Analysis of feed intake of individually fed beef bulls using random regression models

To estimate genetic parameters for weekly feed intake (FI) of beef bulls records of FI on Bonsmara bulls (n = 3 012) for 5 years were analyzed using random regression model (RRM). The model included the fixed linear regression of cumulative feed intake on third order orthogonal Legendre polynomials (OLP) of the actual days on test (d 7 to 84 weekly) for starting age group and contemporary group effects. Random regressions on third order OLP were included for additional random effect of weaning-herd-year (WHY) effect and additive genetic effect of the animal and on fourth order for the additional random permanent environmental effect of the animal. The residual effects were assumed to be independently distributed with heterogeneous variance for each measurement period. The first additive geneticeigen function (with 95.6% additive genetic variance contribution) revealed that selection for decreased cumulative FI at any test day would tend to decrease cumulative feed intake throughout the test and vice versa. Random regression model could be used in genetic evaluation of cumulative feed intakes of individually fed beef bulls in South Africa.