Genetic environmental trends for first lactation milk traits in the South African Ayrshire breed

Estimated breeding values and genetic trends were obtained in Ayrshire cattle by using DFREML procedures for 9 050 first lactation records calving down from 1977 to 1992. Environmental trends were calculated as the difference between the phenotypic and genetic values. The Ayrshire breed showed a positive trend of 19 kg per year for milk yield, with similar trends for fat and protein yield, while the trends for fat and protein percentage were negative.