Physical traits and reproductive success in male primary broiler breeders

Genetic selection for high yield in primary broiler breeder males may result in skeletal modifications that impede sperm transfer upon mating. In addition, fluctuating asymmetry (FA) in bilateral traits has been shown to reliably indicate male reproductive potential in some avian species. The goal of this study was to determine if physical variation due to genetic selection and FA could explain and predict differential fertility and semen quality in male broiler breeders. Sixty males from two primary broiler breeder strains (A and B) were individually housed with an average of 10 females. Fertility was estimated by examining the germinal disc (GD), and semen quality by counting sperm penetration (SP) through the perivitelline layer. At 50 wks, body weight (BW) was taken and males euthanized. Posterior pelvic length and width (PPL and PPW), dorsal pelvic length and width (DPL and DPW), tarsometatarsal length and width (TL and TW), and wattle length and width (WL and WW) were measured with digital calipers. Strain differences included BW (P<0.01), WL (P<0.0001), WW (P<0.0001), PPL (P<0.01) and DPW (P<0.001). The degree of FA in TL (P<0.05) and WL (P<0.05) was greater in Strain A, however FA did not correlate with fertility or SP in either strain. Strain A WL correlated with SP (r=0.295; P<0.05). There was a negative relationship between Strain A fertility and DPW (r=-0.298; P<0.05). Strain A DPW alteration may affect sperm transfer upon copulation, however, this correlation was weak and should be further investigated to validate the relationship between pelvic structure and copulatory success. Fertility and SP did not correlate with physical traits in Strain B. Strain differences demonstrate potential impact of selection on physical traits. A significant relationship between comb size and Strain A fertility has been previously shown, and the present study provides further evidence supporting evaluation of sexual traits as fertility indicators for Strain A.