ESTIMATION OF VARIANCE-COMPONENTS AND PREDICTION OF BREEDING VALUES FOR SCROTAL CIRCUMFERENCE AND WEANING WEIGHT IN LIMOUSIN CATTLE

Variance and covariance components were estimated for yearling scrotal circumference and weaning weight from Limousin field data. Records of 8,226 bulls were used to evaluate 584 sires and 653 maternal grandsir es. Data included all herdbook records of bulls with a recorded scrota l circumference and their weaning contemporaries. Analyses were perfor med by restricted maximum likelihood techniques employing the expected maximization algorithm and fitting both single- and two-trait models. Scrotal circumference was first fitted in a single-trait, sire model to obtain starting values for variances for a later analysis. Likewise , weaning weight was fitted in a single-trait, sire-maternal grandsire model to obtain priors for (co)variances for a later analysis. Scrota l circumference and weaning weight were then fitted together in a two- trait model to estimate variance components. Estimates of variance com ponents were calculated. by equating (co)variances obtained from the m odels to their expectations. Estimates of heritability of scrotal circ umference, direct weaning weight, and maternal weaning weight were .46 , .25, and .19, respectively. Estimates of genetic correlations betwee n yearling scrotal circumference and direct weaning weight, scrotal ci rcumference and maternal weaning weight, and direct weaning weight and maternal weaning weight were .14, -.22, and -.44, respectively. The e stimate of the environmental correlation between scrotal circumference and weaning weight was .61. Genetic parameters obtained were then use d in two-trait, reduced animal mixed-model equations for a maternally influenced trait to predict breeding values for animals.