POTENTIAL GENETIC GAINS IN DAIRY-CATTLE WITH GAMETE HARVESTING AND INVITRO FERTILIZATION

Potential rates of genetic response in dairy cattle with large numbers of gametes harvested per female were studied by deterministic simulation. A Juvenile Cross-classified design was proposed and tested: all males selected were mated to all females selected, generating numbers of paternal and maternal half-sibs. Candidates for selection were 13-mo-old juveniles, selected on the average of the estimated breeding values of their parents. The effect of selection on variance loss was accounted for. Restrictions on the minimum number of full-sib cells contributing parents were imposed to limit inbreeding, which was approximated accounting for the effects of selection on co-selection of sibs. The value of sexing embryos was studied. For a trait with 25% heritability in the base population and 15% coefficient of variation, annual responses and inbreeding rates were predicted at 3.7 and .81% with 500 females recorded and 4.4 and .32% with 50,000 females recorded. The response figures compare with 1.5 to 2.1% predicted for conventional progeny testing schemes. Embryo sexing had little effect. Many of the schemes provided further selection intensity within full-sib cells, which, with good indicator traits of useful marker-assisted selection, could add further response of over 1%/yr. Schemes mating sires x sires and dams x dams were also considered but contributed little further response.