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Feeding Broiler Breeder Males. 2. Effect of Cumulative Rearing Nutrition on Body Weight, Shank Length, Comb Height, and Fertility¹

H. Romero-Sanchez^*, P. W. Plumstead, N. Leksrisompong and J. Brake^,2

^* Grupo Grica, Faculty of Agriculture, University of Antioquia, AA 1226 Medellin, Colombia; and Department of Poultry Science, College of Agriculture and Life Sciences, North Carolina State University, Raleigh 27695

² Corresponding author: jbrake{at}ncsu.edu

	ABSTRACT

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Two experiments were conducted to evaluate the effects of 2 planes (low and high) of cumulative nutrient intake during the rearing period on performance of broiler breeder males. The low cumulative nutrition program supplied 29,580 kcal of ME and 1,470 g of CP, whereas the high cumulative nutrition program supplied 33,500 kcal of ME and 1,730 g of CP to photostimulation at 21 wk of age. Two diets (LoDiet and HiDiet) were used with a single feeding program in experiment 1. In experiment 2, a single diet with 2 feeding programs (LoFeed and HiFeed) was used. In experiment 1, the 2 diets were blended from 21 to 24 wk to provide a gradual transition to a single common laying breeder diet that was fed during the production period. At 21 wk of age in experiment 2, males were divided into light or heavy BW groups to complete a 2 x 2 factorial design during the production period. The high plane of nutrition increased BW, shank length, and comb height during the rearing period, but the differences disappeared after 28 wk of age. Retrospective analysis showed that the heavy males at 21 wk of age in experiment 2 were also the heaviest males at 8 wk of age. Both low plane groups (LoDiet in experiment 1 and LoFeed in experiment 2) exhibited better fertility during late production. A cumulative nutrient intake during the rearing period of 29,580 kcal of ME and 1,470 g of CP was minimally sufficient for subsequent male reproductive performance.

Key Words: broiler breeder male • rearing nutrition • fertility • body weight • shank length

	INTRODUCTION

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Genetic selection has been successfully used by the broiler industry to improve expression of highly heritable traits such as BW, breast muscle yield, and feed efficiency. However, these genetic improvements may be accompanied by a decline in reproductive variables (Goerzen et al., 1996; Barbato, 1999) such as delayed sexual maturity and reduced fertility generally associated with excess BW (Siegel and Dunnington, 1985). Low density diets have often been used with broiler breeders to control excessive BW (Leeson and Summers, 1997, 2000). Although it has been shown that low CP diets fed to males during the rearing period has no effect on semen volume and spermatozoal concentration (Wilson et al., 1971; Vaughters et al., 1987), low ME intake during the production period is reported to be responsible for alterations in semen characteristics (Sexton et al., 1989a) and decreased fertility (Sexton et al., 1989b; Cerolini et al., 1995). It has also been demonstrated that there is a minimum cumulative nutrient intake of CP and ME required before photostimulation, irrespective of BW, in both females and males (Walsh and Brake, 1997, 1999; Peak, 2001). The objective of the present experiments was to feed broiler breeder males low or high planes of cumulative nutrition during the rearing period and study their physical attributes as well as subsequent reproductive performance.

	MATERIALS AND METHODS

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Rearing Management and Measurements

Two experiments were conducted to evaluate the effects of 2 levels (low and high) of cumulative CP and ME intake during the rearing period on fertility of commercially available broiler breeder males (Ross 344; Aviagen Inc., Huntsville, AL). In both experiments, day-old broiler breeder chicks were placed in a 20-pen growing house with 16 pens for females (Ross 308 SF) and 4 pens for males. Each 3.96 x 3.96 m pen was equipped with the equivalent of 750 cm of linear feeder space (6 tube feeders) and 2 automatic drinkers. At placement, there were 68 females and 50 males in each female and male pen of experiment 1, respectively, and 96 females and 88 males in each female and male pen in experiment 2, respectively. Access to water was limited by a time clock and solenoid system sufficient to control litter moisture and allow the birds to have unlimited access to water when feed was present. After exposure to 23 h of light per day for 1 wk, all birds were reared in a blackout house to 21 wk of age under an 8L:16D lighting program. Male BW and shank length were individually measured at 4, 8, 12, 16, and 20 wk of age during the rearing period, as well as comb height at 16 and 20 wk of age.

