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2004 Poultry Science Association, Inc.
End-of-Season Carcass
and Reproductive Traits in Original
and Replacement Male
Broiler Breeders
N. J. Wolanski,* R. A. Renema,* F. E. Robinson,*,1 and J. L. Wilson†
*Department of Agricultural, Food and Nutritional Science, University of Alberta,
Edmonton, Alberta, Canada, T6G 2P5; and †Department of Poultry Science,
University of Georgia, Athens, Georgia 30602
Primary Audience: Hatching Egg Producers, Hatchery Specialists, Researchers
SUMMARY
Reproductive efficiency of male broiler breeders declines toward the end of a production cycle.
It is common to add young, replacement males (spiking) to a breeder flock to maintain or increase
fertility. To date, no study has reported if there are differences in the carcass and reproductive
morphology between original and spiked males at the end of the breeding period. In this study,
the weight, fleshing traits, footpad condition, and testes size of 327 Hubbard males (237 original
and 90 replacement) from a commercial operation were examined. The original birds (63 wk of
age) had significantly higher BW, breast weight, girth measurement, keel length, and spur length
than the spiked males (48 wk of age). While external indicators of size and fleshing differed between
replacement and original roosters, testis weight was not affected by the age of the bird. It was
found that average testis weight correlated well with BW in birds in which testicular regression
had not taken place but only weakly with spur length. Because original males had a higher BW
and were more heavily fleshed than replacement males, their ability to successfully complete
matings may have been impeded. Further research is needed to link growth profiles with semen
quality, sexual behavioral, and longevity of a male breeder in a commercial flock.
Key words: broiler breeder males, replacement males, testis weight, testicular regression, fleshing
2004 J. Appl. Poult. Res. 13:451–460
DESCRIPTION OF PROBLEM insemination [4]. The reduction of fertility ob-
served in naturally mating flocks may be associ-
Broiler stocks have been intensively selected
for growth rate, feed efficiency, and breast muscle ated with increased BW of roosters toward the
mass. Genetic progress in these traits can impact end of lay [5] or a decrease in libido of older
reproductive fitness [1, 2]. Although female ef- males [6]. It has been suggested that the frequency
fects on a flock with poor fertility cannot be dis- of successful copulations may be reduced by car-
missed [3], the male most strongly influences cass characteristics, such as excessive chest girth,
fertility in the later stages of production. Flock which can lower flock fertility. Considerable vari-
fertility can be maintained with the use of artificial ability in reproductive performance between indi-
1
To whom correspondence should be addressed: frank.robinson@ualberta.ca.
452 JAPR: Research Report
vidual males [7] occurs with some males were managed according to standard Western Ca-
maintaining high rates of fertility, while other nadian industry conditions. Males were reared
males may be subfertile or infertile or may have sex-separate in light-tight housing with an initial
undergone testicular regression. photoperiod of 24 h light. On d 4, the day length
The use of external traits, such as BW, leg was reduced to 12.5L:11.5D until wk 4, when it
conformation, and secondary sex characteristics was further decreased to 8.5L:15.5D. At 17 wk
as indicators of male fertility in broiler breeders of age, 300 males were selected from the rearing
has been studied [8]. It was found that musculo- barn based on BW and were cohoused with 4,860
skeletal characteristics, rather than BW alone, are pullets. The flock was photostimulated at 23 wk
closely associated with a male’s ability to copulate with a single step increase in day length to
successfully. Recent research [9] has shown that 14L:10D. Day length was increased to 15L:9D at
low fertility toward the end of lay may be a result wk 26 and further increased to 16 h at 28 wk. At
of poor semen transfer due to males becoming 28 wk of age, an additional 45 males were added
too large to attain full cloacal contact with the from the original flock to replace mortality and
hens. Hocking and Duff [5] noted that increased to bring male numbers up to 6.8% of the hen flock.
male BW, which is common in late production, By 45 wk of age male numbers had dropped
was negatively correlated with fertility in naturally to 271 (6.2% of female flock). Ninety replacement
breeding flocks. Up to peak lay, the original males males were added to the original flock as part of
can maintain fertility. However, shortly thereafter the male spiking program. The new males were
fertility tends to decline. Hatching egg producers 30 wk old at the time of introduction to the mature
commonly supplement flocks with young, re- breeding flock and had been reared identically to
placement males at 40 to 45 wk of lay (spiking). the original males until 23 wk of age. However,
At the time of spiking, poorer performing original replacement males were kept in the rearing facility
males may then be culled. Addition of replace- at a photoperiod of 8.5L:15.5D until 30 wk of
ment males may improve or maintain the fertility age. Photostimulation (16L:8D) coincided with
of a flock. movement to the laying barn.
