Genetic evaluations of dairy sires across countries are becoming available. This has implications for the selection and use of bull sires, both within and across countries. An algorithm has been developed to maximize the net genetic response from bull sire selection across countries (combined selection), allowing for reduction in genetic variation and depression in performance due to inbreeding. Differences between countries in their genetic means, size (number of young bulls tested per generation), and breeding objectives and in the breeding horizon used, were considered. The effects of these factors were investigated for two countries. A population with a lower genetic mean improved quickly and within 2 to 3 generations contributed bulls to the population with the higher genetic mean. Response in each country using combined resources was usually greater than response in each country using only its own resources. In populations of equal genetic mean and size, response was increased by 7 to 17%. In populations of unequal size the numerically smaller population tended to benefit most. The extra responses were reduced if the correlation between the breeding objectives was less than unity. With a genetic correlation less than 0.8, the populations diverged quickly and within few generations each country relied on its own bulls. With several countries involved the situation becomes more complex, but the same basic principles seem to hold, with further gains from combined selection at a diminishing rate.
|Number of pages||8|
|Journal||Journal of Animal Breeding and Genetics|
|Publication status||Published - Jun 1991|