Evaluation of genetic trends for traits of economic importance in South African Holstein cattle
Genetic evaluation for the South African dairy industry has kept pace with global advances in statistical methodology. Increasingly accurate estimated breeding values (EBVs), produced routinely in the past two or three decades, have aided selection decisions. This has been coupled with an increase in the number of traits officially recorded and for which EBVs are calculated. Currently, EBVs are routinely published for more than 20 traits for the major dairy breeds. The current study was conducted to assess the genetic trends realized for traits of economic importance in the South African Holstein population, for the period from 1983 to 2008. Performance and pedigree data of 1 231 930 animals were used to calculate EBVs for these traits by a multi-trait animal model. The resulting EBVs in turn were used to compute annual mean rates of genetic change. Genetic trends for yield decreased by approximately 57% during the decade from 1990 to 2000 and reached stasis in 2005 - 2007. Calving interval and somatic cell count also deteriorated over much or all of the period investigated. Given the widespread availability of genetic evaluations for these traits and the noted potential for selection to implement favourable genetic trends, development of strategies to improve the South African Holstein appears to be urgently needed.
Keywords: Calving interval, estimated breeding value, milk fat, milk protein, milk yield, somatic cell count