The first objective of this study was to deter- Both the replacement and original males were
mine if replacement males differ from original feed restricted from 2 wk of age until the end of
males in carcass characteristics (chest girth, keel production in accordance with the Hubbard BW
length, shank length, and spur length, BW, and guidelines. Two percent of the males were
testes weight) at the end of a production cycle. weighed every 4 d to obtain an average weight
The second objective was to study external fac- of the males then feed allocation was determined.
tors, such as footpad score and feathering score The males were reared on a grower ration with
within the original and the replacement groups, 2,620 kcal/kg ME and 17% CP. The male breeder
and to assess the impact of body size on these ration contained 2,660 kcal/kg ME and 16.1%
traits. The entire male population was divided into CP. Nipple drinkers provided the males with chlo-
LOW (<4,000 g), standard (STD) (4,001 to 4,900 rinated water, available ad libitum throughout
g), and HIGH (>4,900 g) BW categories and com- rearing and breeding. The University of Alberta,
pared within the original and replacement male Faculty of Agriculture, Forestry and Home Eco-
groups to assess the effect of relative body size nomics, Animal Policy and Welfare Committee
on carcass and reproductive traits. The impact of approved this experimental protocol, under the
BW on foot condition and reproductive status was guidelines of the Canadian Council of Animal
of particular interest, as well as the comparison Care [11].
of these traits between the original and replace-
ment males. Data Collected
MATERIALS AND METHODS Following removal of the hens from the barn
at 63 wk of age, all remaining males (n = 327)
Breeder Management
were wing-banded and sorted into the original (63
A commercial flock of 4,950 Hubbard Hi-Y wk of age) and replacement (48 wk of age) groups.
hens and 624 Hubbard Hi-Y males [10] (original) Visually, the original males had longer, sharper
WOLANSKI ET AL.: MALE BREEDER END-OF-SEASON TRAITS 453
spurs, while the younger replacement males had 5,200 g, whereas 33/237 or 13.9% of original
rounded, small smooth spurs. males had a BW of greater than 5,200 g.
The girth of the thoracic cavity was measured Fertility problems are associated with in-
on each live male with a fabric tape measure using creased male BW [15, 16]. As the original males
the notch of the keel as a reference point. The in the current study were heavier than the replace-
males were killed by cervical dislocation. A feath- ment males, their size may have contributed to a
ering score was assigned based on the relative decline in reproductive effectiveness later in the
feather cover of the bird’s back area using a 6- breeder period. Of the original males, 23.6% were
point scale described by Sikur et al. [12]. Footpad in the HIGH (>4,900 g) size category compared
condition was evaluated on a 3-point scale in with only 4.4% of the replacement males (Table
which a score of 1 was for poor footpad condition 2). More of the replacement males fit in the LOW
characterized by large, open sores or severe le- (<4,000 g) size category, with 40.0% of the birds
sions, a score of 2 for average footpad condition here compared with 14.3% of the original birds.
