Variance component and heritability estimates for first and second lactation milk traits in the South African Ayrshire breed

For the estimation of additive and error variances and resulting heritability estimates 9 050 first and 5 541 second lactation records were used. Analyses were conducted using DFREML procedures. The heritabilities for first (and second) lactation for milk, fat and protein yield and fat and protein percentages were as follows: 0.342 (0.195); 0.332 (0.187); 0.296 (0.179); 0.451 (0.377) and 0.533 (0.464).