Estimates of (co) variance components and direct and maternal heritability for growth traits in Santa Ines sheep breed

The objective of this work was to estimate the (co) variance components and direct and maternal heritability of the body weights of sheep of Santa Ines breed. A total of 3,771 lambs weights records of the Santa Ines hair sheep breed, progenies of 114 sires. and 758 ewes were analyzed, obtained from experimental herds of EMBRAPA - SNPA from 1985 to 1995. The covariance components and genetic parameters from additive genetic effects, maternal and permanent environmental effects, as well us the covariance between those effects for birth weight (BW), weight at 112 (W112) and weight at 196 days of age (W196), were estimated by Restricted Maximum Likelihood (REML) using MTDFREML program, under animal model. Including or not the maternal genetic effect or permanent environmental effect. as well as the generic covariance between the direct and maternal effects, five different animal models were used to determine the most appropriate model for each trait. In general, the most comprehensive model (Model 4) was the one that presented the greatest value for the maximum log likelihood function (log of L) for all studied traits. When maternal effects were excluded, estimates of direct heritabilities were substantially inflated (.31 to .37). The maternal effects were important for all traits, even those that were measured after weaning. Genetic correlation between direct and maternal effects for BW and W112 were negative anti low (from -.31 to -.10), however. for W196 this value was positive and high (from .67 to .98). The exclusion of the maternal effects, when they are important. resulted in overestimates of heritability.