characterized by few open sores or swollen le-
sions, and a score of 3 for good footpad condition Breast Muscle and Fleshing Traits
characterized by little to no open sores or swol- The additional weight (477 g) of the original
len lesions. compared with the replacement males also im-
Birds were individually weighed, and the pacted the fleshing of the birds (Table 1). The
length of the shank and spur were recorded. The average breast muscle weight of the original group
breast muscle (pectoralis major and minor) and the was 678.4 g while that of the replacement males
testes were dissected from each bird and weighed. was 575.9 g (Table 1). This difference in breast
Any abnormalities, such as testicular regression, muscle weight similarly affected the chest girth
were recorded. A bird was considered to have and keel length measurements. The chest girth of
regressed testicles if the average testis weight of the original males was 3.9% greater than that of
the bird was less than 4 g. The birds were sorted the replacement males and keel length was 1.0%
into uniform body size groups around the mean greater (Table 1). Even when compared on a per-
flock BW to assess the impact of size on reproduc- centage basis, the breast muscle weight of the
tive traits in the original and replacement male original males (14.7%) was greater than that of
populations. The 3 BW groups were LOW the replacement males (14.0%). The data in Table
(<4,000 g), standard (STD) (4,001 to 4,900 g), 3 illustrate that breast weight, chest girth, and keel
and HIGH (>4,900 g), irrespective of whether length were significantly and positively correlated
birds were original or replacement males. The with BW (r = 0.88, 0.68, 0.56, respectively; P <
data were analyzed using SAS [13] with standard 0.001). These findings are in agreement with those
statistical methods [14]. of Bjerstedt et al. [17] who illustrated that breast
weight was highly correlated with BW in 62-wk-
RESULTS AND DISCUSSION old laying hens. Keel length also correlated well
BW with breast muscle weight (r = 0.52), indicating
that a larger keel length in a bird allowed more
The mean BW of the 327 males processed at space for breast muscle deposition, which may
63 wk was 4,442 g. The weights were normally be a result of indirect selection for breast muscle
distributed around this value (Figure 1A). Ap- mass in broiler offspring.
proximately 80% of the birds were within ±15% The older group of original males tended to
of the mean BW, suggesting that the flock was have more breast muscle deposition, which may
highly uniform in BW. However, when the total have a negative impact on mating ability. Previous
population was sorted into replacement and origi- research has related the decrease of fertility in
nal groups, the original males were found to be heavier males to an increase in breast fleshing,
significantly heavier than replacement males (Ta- which impedes the large-breasted males from at-
ble 1). The normally distributed subpopulation of taining full cloacal contact with females [5, 18].
replacement males represented a large proportion Genetic selection for growth traits has altered BW
of the lower end of the BW spectrum in this flock and muscle distribution of the broiler breeder,
(Figure 1B). No spiked birds had a BW of over with the frame of the birds also likely changing
454 JAPR: Research Report
FIGURE 1. Frequency of distribution of the total population (A) of 327 broiler breeder males and of the 90
replacement (48 wk of age) and 237 original (63 wk of age) males (B) sorted into 10 BW groups.
to carry the redistribution of muscle [9]. The When the original and replacement males
stance and leg dimensions of the male have been were sorted into the 3 BW categories, breast mus-
changing as breast muscle mass has increased, cle weight, chest girth, and keel length differences
which together may further affect the ability of followed the pattern of BW differences (Table 2).
the male to achieve cloacal contact during mating. The good correlation of breast muscle weight with
WOLANSKI ET AL.: MALE BREEDER END-OF-SEASON TRAITS 455
TABLE 1. Mean values (±SEM) for carcass and reproductive traits of original (63 wk of age) and replacement (48
wk of age) broiler breeder males
Parameter Original Replacement
n 237 90
BW (g) 4,573 ± 34a 4,096 ± 54b
Breast muscle weight (g) 678.4 ± 8.4a 575.9 ± 13.7b
(% of BW) 14.73 ± 0.11a 13.97 ± 0.18b
Chest girth (cm)A 39.8 ± 0.1a 38.3 ± 0.2b
Keel length (mm) 191.9 ± 0.5a 190.0 ± 0.7b
Abdominal fat pad incidence (%)B 21.94 ± 0.03a 12.22 ± 0.04b
Shank length (mm) 139.8 ± 0.4b 140.3 ± 0.7a
Spur length (mm) 23.7 ± 0.3a 13.9 ± 0.5b
Comb height (mm)C 66.3 ± 0.8 66.2 ± 1.3
Testes traits
Left testis weight (g) 15.9 ± 0.4 15.9 ± 0.6
Right testis weight (g) 14.1 ± 0.4 13.6 ± 0.6
Mean testis weight
(g) 15.0 ± 0.4 14.7 ± 0.6
(% of BW) 0.325 ± 0.008b 0.356 ± 0.012a
Means within a row with different subscripts are significantly different (P < 0.05).
a,b
A
Girth = bird circumference using notch of keel as reference point.
B
Birds possessing a discernable abdominal fat pad.
