COMBINING THE GENETIC AND CLONAL RESPONSES IN A CLOSED DAIRY-CATTLE NUCLEUS SCHEME

Designs testing clones in a closed nucleus, in which 1024 cotes are tested each year, were compared for their additive genetic I response to selection (genetic response) and their genetic superiority of female genotype(s) selected for commercial cloning (clonal response), using stochastic simulation. clones were tested at the expense of dam or sire families, matings per dam (sire), or full-sibs per family. The reference design maximized the genetic response corrected for inbreeding in the absence of cloning. The trait considered teas overall economic merit for milk production, which was simulated assuming an approximate infinitesimal model with both additive ive and dominant gene action. Bulls and cows eligible for breeding were selected on their animal model estimated additive genetic effect at either 15 or 27 months of age. Female genotypes eligible for commercial cloning were selected on their estimated total genetic effect at 27 months of age. All (fe)male full-sibs were available for selection. With only additive gene action, testing clones at the expense of sire families, matings pel darn or full-sibs per family reduced genetic response, while it increased clonal response and inbreeding. Testing clones at the expense of dam families, however added to both the genetic and clonal response without increasing inbreeding. When eight clones were tested at the expense of dam families, the genetic response and the final genetic level of commercially available cloned embryos were maximal, Accuracy of clonal selection equalled 0.83. With dominant gene action, however, testing two clones at the expense of dam families maximized the final genetic level of cloned embryos, il respective of the level of inbreeding depression (accuracy of 0.72). Reliable commercial clone lines can be produced now and in future generations by testing clones at the expense of dam families.