Experimental Diets and Feeding Programs

Two different cumulative feeding programs providing 29,580 kcal of ME and 1,470 g of CP or 33,500 kcal of ME and 1,730 g of CP produced the low or high planes of cumulative nutrition to 21 wk of age, respectively. In experiment 1, two grower diets (LoDiet and HiDiet; Table 1) were formulated to provide the 2 cumulative nutrition treatments using a single feed allocation program (Figure 1, panel A). From 21 to 24 wk of age, the LoDiet and HiDiet diets were proportionally blended to create a gradual transition to a single common breeder diet (2,930 kcal of ME/kg and 15.4% CP) that was fed during the production period in both experiments (Table 1). In experiment 2, during the rearing period, 1 single grower diet (Table 1) was used with 2 different feed allocation programs (LoFeed and HiFeed; Figure 1, panels A and B) to provide the same 2 cumulative nutrition programs that were supplied during experiment 1.

View larger version (14K): [in this window] [in a new window]   Figure 1. Male feeding programs during rearing (panel A) and production periods (panel B) in experiments 1 and 2. In experiment 1, Ross 344 males received a single feed program using 2 diets containing either low or high nutrient density. In experiment 2, a single diet was used with either low plane (LoFeed) or high plane (HiFeed) of feed allocation. Both experiments supplied the same cumulative nutrition to 21 wk of age.

In both experiments, birds were moved at 21 wk of age to a curtain-sided, slat-litter house where the photoperiod was extended with artificial light to 14 h and 15 h at 22 and 24 wk of age and to 15.5 and 16 h at 5 and 50% rate of lay, respectively. Supplemental light provided an intensity of 35 lx in the laying house during night hours. An average of 55 and 60 females for experiments 1 and 2, respectively, along with 6 males, were allocated to each of the 16 pens. Each breeder pen was equipped with two-thirds wood slats and one-third litter floors, 2 automatic drinkers, and four 12-hole galvanized nest boxes. In experiment 2, ninety-six males were divided according to BW at 21 wk of age within their respective rearing program into either light or heavy groups (i.e., approximately the lower and upper 50%). The BW of heavy males within the LoFeed treatment ranged from 2,775 to 3,270 g and within the HiFeed treatment ranged from 3,150 to 3,550 g. Light males within the LoFeed treatment ranged from 2,575 to 2,695 g and within the HiFeed treatment ranged from 2,765 to 2,975 g. Male and female mortality were monitored daily, and feed intake was adjusted to maintain the programmed daily feed allocation that was slowly increased during the production period, as described by Figure 1, panel B.

Male BW, comb height, and shank length continued to be measured at 24, 28, 32, and 36 wk of age, whereas BW was further determined at 40, 48, 56, and 64 wk of age in experiment 1. In experiment 2, male BW, comb height, and shank length were measured at 26, 29, and 38 wk of age, whereas BW was further determined at 44, 50, and 64 wk of age. Egg production was determined daily. Eggs were collected twice daily and stored in a cooler at 18.6°C and 70% RH until incubated. Eggs laid on the floor and slats were collected separately and not incubated. Incubation analysis was conducted from weekly or biweekly sets of 60 eggs per replicate pen. All unhatched eggs were opened and examined macroscopically for evidence of embryological development and fertility by a single experienced individual.

