The development of breeding objectives for Holstein and Jersey cattle in South Africa
Banga, Cuthbert Baldwin
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A sound breeding objective is the basis for genetic improvement in overall economic merit of animals. Breeding objectives for Holstein and Jersey dairy cattle breeds in South Africa were developed in the current study, using a systematic approach. First, a logical framework with a profit focus was utilised to develop plausible selection goals for the pasture-based and concentrate-fed dairy production systems in South Africa, leading to an exhaustive list of objective traits influencing these goals and subsequently their possible selection criteria. Next, economic values were calculated for those objective traits for which there was adequate bio-economic data, viz.: milk volume, fat yield, protein yield, live weight, longevity, calving interval and somatic cell score. A bioeconomic model, simulating typical South African pasture-based and concentrate-fed herds, was used to calculate economic values by determining changes in profit arising from an independent unit increase in each trait. Alternative payment systems of four major milk buyers in South Africa were used. Relative economic values, standardised to the value of protein, were used to compare the relative importance of traits across breeds, production systems and payment systems. Protein yield, fat yield and longevity consistently had positive economic values and the converse was true for body weight and calving interval. Economic value for volume was positive or negative, depending on whether the payment system paid for it or did not. Economic values were reasonably robust to fluctuations in the cost of feed and price of beef; with the exception of fat, whose value became negative beyond the feed price of ZAR3.50. Protein was, overall, the most important trait, although volume, live weight, longevity and somatic cell score were more important in some situations. Calving interval was the least important trait, its value ranging from 4 to 22% compared to that of protein, probably because the model used underestimated its value. Sire rankings on aggregate EBVs based on these economic values did not differ much across breeds, production systems and payment systems, most rank correlations falling in the range 0.70-0.99. A single breeding objective may therefore be used for both the Holstein and Jersey breeds, across the different production and payment systems. The basis for multiple-trait selection in the major cattle breeds in South Africa has thus been developed. Considerable work, however, needs to be done to enhance this breeding objective as well as facilitate its wide adoption by industry.