C
Height measured from top of head to tip of third spike from the front of the comb.
chest girth and keel length (Table 3) demonstrates While it may be assumed that the heavy birds
the usefulness of these noninvasive, external indi- had excessive breast muscle deposition, the low
cators of fleshing. Within the original males, the amount of fleshing observed in the LOW males
breast muscle of the HIGH, STD, and LOW males may also require attention. It is not known if these
represented 16.0, 14.6, and 13.3% of BW, respec- males were relatively low weight (and under-
tively (Table 2). The larger birds were carrying fleshed), when they entered the breeding barn, or
a significantly greater proportion of breast muscle. if their BW and condition deteriorated during the
While a similar relationship existed among the breeding period. During rearing, males that start
replacement male groups, the HIGH replacement out smaller or larger will typically remain at their
males carried a similar proportion of breast muscle end of the size distribution [19]. When males are
to the STD males. As the HIGH replacement subjected to the sperm quality index test, those
group contained only 4 birds, the means for this with scores in the lowest, most inferior quartile
group had a higher level of variance than the also have the lowest BW, while those in the upper
means for the lighter replacement males. The quartiles are statistically similar in BW [20].
breast muscle and fleshing traits for the original While differences in physiological measures of
and replacement males within a body size cate- male quality have been observed, elevated mating
gory appeared similar (Table 2). Overall differ- activity may have a more critical role in optimiz-
ences between the original and replacement males ing flock fertility [21]. The 2 extremes in male
presented in Table 1 were primarily due to there flock BW and fleshing are both problematic for
being few HIGH males within the replacement flock fertility.
male population, which skewed the results for
Abdominal Fat Pad
this population down. Body weight was the most
important affecter of breast muscle weight and Abdominal fat pads were not detectable in
fleshing traits. Increased breast muscle deposition the majority of the males. Whereas 21.9% of
was associated with age, with the older, original the original males had a visible abdominal fat
male population containing a higher proportion deposit, only 12.2% of the replacement males
of heavily fleshed, HIGH birds (Table 2). did (Table 1). This suggests that the older (and
456 JAPR: Research Report
TABLE 2. Mean values (±SEM) for carcass and reproductive traits of original (63 wk of age) and replacement (48
wk of age) broiler breeder males sorted on the basis of BW into 3 groups
Weight categoriesA
Parameter LOW STD HIGH
Original males
n 34 147 56
BW (g) 3,773 ± 45c 4,488 ± 22b 5,284 ± 35a
Breast muscle weight
(g) 504.4 ± 14.6c 655.1 ± 7.0b 845.2 ± 11.4a
(% of BW) 13.33 ± 0.25c 14.58 ± 0.12b 15.98 ± 0.20a
Chest girth (cm)B 38.0 ± 0.3c 39.5 ± 0.2b 41.8 ± 0.2a
Keel length (mm) 186.4 ± 1.1c 191.3 ± 0.5b 197.0 ± 0.8a
Abdominal fat pad incidence (%)C 35.3 ± 0.1a 19.1 ± 0.0b 21.4 ± 0.1ab
Shank length (mm) 135.3 ± 1.1c 139.7 ± 0.5b 142.8 ± 0.9a
Spur (mm) 22.5 ± 0.8b 23.3 ± 0.4b 25.5 ± 0.6a
Comb height (mm)D 65.6 ± 2.2 67.3 ± 1.1 64.2 ± 1.7
Testes traits
Left testis weight (g) 10.8 ± 1.0c 15.7 ± 0.5b 19.3 ± 0.7a
Right testis weight (g) 9.7 ± 0.9c 13.8 ± 0.4b 17.3 ± 0.7a
Mean testis weight
(g) 10.2 ± 0.9c 14.8 ± 0.4b 18.3 ± 0.7a
(% of BW) 0.272 ± 0.020b 0.329 ± 0.009a 0.347 ± 0.015a
Replacement males
n 36 50 4
BW (g) 3,655 ± 44c 4,342 ± 37b 4,986 ± 131a
Breast muscle weight
(g) 494.0 ± 14.1c 618.4 ± 11.9b 782.6 ± 42.2a
(% of BW) 13.41 ± 0.28b 14.24 ± 0.24a 15.69 ± 0.84a
Chest girth (cm)B 37.1 ± 0.2b 39.0 ± 0.2a 40.2 ± 0.6a
Keel length (mm) 186.5 ± 1.0c 191.7 ± 0.9b 199.8 ± 3.1a
Abdominal fat pad incidence (%)C 11.1 ± 0.1 12.0 ± 0.1 25.0 ± 0.2
Shank length (mm) 138.7 ± 1.1b 140.9 ± 0.9b 147.8 ± 3.3a
Spur length (mm) 12.7 ± 0.6b 14.6 ± 0.5a 16.9 ± 1.9a
Comb height (mm)D 64.6 ± 1.5 67.0 ± 1.3 70.3 ± 4.6
Testes traits
Left testis weight (g) 12.9 ± 0.9b 18.0 ± 0.8a 15.9 ± 2.8ab
Right testis weight (g) 11.0 ± 0.8b 15.4 ± 0.7a 13.9 ± 2.3ab
Mean testis weight
(g) 12.0 ± 0.8b 16.7 ± 0.7a 14.9 ± 2.5ab
(% of BW) 0.322 ± 0.020b 0.386 ± 0.017a 0.299 ± 0.060ab
a–c
Means within a row with different subscripts are significantly different (P < 0.05).
