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PRODUCTION, MODELING, AND EDUCATION |


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* 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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Key Words: broiler breeder male rearing nutrition fertility body weight shank length
| INTRODUCTION |
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| MATERIALS AND METHODS |
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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.
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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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| 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 |
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Received for publication May 25, 2006. Accepted for publication September 9, 2006.
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