Genetic parameters for direct and maternal effects on weights and ultrasonic muscle and fat depth of lambs

Abstract Genetic parameters were estimated for liveweights, total weight gains and ultrasonic muscle and fat depth of lambs at two different ages using a single trait animal model including direct and maternal genetic effect, and an environmental effect. Records of 972 lambs descending from 60 rams and 295 ewes were analysed by DFREML procedures. The approximate sampling correlation between the estimates indicated that the variance components of the maternal genetic effect and the covariance between the direct and maternal genetic effects were the most difficult parameters to estimate precisely. The correlation between the direct and maternal genetic effects was close to zero (−0.10–0.04) for all traits. Direct heritability estimates for weight declined slightly according to age from 0.22 at birth to 0.12 at weaning. The heritability estimate on maternal effect was very high for birth weight (0.42), and slightly lower for pre-weaning weight (0.14) than for weaning weight (0.17). The direct and maternal heritability estimates for ultrasonic measurements were generally low, except for the direct heritability for muscle depth at weaning (0.32). The results indicate that selection for maternal ability will not be more efficient by including pre-weaning traits in the selection index.