Genetic parameter estimates for serum insulin-like growth factor I concentration and performance traits in Angus beef cattle.

Data for this study were obtained from an experiment involving divergent selection for blood serum IGF-I concentration in beef cattle. Multiple trait derivative-free REML procedures were used to obtain genetic parameter estimates for IGF-I concentration at d 28, 42, and 56 of the postweaning period and for mean IGF-I concentration, as well as for weights and gains. Included in the analysis were 1,563 animals in the A-1 matrix, 731 of which had valid records for mean IGF-I concentration. Direct heritabilities (hd2) were .42 +/- .13, .53 +/- .15, .71 +/- .16, and .48 +/- .13 for IGF-I at d 28, 42, and 56 of the postweaning period and for mean IGF-I, respectively. Heritability of maternal genetic effects (hm2) ranged from .02 to .12, whereas the proportion of the total variance due to the maternal permanent environmental effect (c2) was essentially zero for all measures of IGF-I. Genetic correlations of IGF-I with weaning and postweaning weights and with postweaning weight gain ranged from -.21 to -.54 and averaged -.38. The environmental correlation between IGF-I and performance traits varied from .10 to .35 and averaged .22. Phenotypic correlations of IGF-I concentrations with weaning weight and postweaning weights and gains ranged from -.01 to .12 and averaged .04. Estimates of hd2 indicate that it should be possible to change IGF-I concentration in beef cattle via selection. Negative genetic correlations imply that, if the goal is to make genetic improvement in weaning weights, postweaning weights and (or) postweaning gain in beef cattle, selection should be for decreased postweaning serum IGF-I concentration.