Estimates of direct and maternal genetic parameters for weight traits and backfat thickness in a multibreed population of beef cattle

Variance components were estimated for weight at birth, weaning, and 365 d of age, and yearling ultrasonic backfat thickness in a multibreed populatio n of beef cattle. Data (n = 5880) were available on Fl animals and various crosses leading up to, and including, a composite breed (7/16 British, 1/4 Charolais, 1/4 Simmental, and 1/16 Limousin). Single- and two-trait analyse s were conducted using an animal model and derivative-free REML procedures. Covariates representing fractional contributions of each of the four pureb red groups and average heterotic effects, both direct and maternal, account ed for breed composition. Direct and maternal genetic, maternal per moment environmental, and residual effects were the random variables. Only minor d ifferences existed between parameter estimates obtained from the various an alyses. Mean direct heritabilities were 0.51, 0.33, 0.48, and 0.37 for weig ht at birth, weaning, and 365-d, and backfat, respectively, which, though w ell within the range of published estimates, seemed higher than average, in dicating diversity in the founding purebreds. Mean maternal heritabilites w ere 0.09, 0.13, and 0.08 for the three consecutive weights. A likelihood ra tio test showed maternal heritability and(or) the direct-maternal correlati on was important (P < 0.001) for 365-d weight. Averaged across weights, the direct-maternal correlation was 0.07, lacking evidence of genetic antagoni sm. No age of dam or random maternal effects on backfat were apparent. Phen otypic correlations between weight at birth and weaning and weight at weani ng and 365-d were 0.46 and 0.76, respectively. Though moderate between birt h and weaning weight, maternal genetic and permanent environmental correlat ions between weaning and 365-d weight approached unity, demonstrating mater nal carryover effects. Phenotypic and genetic correlations of 0.19 and -0.1 3, respectively, implied a limited association between 365-d weight and bac kfat, which possibly would have been stronger had far been measured later i n life. Estimates of variance components suitable for general use can be ob tained from data from multibreed animals by considering breed and heterotic effects.