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 ma ting strategy on rates of genetic response and inbreeding with a close d nucleus breeding program for juvenile and adult schemes with 8 males and 64 females selected to produce 1024 progeny (512 females). Select ion strategies considered using all available information or only indi vidual and sibling records. Selection of sires was either unrestricted or restricted to between full-sib families. The effect of avoidance o f matings of relatives to limit inbreeding was also evaluated. Four ma ting designs were examined: each dam was mated to 1, 2, 4, or all sire s. 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 r esulted in a factorial mating design. Selected parents were mated eith er randomly, best to best, or best to worst. An index based on relativ e 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 an d include selection on BLUP or approximations of BLUP and factorial ma ting 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 sir es to between full-sib families enabled appreciable reductions in the index. Nucleus breeding programs based entirely on the selection of ju veniles were not indicated because they had higher index values than a dult schemes.