Combining use of embryo sexing and cloning within mixed MOETs for selection on dairy cattle

Abstract

Summary - Given the same overall number of transferred embryos, a comparison was carried out between adult mixed (ie with bull progeny-testing) MOET (multiple ovulation and embryo-transfer) schemes with embryo sexing only versus embryo sexing plus cloning of female embryos. In the former schemes, natural and ET (embryo transfer) animals were allowed to breed. In the latter schemes, each category of females (single born or cloned) was allowed to give birth either to new single animals (natural calvings) or to new clones (ET). The optimal structure (subpopulation sizes and corresponding selection pressures) in both schemes was derived algebraically by maximizing the predicted asymptotic annual genetic gains, assuming an infinite population but accounting for the Bulmer effect. Detailed presentation is given here for the case of embryo cloning (that of embryo sexing was dealt with in a previous paper). Schemes using the full reproductive capacity of a given genotype allowed by cloning were found to be superior (+5 to +10% ) when the number of live replicates per cloned heifer was moderate (3-5). They were even more superior for higher number of replicates (10-20). This trend was confirmed by Monte-Carlo inbreeding-free (for the sake of consistency with the model) simulations. Some Monte-Carlo simulations accounting for inbreeding effect were carried out until year 100 after starting the breeding schemes. With 5 replicates per clone, the ultimate annual rates of increase of inbreeding were found to be still reasonable (0.20 to 0.25%). Using 10 replicates per clone would substantially increase these coefficients (0.27 to 0.33%), while still generating higher observed genetic gains. Consequently, keeping only 5 replicates would seem to be a reasonable comprise between increases in F and in genetic gains.