Genetic improvement of livestock depends on defining breeding objectives and accurately identifying the right animals to be used for future breeding. The National Livestock Improvement Schemes serve as basis for accurate recording of economically important production traits. This data, combined with pedigree information from SA Stud Book, are used to accurately identify animals of superior value free of the usual bias associated with visual appraisal.
History of genetic evaluation of livestock in the RSA
Measurements on individual animals serve as early indicators of its genetic ability when compared to those of its contemporaries within the same group. The next logical step, especially in the case of dairy animals, was sire evaluation through progeny groups. This led to the utilization of contemporary comparison methods to estimate the breeding values of sires.
Although the objective is to "measure" the genetic ability of each potential breeding animal, most of these efforts had the problem that "true genetic" merit could not effectively be separated from environmental effects. A bold improvement in breeding value estimation occurred when mixed model methodology was introduced. Familial relationships between sires enhanced the accuracy at which breeding values were estimated because the effective separation of genetic merit from environmental effects became possible.
The limitations imposed by progeny testing were overcome when the animal model came into use. All measurements as well as pedigree information are taken into account when each individual's breeding value is estimated. The animal model was further enhanced when more traits were included in analyses and the genetic correlations amongst them were included.
Since the inception of the National Livestock Improvement Schemes, estimation of breeding values was based on individual measurements within contemporary groups. These comparisons still form part of all the schemes and serve as early indicators for more precise estimations. Breeders receive within herd and contemporary group performance indices for the different traits. Mixed models were first fitted to data in South Africa in the mid eighties on an experimental scale. Dairy animals were first to receive breeding values from BLUP methodology when the estimates from a Sire Model were supplied in 1987 but since 1992 complete animal models are fitted to dairy records.
Breeding values for beef cattle became a reality for stud breeders with the first animal model analyses of the local Drakensberger breed in 1993. This was followed by analyses for seven more breeds in 1994/1995 and the second run on three breeds.
Genetic evaluation of sheep started in 1986 with the analyses of the experimental Merino flock at Klerefontein, near Carnarvon. This was followed by single flock evaluation as part of post graduate studies and the evaluation of progeny groups of rams for the industry. Recently the first multiple trait animal model analyses for a sheep breed on a national basis anywhere in the world was completed for the Merino.