Using Mating Programs To Control Inbreeding

dairy cattle breeding. Inbreeding decreases heterozygosity and increases the frequency of deleterious recessive genes, thereby reducing phenotypic performance and viability. This phenomenon, known as inbreeding depression, ultimately causes a decrease in dairy farm profitability. Inbreeding can be of particular concern for numerically small breeds that are making rapid genetic progress, such as Jerseys. Wiggans et al. found mean inbreeding coefficients of 3.3% for sire-identified U.S. Jersey cows born in 1990. However, many of these cows had incomplete maternal pedigree information, and the level of inbreeding may have been underestimated. Losses per 1% inbreeding were estimated at 21.3 kg (46.9 lbs.) milk, 1.0 kg (2.2 lbs.) fat and 0.9 kg (1.98 lbs.) protein per lactation in Jerseys. Breeders have traditionally tried to control inbreeding by avoiding matings of genetically related animals. However, as relationships within the breed increase, it becomes difficult to avoid such matings without the aid of a computer. Many bulls and cows that appear to be unrelated based on one or two generations of pedigree data are in fact closely related due to common ancestors in earlier generations. Therefore, computerized mate selection programs, which have traditionally been used for corrective mating of conformation traits, may have potential as a tool for controlling inbreeding. Although some existing mating programs consider inbreeding, this may not be done in an optimal manner. For example, some programs enforce an arbitrary maximum value for inbreeding of proposed matings, but there is little scientific evidence with regard to the choice of an acceptable level of inbreeding. In addition, some commercial mating programs use pedigree data from only the most recent generations, and this can lead to underestimation of inbreeding. The objective of this study was to examine the potential of several alternative mate selection strategies for the purpose of maximizing net profit and minimizing inbreeding in Jersey cattle.