Description of lamb growth using random regression on field data

Random regression (RR) has been proposed as an accurate method for evaluation of growth data, however this method has seldom been applied to data from an extensive industry where few records per animal exist. Consequently, field data containing weight records of Poll Dorset sheep from 50 to 500 days of age were analysed fitting a RR model. This model included quadratic polynomials for direct genetic and environmental and maternal environmental effects, a linear polynomial for maternal genetic effects and heterogeneous error variances. Direct heritability estimates increased steadily throughout time and were in agreement with literature estimates taken at specific ages. Some estimates for the highest ages with with the least records were considered too high, in particular direct heritability beyond 450 days. Variances due to maternal effects were low throughout the trajectory. Results show that covariances between weights of sheep for a considerable range of ages can be modelled adequately through random regressions.