The basic principles for maximising progress using the infinite alleles model are largely understood. However this is not the case when individual alleles can be identified in conjunction with continuous variation, nor when constraints on inbreeding are applied. Accounting for linkage disequilibrium does not alter the relative merits of progeny testing and MOET nucleus schemes. The reduction in the rate of progress at equilibrium in progeny testing is similar to the reduction in the total genetic variance. However in MOET nucleus schemes the reduction in progress is greater than the reduction in genetic variance alone since the value o f ancestral information is also reduced by linkage equilibrium. BLUP selection enhances progress and removes the distinctions between MOET nucleus schemes and progeny testing schemes. . When the female family size is increased, factorial mating gives extra progress when constrained by inbreeding. When accuracy is low, as in MOET nucleus schemes or the use of young unproven bulls indicator traits would prove useful. Cloning has potential for reducing genetic lags, but not as yet for increasing the progress o f leading herds; sexing of embryos and semen can improve progress through more effective use of the allocated resources.

John A Woolliams

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XIV. Dairy cattle genetics and breeding, adaptation and conservation., , 15–24, 1990
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