Genetic response and inbreeding with different selection methods and mating designs for nucleus breeding programs of dairy cattle.

Stochastic simulation was used to study the effect of selection and mating strategy on rates of genetic response and inbreeding with a closed nucleus breeding program for juvenile and adult schemes with 8 males and 64 females selected to produce 1024 progeny (512 females). Selection strategies considered using all available information or only individual and sibling records. Selection of sires was either unrestricted or restricted to between full-sib families. The effect of avoidance of mating of relatives to limit inbreeding was also evaluated. Four mating designs were examined: each dam was mated to 1, 2, 4, or all sires. Mating designs involving one sire per dam and more than one dam per sire were referred to as hierarchical. Use of several mates per dam resulted in a factorial mating design. Selected parents were mated either randomly, best to best, or best to worst. An index based on relative inbreeding to response ratio was used to describe the effectiveness of strategies for reducing inbreeding relative to changes in rates of genetic response. Strategies that lower index values were preferred and include selection on BLUP or approximations of BLUP and factorial mating designs that involve the random mating of dams to several sires. Factorial mating designs were effective for a range of heritabilities. Avoidance of matings of full sibs and restriction of selection of sires to between full-sib families enabled appreciable reductions in the index. Nucleus breeding programs based entirely on the selection of juveniles were not indicated because they had higher index values than adult schemes.