A
Divided into uniform groups around the mean flock BW. LOW = <4,000-g birds; standard (STD) = 4,001- to 4,900-g
birds; HIGH = >4,900 g.
B
Girth = bird circumference using notch of keel as reference point.
C
Birds possessing a discernable abdominal fat pad.
D
Height measured from top of head to tip of third spike from the front of the comb.
heavier) males may have begun to divert nutri- fat was not correlated with birds that had under-
ents from mating activities to storage. There was gone testicular regression within the LOW or
no significant effect of BW grouping on abdomi- any body size group, which would have been a
nal fat pad incidence in replacement males, possible explanation. However, to put the small
whereas 35% of the LOW, original males had (approximately 10 g) fat pad weights of males
a detectable fat pad compared with 19% of the in perspective, the mean fat pad weight of a
STD birds (Table 2). The presence of abdominal feed-restricted broiler breeder female at 54 wk
WOLANSKI ET AL.: MALE BREEDER END-OF-SEASON TRAITS 457
TABLE 3. Correlation coefficients (and P-values) of carcass and reproductive traits of original (63 wk of age) and
replacement (48 wk of age) male broiler breeders
Correlation coefficients (P-value)
Breast
Chest Keel Shank Foot muscle Mean testis
Parameter girthA length length scoreB weight weight
BW 0.6796 0.5633 0.3035 −0.2067 0.8822 0.4450
(0.0001) (0.0001) (0.0001) (0.002) (0.0001) (0.0001)
Chest girth 0.3894 0.2083 −0.0984 0.6616 0.2589
(0.0001) (0.0001) (0.076) (0.0001) (0.0001)
Keel length 0.3725 −0.1864 0.5247 0.1631
(0.0001) (0.0007) (0.0001) (0.0031)
Shank length −0.2732 0.2404 0.0501
(0.0001) (0.0001) (0.37)
Foot score −0.1857 −0.0916
(0.0008) (0.099)
Breast muscle weight 0.3147
(0.0001)
A
Chest girth was a measure of the birds circumference using notch of keel as reference point.
B
Evaluated on a 1 to 3 scale as follows: 1 = poor condition characterized by large, open sores or severe lesions; 2 = average
condition characterized by few open sores or swollen lesions; 3 = good footpad condition characterized by little to no open
sores or swollen lesions.
of age can be greater than 4.5% of the mature shown). Within the original and replacement
hen BW [22]. Male broiler breeders are feed male groups, 99.6 and 86.7% of the birds re-
restricted and have low circulating levels of es- ceived a score of 6, which refers to birds with
trogen, which virtually eliminates the coordi- no visible signs of bare skin on the back [12].
nated, dramatic increase in lipid synthesis driven Only 1 original male and 12 replacement males
by estrogen that occurs in the hen [23]. Without had lower than the top feather score. Within the
the stimulatory effects of estrogen on lipid depo- replacement male population, 10% of the birds
sition, the male remains very lean throughout received a feather score of 3, referring to birds
the first breeding cycle. with minimal feather cover on the back (6 to
30% feather cover) [12]. The inferior feathering
External Carcass Traits in these males appeared to be the result of in-
The replacement group had a mean shank creased feather picking, which may have been
length of 140.3 mm, which was significantly a consequence of establishment of a new social
greater than the 139.8 mm for the original group order from when these males were introduced
(Table 1). As both groups had achieved a mature to the barn. The feather scoring method used
frame size, the slightly longer shank length of was limited to examination of the back feathers
replacement males may be a reflection of their and did not assess feathering in the vent area,
later photostimulation age. Long bone growth which could have provided positive identifica-
generally ceases once reproductive hormone tion of sexually active males.
