Estimates of covariance functions for growth of Angus cattle from random regression analyses fitting B-spline functions

Estimates of variance components and genetic parameters for growth of Angus cattle from birth to 820 days of age were obtained from a random regression analysis. Trajectories were modelled through quadratic B-spline functions with 7 random regression coefficients for direct genetic and permanent environmental effects, and 5 coefficients for the corresponding maternal effects. Data comprised a large set of field records, selecting only animals with at least 4 weights recorded. Results showed smooth estimates of variances, increasing with weight and age, with good interpolation for early ages with few records and little end-of-range problems at the highest ages. On the whole, estimates of genetic parameters were consistent with literature results. However, estimates of heritabilities for weaning weight were higher for direct and lower for maternal effects than usually found, indicating a different partitioning between direct and maternal variances in random regression analyses than in standard multivariate analyses.