Statistical Analyses

The GLM procedure of SAS Institute (2001) was used to analyze the continuous variables of the broiler breeder data. The repeated statement of SAS Institute (2001) was used for BW, shank length, and comb height data when appropriate. A 1-way design was conducted to analyze all data of experiment 1 and the rearing period data of experiment 2. For the production period of experiment 2, a 2-way arrangement of treatments was used, with the rearing feeding program (LoFeed or HiFeed) and the BW classification (light or heavy) as main factors. Pen was the experimental unit and, during the rearing period, 2 treatments were randomly assigned to each of 4 pens, whereas in the production period, 16 pens were divided among 2 or 4 treatments with 8 or 4 replicates per interaction cell for experiments 1 and 2, respectively. The fertility data were analyzed on a cumulative and age-based quartile period basis (Walsh and Brake, 1997), and data were analyzed as categorical data (Walsh and Brake, 1999), where each individual egg was taken as a binomial event, either fertile or infertile, using the general model (GENMOD) procedure of SAS Institute (2001). Orthogonal contrasts were used to compare treatment probabilities (Giesbrecht and Gumpertz, 2004). To test the age effect and its interaction with the treatments, a split plot design with time and its interactions in the subplot unit was conducted using PROC MIXED of SAS Institute (2001). Means were partitioned using LSMEANS, and statements of statistical significance were based upon P < 0.05 unless otherwise stated.

	RESULTS

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Growth and Physical Attributes

The effect of 2 planes of cumulative nutrition during the rearing period on male BW is shown in Figure 2. The high plane of nutrition, produced either by diet (HiDiet) in experiment 1 or feeding program (HiFeed) in experiment 2, significantly increased male BW during the rearing period (Figure 2, panels A and B), but no significant effect was observed after 24 or 26 wk of age in experiments 1 and 2, respectively. Heavy males selected at 21 wk of age were already significantly heavier than their pen mates at 8 wk of age (Figure 2, panel C). The heavy BW males maintained significantly higher BW up to 38 wk, but differences disappeared thereafter. The effect of the rearing plane of cumulative nutrition (either due to diet or feeding program) and male BW classification at 21 wk of age on shank length and comb height is shown in Figures 3 and 4, respectively. The low plane of rearing nutrition resulted in males with shorter shanks (Figure 3, panels A and B) and shorter combs (Figure 4, panels A and B) during the rearing period, but differences were no longer observed after 28 wk of age in either experiment. The heavy BW male group exhibited longer shanks at 8, 16, and 20 wk of age and greater comb height at 16 and 20 wk of age.

View larger version (12K): [in this window] [in a new window]   Figure 2. Male BW as affected by feeding program during the rearing period in experiment 1 (panel A) and experiment 2 (panels B and C). Ross 344 males were provided low or high planes of nutrition with either 2 diets (LoDiet and HiDiet in experiment 1) or 2 feeding programs (LoFeed and HiFeed in experiment 2). Males were classified as being in the 50% light or 50% heavy groups at 21 wk of age in experiment 2. An asterisk (*) represents a significant difference (P < 0.05). Transition period in panel A indicates when the LoDiet and HiDiet were blended in various proportions in experiment 1.

View larger version (14K): [in this window] [in a new window]   Figure 3. Male shank length as affected by feeding program during the rearing period in experiment 1 (panel A) and experiment 2 (panels B and C). Ross 344 males were provided low or high planes of nutrition with either 2 diets (experiment 1) or 2 feeding programs (experiment 2). Males were classified as being in the 50% light BW and 50% heavy BW groups at 21 wk of age in experiment 2. An asterisk (*) represents a significant difference (P < 0.05). Transition period in panel A indicates when the LoDiet and HiDiet were blended in various proportions in experiment 1.

View larger version (14K): [in this window] [in a new window]   Figure 4. Male comb height as affected by feeding program during the rearing period in experiment 1 (panel A) and experiment 2 (panels B and C). Ross 344 males were provided low or high planes of nutrition through either 2 diets (experiment 1) or 2 feeding programs (experiment 2). Males were classified as being in the 50% light BW and 50% heavy BW groups at 21 wk of age in experiment 2. An asterisk (*) represents a significant difference (P < 0.05). Transition period in panel A indicates when the LoDiet and HiDiet were blended in various proportions in experiment 1.

