Reproductive and aggressive behavior in male broiler breeders with varying fertility levels

Abstract

Differential male fertility in naturally mated broiler breeders appears to be an inadvertent negative result of genetic selection for growth and high yield. Identifying male behaviors that reliably indicate fertility could improve production while avoiding artificial insemination procedures. We hypothesized subfertile males to display less courtship, attempt more forced matings, and have smaller secondary sexual characters. An age-related decline in the frequency of reproductive display was predicted. Males individually housed with an average of 10 females from two primary broiler breeder strains ( n=30 males per strain; A and B) were studied at five age periods from 30 to 51 weeks of age. Male reproductive behavior was recorded for 30 min per male at each age period. Fertility was determined by visual examination of the blastodisc of fresh-laid eggs, and comb area was measured by digital image analysis. Body weight (BW) and relative testicular weight were measured at age period 5. Age and strain effects upon behavioral frequency and the level of fertility were analyzed by mixed model repeated measures ANOVA; Kendall correlations were used to determine linear relationships between the reproductive traits and fertility levels. Our results indicated that Strain A displayed more of courtship behavior, particularly wing flapping ( P<0.001) and waltzing ( P<0.05) than Strain B. Frequency of wing flapping ( P<0.05), waltzing ( P<0.001), cloacal contacts ( P<0.05), total forced mating behavior ( P<0.001), and aggression ( P<0.05) declined with age in both strains. The frequency of forced matings was higher in Strain A than in Strain B at age period 1 ( P<0.05), while Strain B mounted less frequently ( P<0.01) and displayed less total reproductive behavior ( P<0.05) by age period 3. Relative testicular weight was positively correlated with Strain A comb area ( P<0.01), total reproductive behavior ( P<0.05), crowing ( P<0.05), and wing flapping P<0.001). Total reproductive behavior ( P<0.05) and wing flapping ( P<0.01) positively correlated with Strain A fertility, therefore reproductive behavior may reliably indicate fertility in this strain. Unexpectedly, reproductive display positively correlated with the frequency of forced mating behavior as well ( P<0.05). Heavier Strain B males displayed less total reproductive behavior ( P<0.05), therefore may face physical limitations on their ability to display high-intensity courtship.