SYSTEMS OF MATING TO REDUCE INBREEDING IN SELECTED POPULATIONS

Stochastic simulation is used to compare different systems of mating t o reduce rates of inbreeding in selection programmes with phenotypic o r animal model best linear unbiased prediction (BLUP) evaluation. Comp ensatory mating (the mating between individuals from the largest selec ted families to individuals from the smallest) turns out to be proport ionately about 0.30 more effective than minimum coancestry matings for situations with low rates of inbreeding, such as phenotypic selection or high population size, although the advantage is less apparent if c ommon environmental effects are important. A modification of this syst em of mating is proposed which can be applied for overlapping generati ons, and this is shown to reduce rates of inbreeding proportionately b y about 0.50 more than for discrete generations. Under high inbreeding , however, such as for BLUP selection and small population size, minim um coancestry matings, or even avoidance of sib matings are more effec tive. A procedure combining compensatory and minimum coancestry mating s is also simulated and gives the largest reductions in the rate of in breeding. The effects of these and other systems of mating on the rate of inbreeding are shown to occur through a reduction in the cumulativ e effect of selection and a deviation from Hardy-Weinberg proportions.