A primary goal in dairy cattle breeding is to improve the profitability of milk production; hence, a sound dairy breeding objective should include all traits that are economically relevant in dairy production. In the past, breeding objectives for dairy cattle in most countries were focused solely on production traits. Significant changes, however, have taken place in recent years, gradually leading to more balanced breeding objectives comprising a wider range of economically important traits. Recently, there has been a need to apply these advances in knowledge to developing more comprehensive dairy cattle breeding objectives in South Africa. Hence, breeding objectives for Holstein cattle in South Africa were developed in the current study.
Economic values were calculated for those economically relevant traits that had adequate bio-economic data, namely milk volume, fat yield, protein yield, live weight, longevity, calving interval and somatic cell score (SCS). A bio-economic herd model for pasture-based and concentrate-fed systems in South Africa was used to calculate economic values by determining changes in profit arising from an independent unit increase in each trait. Alternative payment systems were used from four major milk buyers in South Africa. Relative economic values, standardized to the value of protein yield, were used to compare the relative importance of traits.
The results showed that protein yield and longevity consistently had positive economic values and the converse was true for live weight and calving interval. Economic value for volume was positive or negative, depending on whether the payment system rewarded or ignored volume. Sensitivity analysis showed that economic values were reasonably robust against fluctuations in the cost of feed and price of beef; with the exception of fat yield, whose value became negative when feed price exceeded R3.50 per kg DM. Generally, protein yield was the most important trait, although volume, longevity and SCS were more important in some situations. Surprisingly, calving interval was the least important trait, its value ranging from 4% to 22% of protein yield. Further work should focus on facilitating the wide adoption of these breeding objectives by industry.
In conclusion, this study identified a need to carry out routine genetic predictions for all traits included, in order to maximize the accuracy of genetic predictions. Economic values obtained in the study are fairly robust against changes in the prices of feed and meat; however, there is an apparent need to have objectives customized for payment or non-payment for volume. Further work is required to develop a more comprehensive model to improve calculation of the economic value of calving interval. The study points to large inadequacies in the previous selection index, the breeding value index for Holstein cattle (the well-known BVI); hence extensive efforts are required to facilitate the wide adoption by industry of the breeding objectives defined here.
Banga, C.B., Neser, F.W.C. & Garrick, D.J., 2014. Breeding objectives for Holstein cattle in South Africa. South African Journal of Animal Science 44, 199-214