concentrations rise during sexual maturation. The raw footpad condition score was 2.13
There were several relatively tall individuals in in the replacement group compared with a mean
both the original and replacement groups. Shank score of 1.92 in the original group. Chi-squared
length increased in the heavier BW groups of analysis demonstrated that the distribution of
both the original and the replacement males (Ta- footpad condition scores in the original males
ble 2). Clearly frame size is a major component was shifted toward poorer values than in the
influencing mature BW. replacement males (Table 4). This may be a
The feather score analysis was not very use- result of replacement males spending less time
ful, as the majority of the birds received the in the breeding barn conditions or because they
highest score due to good feathering (data not were typically lower in BW than the original
458 JAPR: Research Report
TABLE 4. Foot scores of original (63 wk of age) and replacement (48 wk of age) broiler breeder males as groups
and sorted on the basis of BW into 3 groups at 63 wk of age
Foot scoreA
Source 1 2 3 1 2 3
(birds, n) (birds, %)
Male groupB
Original 85 86 65 36.02 36.44 27.54
Replacement 18 42 30 20.00 46.67 33.33
InteractionC
Original-LOW 8 14 12 23.52 41.18 35.29
Original-STD 53 50 43 36.05 34.01 29.25
Original-HIGH 24 22 10 42.86 39.29 17.86
Replacement-LOW 6 15 15 16.67 41.67 41.67
Replacement-STD 12 25 13 24.00 50.00 26.00
Replacement-HIGH 0 2 2 0.00 50.00 50.00
A
Evaluated on a 1 to 3 scale as follows: 1 = poor condition characterized by large, open sores or severe lesions; 2 = average
condition characterized by few open sores or swollen lesions; 3 = good footpad condition characterized by little to no open
sores or swollen lesions.
B
Original males had more birds with poor footpad scores (Fisher’s exact test P = 0.018). Original males total is 236 due to
missing data for 1 male.
C
Footpad scores not significantly different between original and replacement males for LOW (<4,000 g) (P = 0.74), standard
(STD) (4,001 to 4,900 g) (P = 0.13), and HIGH (>4,900 g) (P = 0.14) body size groups.
males. Body size may be an important factor in and replacement male groups (Table 2).
footpad score. While the footpad score distribu- VonSchantz et al. [25] reported that spur length
tions of original and replacement males within and testis mass were positively correlated. Spur
each body size group were not significantly dif- length was weakly but significantly correlated
ferent (Table 4), the original males included a with average testis weight within the original
greater proportion of HIGH males, of which male (r = 0.11) and replacement male (r = 0.20)
43% received a score of 1, indicating poor foot- groups. This relationship may be primarily a
pad condition. If the foot lesions or sores are result of BW.
severe, they may have a negative influence on The height of the comb did not differ be-
a male’s ability to mate. Lighter males would tween male groups (Table 1) or among body
place less stress on their footpads. Previous re- size classes within these groups (Table 2). Comb
search has shown that broiler footpad condition height did not correlate with reproductive traits
could be adversely affected if proper litter, venti- in this study and was not a useful indicator of
lation, and temperatures were not maintained in reproductive status. Comb height has previously
the barn [24]. been used as an indicator of testes weight and
The 237 original males had a mean spur fertility. However, a very diverse population
length of 23.7 mm, which was significantly may be required to see this effect, and it also
greater than 90 replacement males, with their appears to vary by strain [8].
mean spur length of 13.9 mm (Table 1). It is
clear that the spurs continue to grow within the Testis Weight
time frame of a typical breeding period. Within
the original and replacement male populations, The mean values of the left testis, right testis,
the LOW males had shorter spurs than either and average testis weight did not differ between
STD or HIGH males (Table 2). The HIGH origi- replacement and original males (Table 1). When
nal males had a significantly longer spur length comparing the testicular size of males within the
than the STD males, while it was only numeri- replacement and original groups, 13 of the 237
cally increased in the small group of HIGH re- original males (5.5%) had undergone testicular
placement males. There was a 3-mm difference regression, whereas only 2 of 90 (2.2%) replace-
in spur length between HIGH and LOW original ment males had regressed testes (<4 g). The fact
WOLANSKI ET AL.: MALE BREEDER END-OF-SEASON TRAITS 459
that a higher percentage of older males (original up a smaller proportion of BW than in the larger
males) had undergone testicular regression sug- body size groups. A similar comparison existed
gests that age may influence reproductive fit- between the LOW (12.0 g) and STD (16.7 g)
ness. It has been observed that more groups within the replacement males (Table 2).
