Genetic progress and inbreeding for alternative nucleus breeding schemes for beef cattle

Abstract

Alternative closed breeding schemes for beef cattle are analysed using stochastic computer simulation. Multiple ovulation and embryo transfer (MOET) schemes are compared with conventional schemes (schemes without MOET) with an equal expected number of progeny born per year. Schemes are compared for genetic gain and inbreeding obtained after 25 years of selection. The trait considered, evaluated in both sexes, has an initial heritability of 0·35. Different population sizes and numbers of sires selected are evaluated. Current realistic parameters for embryo production are assumed in MOET schemes.After 25 years of selection, and with no control on inbreeding, cumulative genetic gains are about 50% higher in MOET schemes compared with conventional schemes. The benefit from MOET is mostly due to increased selection intensities in females. The rate of inbreeding increases by up to nearly 300% when MOET is used. This maximum percentage increase in inbreeding following the use of MOET can be reduced to about 100% when selection and mating strategies for controlling inbreeding are used. The effect of the number of sires used on the inbreeding obtained is more important than the effect of the size of the herd. In MOET schemes, increasing the number of sires selected by a factor of three, leads to reductions in inbreeding rates of 40%. When schemes of the same size are compared at similar acceptable inbreeding levels, MOET schemes give around 30% higher genetic progress than conventional schemes.