The effect of the male rearing cumulative nutrition on percentage fertility for experiment 1 is shown in Table 2. Fertility decreased after 36 wk of age (second quartile period), but the LoDiet treatment males exhibited less decline in fertility. The effect of the rearing feeding program and BW classification on fertility for experiment 2 is shown in Table 3. The decline in fertility was less than in experiment 1 and occurred later (after 46 wk of age). Nevertheless, in a manner similar to that of experiment 1, the decline was less in the LoFeed plane of cumulative nutrient intake group. Overall, in both experiments, the low plane of nutrition (LoDiet or LoFeed) improved cumulative percentage fertility (Tables 2 and 3, respectively). On the other hand, the male BW classification used in experiment 2 did not produce a significant fertility effect. However, a significant interaction between rearing feeding program and male BW classification was observed during the fourth quartile period and on an overall basis when the heavy BW males exhibited the best fertility when subjected to the LoFeed rearing treatment but the lowest fertility when subjected to the HiFeed rearing treatment (Table 3).

	DISCUSSION

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It had been suggested that shank length could affect the intersexual cloacal distance during mating (McGary et al., 2003) and thus affect fertility, but no significant differences in shank length were observed after 28 wk of age (Figure 3) and no significant effects on fertility were found during the first quartile period. In a similar manner, comb height was significantly less during the late rearing period on the low plane of nutrition, but no differences were found during the production period in either experiment (Figure 4, panels A and B). Thus, transient differences in physical attributes observed during rearing may not necessarily carry forward into, nor influence, the production period. Although the heavy BW group in experiment 2 exhibited significantly greater comb height through 20 wk of age (Figure 4, panel C), these differences also did not appear to affect fertility performance, in agreement with a preliminary report that did not find differences in fertility among males classified by comb height (Romero-Sanchez et al., 2003). Although female Galliforms of many species have been shown to prefer males with well-developed combs because they are reliable indicators of livability (Rintamaki et al., 2000), male dominance status (Graves et al., 1985; Holder and Mongomerie, 1993), or both, it has also been reported that only with extremely low comb development would fertility problems become evident (Leonard and Zanette, 1998). Also, grouping males by BW could have decreased variability in this trait such that selection of males by females was not likely to occur within experimental units (pens).

Although high BW has been implicated to be the main cause of declining fertility (Hocking, 1990), McGary et al. (2003) did not find a correlation between fertility and male BW or spermatozoal penetration of ova in 2 different broiler breeder strains. However, less than adequate ME intake relative to BW during the production period has been shown to be responsible for poor semen characteristics (Sexton et al., 1989a) and decreased fertility (Sexton et al., 1989b; Cerolini et al., 1995). Therefore, it seemed unlikely that BW per se directly affected male mating ability within the range of BW experienced in this study. In contrast, the present data suggest that males could be easily "overrestricted" at any number of times and stop mating then or later as a result of a deficiency of ME. The marked decline in fertility of the HiDiet males of experiment 1 after 45 wk of age was probably initiated by less than an adequate daily ME allocation early in the production period that was manifested by a plateau in BW near 28 wk of age (Figure 2). Such a delayed response has been shown to be possible with a bioenergetic model (Peak, 2001).

A significant interaction (P < 0.01), observed in experiment 2 during the fourth quartile period and cumulatively, showed that the heavy 50% BW males exhibited the poorest percentage fertility when reared on the HiFeed program but the best fertility when reared on the LoFeed program. It could be argued that these 2 groups of males were genetically similar but that males from the LoDiet group may simply have had lower maintenance requirements as they approached sexual maturity that would have made available extra nutrients (primarily ME) to support fertility. The effect of a deficient ME intake on BW can be easily observed if all males are routinely weighed, but the effects on fertility appear to be have been somewhat delayed. It can also be surmised that an appropriate increase in daily feed allocation would have easily met the ME requirements of the heavy BW-HiFeed combination group of males given that the overall difference in fertility in experiment 2 was small.

In conclusion, the data showed that a cumulative nutrient intake during the rearing period of 29,580 kcal of ME and 1,470 g of CP resulted in a broiler breeder male of adequate size with adequate cumulative nutrition at 21 wk of age to be able to maintain good fertility throughout the production period if fed appropriately therein. However, greater nutrient intake and BW during rearing could probably be successful with appropriate adjustments in daily nutrient allocation after photostimulation.

	FOOTNOTES

 
¹ The use of trade names in this publication does not imply endorsement of the products mentioned nor criticism of similar products not mentioned.

Received for publication May 25, 2006. Accepted for publication September 9, 2006.

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