Bayesian Estimates of Genetic Relationships between Growth Curve Parameters in Shall Sheep via Gibbs Sampling

The objective of this study was to estimate variance components and genetic parameters for growth curve parameters in Shall sheep. Studied traits were parameters of Brody growth model which included A (asymptotic mature weight), B (initial animal weight) and K (maturation rate). The data set and pedigree information used in this study were obtained from the Animal Breeding Center of Iran and comprised 4020 growth curve parameters of lambs from birth to 400 days of age during 1982 to 2012. Marginal posterior distributions of parameters and variance components were estimated using TM program. The Gibbs sampler was run 300000 rounds and the first 60000 rounds were discarded as a burn-in period. Posterior mean estimates of direct heritabilities for A, B and K were 0.13, 0.15 and 0.19, respectively. Estimates of direct genetic correlation between growth curve parameters were 0.41, -0.30 and -0.31 between A-B, A-K and B-K, respectively. Residual correlations between growth curve parameters varied from -0.57 (between A-K) to 0.62 (between A-B). Also, phenotypic correlations between growth curve parameters varied from -0.48 (between B-K) to 0.30 (between A-B). The low estimates of heritability obtained in this study implies that although genetic selection could be partially affected on the growth curve parameters, much of the improvement in these parameters could be attained by improvement of production environment rather than genetic selection in this breed of sheep.