seminiferous epithelium is atrophied in 160-wk Average testis weight was positively correlated
old male Japanese quail than in young quail, with BW (r = 0.445) (Table 3), further support-
suggesting an age-related decline in sperm out- ing the link between larger males and greater
put [26]. Hence, it may be likely that original absolute testis weights relative to smaller males.
males were experiencing testicular regression This is in agreement with the findings of Wilson
due to advanced age. Following testicular regres- et al. [28] who found that testis weight of males
sion, blood plasma testosterone concentrations was positively correlated with BW.
falls as the Leydig cells no longer produce high However, both Brown and McCartney [29]
levels of this sex hormone. This could explain and Wilson and McDaniel [30] have reported
why Duncan et al. [6] observed a significant that birds possessing larger testes did not pro-
decrease in male libido with age. Declines in duce the most semen. Nutrient intake can also be
male fertility are more likely to be due to the a factor in the maintenance of sperm production.
loss of effectiveness of specific individuals Bramwell et al. [3] reported that reduced energy
rather than to widespread declines in reproduc- diets contributed to reduced testes weights and
tive status.
resulted in the production of hatching eggs with
Overall, the left testis was on average 1.8 to
reduced fertility. Broiler breeder males main-
2.3 g heavier than the right in both original and
tained on a severe feed restriction program have
replacement male groups (Table 1). While this
been found to have a decreased semen volume
phenomenon has been shown to be true in mam-
mals as well [27], an explanation for this obser- and sperm concentration per ejaculate [31]. If
vation has not been reported. small males are being out-competed for access
Although there was no significant effect on to feed, there can be direct effects on the testes.
testis weight when the birds were sorted based Further complications in this relationship may
on age, there was a significant effect when these arise from factors, such as sperm mobility, in
groups were subdivided into the LOW, STD, which high mobility has been shown to improve
and HIGH BW groups (Table 2). None of the fertility but be associated with lighter males [32].
regressed males were in the HIGH body size Ultimately, mating behavior will determine the
group. Mean testis weight increased in the larger reproductive effectiveness of the male flock. En-
body size groups within the original males, aver- suring that the most reproductively active males
aging 10.2, 14.8, and 18.3 g in LOW, STD, and are also the most reproductively fit should be
HIGH males, respectively (Table 2). Within the an integral part of future breeder management
original-LOW males, mean testis weight made programs.
CONCLUSIONS AND APPLICATIONS
1. The primary difference between original and replacement males at the end of a breeding cycle
is BW.
2. Age had little effect on carcass traits within LOW or STD body size ranges. The characteristics
of original and replacement males in these categories were comparable. There were not enough
replacement-HIGH birds for an effective comparison to the originals.
3. Small males have less breast muscle mass, determined by live-bird fleshing measurements as
well as by necropsy at the end of the laying period.
4. Most male broiler breeders do not have a detectable deposition of abdominal fat at the end of
the breeding period.
5. Absolute testis weight did not differ between original and spiking males. However, there was
a trend to higher incidence of testicular regression in the former. Testes weights were highly
correlated with BW but only weakly correlated with spur length.
460 JAPR: Research Report
6. This study examined the relationship between male age and reproductive condition in a commer-
cial male population, as it is affected by body size. Further research is needed to link the long-
term impact of variation in juvenile and prepubertal growth curve on semen quality, sexual
behavior, and longevity of a male breeder in a commercial flock.
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16. Ogasawara, F. X., H. Abplanalp, and V. S. Asmundson. Acknowledgments
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turkey hens. Poult. Sci. 42:838–842. Randy Kasa from Kasa Farms is to be wholeheartedly acknowl-
17. Bjerstedt, H. L., F. E. Robinson, R. T. Hardin, and T. A. edged for donating his birds and assisting with the project. The
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