Genetic parameters of growth curve parameters in male and female chickens

1. Individual growth curves of 7143 chickens selected for the form of the g rowth curve were fitted using the Laird form of the Gompertz function, BWt= BW0xe(L/K(1-e-kt)), where BWt is the body weight at age t, BW0 the estimate d hatching weight, L the initial specific growth rate and K the maturation rate. 2. Line and sex effects were significant for each parameter of the growth c urve. In males, L, BW0, age and body weight at inflection (T-I and BWI) wer e higher whereas K was lower than in females. Lines selected for high adult body weight had higher BW0 and BW1 whereas lines selected for high juvenil e body weight had larger estimates of L and lower estimates of T-I. 3. Data from 38,474 animals were included in order to estimate the genetic parameters of growth curve parameters in males and females, considering the m as sex-limited traits. Genetic parameters were estimated with REML (REstr icted Maximum Likelihood) and an animal model. Maternal genetic effects wer e also included. 4. Heritabilities of the growth curve parameters were moderate to high and ranged between 0.31 and 0.54, L, BW0 in both sexes and BWI in males exhibit ed significant maternal heritability. Heritabilities differed between males and females for BWI and T-I. Genetic correlations between sexes differed s ignificantly from one for all parameters. L, K and T-I were highly correlat ed but correlations involving BW0 and BWI were low to moderate. 5. Sexual dimorphism of body weight at 8 and 36 weeks and of L, K and T-I w as moderately heritable. Selection on growth curve parameters could modify the difference between sexes in precocity and thus in body weight at a give n age.