In addition, 800 Cobb-500 one-day-old pullets
were placed at the University of Arkansas Research Farm at the same time as the males in the
T21 group to provide hens for the natural mating
portion of the study. All treatments were fed the
same feed formulations for the duration of the
study; only the quantity varied during the rear-
ing period. Starter feed was used for the first 4
wk, after which the birds were fed a commercial pullet grower ration. Although it is accepted
that each treatment group of males may have
received differing quantities of starter feed, and
thus different levels of nutrients, this program
was used to try to maintain constancy in the feed
program where possible. Water was provided ad
libitum throughout the study.
The authors acknowledge that by placing
the males at 3-wk intervals, some variation
could have occurred because of differing parent
flocks. However, we speculated that the variation caused by the environment [32, 33] would
be much greater than that caused by potential
flock differences. Additionally, all efforts were
made to keep the breeder flock source of the
chicks obtained at or near the prime age (35 to
45 wk of age). During the rearing period, 5 random birds from each group were killed at the
day of placement and at 3-wk intervals up to and
including the time of light stimulation, where-
Moyle et al.: BROILER BREEDER MALES
upon the testes were removed and weighed to
determine development in relation to BW gains.
At the time of light stimulation, 120 males
(24 from each treatment group) were moved to
individual cages for the remainder of the study
for semen analysis. Five males were killed at this
time and the testes were removed for evaluation
of testicular development by size and weight
for birds from each treatment group at the time
of light stimulation. After light stimulation, semen was collected weekly from the individually
caged males and analyzed for semen volume, semen concentration, and sperm cell numbers. The
same technicians collected and analyzed the semen for the duration of the trial. Additionally, 5
males from each treatment group were killed at
2, 4, 8, and 12 wk after light stimulation, and the
testes were removed and weighed, as mentioned
previously. At the termination of the study (42
wk after light stimulation), all remaining males
were euthanized and the paired testes were removed and weighed.
All segments of this project complied with
the provisions of the Institute Animal Care and
Use Committee as specified by the Animal and
Plant Health Inspection Service, USDA, in 9
CFR Part 1(1–91).
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Data were subjected to ANOVA procedures
using JMP [34], with significance determined
between means with a P-value of <0.05.
RESULTS AND DISCUSSION
At the time of light stimulation, all treatment
groups had similar BW, with no statistical differences. Shank length was measured at this
time and used as an indicator of frame size, with
no statistical differences observed between the
treatment groups.
Testicular development before light stimulation was similar in all groups. All groups
showed an increase in testicular development 6
wk before light stimulation (Figure 2). We also
noticed that testicular weight as a percentage of
BW decreased during the first 3 wk of growth
in all groups, after which it leveled out and then
increased before light stimulation (Figure 3). In
all treatment groups, testicular weight increased
at about the same time before light stimulation,
indicating that testicular growth is affected by
nutritional level as well as BW and age.
At light stimulation, no significant difference
was observed in testicular weight between the
treatment groups; however, after light stimula-
Figure 2. Broiler breeder male testicular weight before light stimulation (n = 5 males/treatment from a total of n =
125/treatment group). Age of males at light stimulation was 24 wk for the T24 group, 21 wk for the T21 group, 18
wk for the T18 group, 15 wk for the T15 group, and 12 wk for the T12 group. An asterisk (*) denotes significant
differences (P < 0.05).
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Figure 3. Broiler breeder male sperm volume by age (n = 24 males/treatment). Age of males at light stimulation
was 24 wk for the T24 group, 21 wk for the T21 group, 18 wk for the T18 group, 15 wk for the T15 group, and 12
wk for the T12 group.
tion, testicular development was fastest in the
oldest 2 groups (T24, T21). Although the younger groups developed at a slower rate, groups
T18 and T12 had caught up by wk 4 after light
stimulation and T15 had caught up by wk 8 after light stimulation (Table 1). Therefore, males
that were older at the time of light stimulation
were more responsive to it. Younger males
were somewhat slower in their response but had
achieved similar testicular weights by the time
egg production reached the level at which eggs
are typically kept for hatching purposes. Thus,
although the response to light was slightly slower, it likely would not have negative effects on
fertility and may help prevent males from maturing too quickly and “slating the hens” once
placed in the production house.
The weights of the testes at the end of the
study are shown in Table 1. A significant difference in final testicular weight was observed,
with males from the T18 group having testes significantly larger than males from the T24, T15,
and T12 groups, whereas males in the T21 group
were not significantly different. Males that were
less than 18 wk of age at the time of light stimulation were not able to maintain testes as large
as those that were 18 or 21 wk of age at the time
of light stimulation. Males light stimulated at 24
wk of age also appeared to have smaller testes
compared with males light stimulated at 18 wk.
