THE EFFECT OF IMPROVED REPRODUCTIVE-PERFORMANCE ON GENETIC GAIN AND INBREEDING IN MOET BREEDING SCHEMES FOR BEEF-CATTLE

The effect of improved reproductive techniques on genetic progress and inbreeding was investigated in MOET (multiple ovulation and embryo transfer) schemes for beef cattle. Stochastic simulation was used to model a closed scheme with overlapping generations. Selection was on a trait measured in both sexes, with heritability 0.35, and was carried out for 25 gears. The number of breeding animals was 9 sires and 18 donors. Embryo production was modelled using a Poisson distribution with the parameter distributed according to a gamma distribution. The mean number of transferable embryos per flush and per donor was 5.0, with a coefficient of variation of 1.28 and repeatability between flushes of 0.22. This model was compared with models used in previous studies (fixed number of embryos per flush or variable number of embryos but with zero repeatability between flushes). The coefficient of variation and the repeatability of embryo yield influenced inbreeding rates. The rate of inbreeding was underestimated by up to 17% when variability of embryo production was ignored. Without a constraint on the number of calves born per year, improved success rates for embryo collection and embryo transfer technologies led to notable increases in genetic progress. However, the rate of inbreeding was also increased with improved techniques. When the number of calves born per year was fixed, genetic progress was maintained but inbreeding rates were substantially reduced (by up to 11%) with improved techniques due to the opportunity of equalizing family sizes. There was no benefit from sexed semen with constrained number of calves per year.