Comparison of simulated and theoretical results in adult MOET nucleus schemes for dairy cattle

Abstract

Six discrete generation of single trait selection in a closed adult Multiple Ovulation and Embryo Transfer (MOET) nucleus breeding scheme in dairy cattle were modelled using Monte Carlo simulation. The six schemes simulated had 16, 32 or 64 dams and four or eight sires selected. A hierarchical mating design was used with four daughters and one son per dam. Response to selection ranged from 0.21 to 0.3 phenotypic standard deviations per generation. Selecting eight sires instead of four resulted in no loss in response, except with 16 dams, and brought about substantial reductions both in inbreeding and in the variance of response. Genetic gain was predicted by two deterministic models. The first, assuming infinite population sizes and base generation variances, overestimated simulated responses by 40–47% with eight sires and by 63–67% with four sures selected. The responses predicted by the second model, which accounted for the effect of finite population sizes on selection intensities and the effects of inbreeding and selection on genetic variances and accuracies of selection, were within 5% of the simulated responses. Simulated inbreeding rates were 4.2–4.8% and 7.4–7.9% per generation with eight and four sires selected, respectively. These values were 1.8–2.7 times higher than predicted by simple random selection formulae.