This is likely a result of the older male being
exposed to increased stress, in the form of feed
restriction, during rearing, which reduced their
long-term reproductive ability.
Table 1. Broiler breeder male testicular growth after light stimulation1
Group
At light
stimulation
2 wk
4 wk
8 wk
12 wk
41 wk
T24
T21
T18
T15
T12
1.44 ± 0.46
1.36 ± 0.46
0.77 ± 0.46
0.69 ± 0.46
1.09 ± 0.46
11.70 ± 2.36a
13.86 ± 2.36a
3.78 ± 2.36b
2.14 ± 2.36b
1.97 ± 2.36b
31.77 ± 3.75a
24.70 ± 3.75ab
27.46 ± 3.75ab
19.75 ± 3.75b
21.13 ± 3.75ab
29.11 ± 4.64
33.23 ± 4.64
34.93 ± 4.64
35.51 ± 4.64
23.15 ± 4.64
29.73 ± 3.43
26.33 ± 3.43
32.06 ± 3.43
34.47 ± 3.43
29.12 ± 3.43
27.54 ± 1.83bc
31.75 ± 1.59ab
34.93 ± 1.59a
26.39 ± 1.59c
27.03 ± 1.59c
a–c
Different letters in a column denote significant differences (P < 0.05).
Age of males at light stimulation was 24 wk for the T24 group, 21 wk for the T21 group, 18 wk for the T18 group, 15 wk for
the T15 group, and 12 wk for the T12 group. n = 5 per treatment for all ages except 41 wk, which had an n >34 per treatment.
1
Moyle et al.: BROILER BREEDER MALES
93
Table 2. Semen analysis of broiler breeder males light stimulated at various ages1
Treatment
T24
T21
T18
T15
T12
Volume,
mL
Billion
sperm/mL
Total no.
of sperm
0.306 ± 0.009b
0.274 ± 0.009c
0.460 ± 0.009a
0.291 ± 0.009bc
0.272 ± 0.009c
6.25 ± 0.077b
6.41 ± 0.077ab
6.48 ± 0.077a
5.76 ± 0.077c
4.95 ± 0.078d
1.92 ± 0.069b
1.75 ± 0.069bc
3.03 ± 0.070a
1.70 ± 0.070c
1.39 ± 0.069d
a–d
Different letters in a column denote significant differences (P < 0.05).
Volume is reported in milliliters per male. Each treatment had 24 males, and results shown are for the duration of the study.
Age of males at light stimulation was 24 wk for the T24 group, 21 wk for the T21 group, 18 wk for the T18 group, 15 wk for
the T15 group, and 12 wk for the T12 group.
1
Results from the collection and analysis of
semen are shown in Table 2. Overall, sperm
volume was highest from the males in the T18
group, followed by males from the T24, T15,
T21, and T12 groups, respectively. The significantly higher volume was due to the T18
males producing a higher weekly volume of semen throughout the majority of the production
period (Figure 3). Males from the T18 group
also had the highest sperm concentration and
produced the most sperm per ejaculate. Males
from the T12 group had the lowest sperm volume, sperm concentration, and total number of
sperm, whereas males from the T15 group performed only slightly better than those from the
T12 group but lower than the older males.
Allowing the males to grow somewhat faster
(18 vs. 21 wk of age at the time of light stimulation) during the rearing period can be beneficial
for lifelong sperm production. However, allowing the males to be light stimulated too early
appears to be detrimental because males light
stimulated at 15 wk or younger had lower sperm
volume, sperm concentration, and total number of sperm. Similar results were reported by
Pietsch et al. [35], who found that it was possible to light stimulate males and initiate sexual
maturation as early as 16 wk of age. The benefits of early light stimulation include a lower
feed cost and shorter housing time to produce
a male as well as lower stress caused by feed
restriction.
CONCLUSIONS AND APPLICATIONS
1. Testicular development before light
stimulation appears to be dependent on
several factors, including BW, age, and
level of nutrition.
2. Males that are more mature at the time
of light stimulation respond quicker to it
than do younger males, as measured by
testicular growth.
3. After 41 wk of production, males light
stimulated at 15 wk or earlier were unable to maintain testicular size when
compared with those light stimulated at
18 and 21 wk of age. Additionally, males
that were 24 wk of age at light stimulation had lower testicular weights.
4. Males light stimulated at 18 wk of age
had higher semen volume, sperm concentration, and total number of sperm
produced.
5. Males can be successfully light simulated at 18 wk of age without any negative
effects on reproductive performance.
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