Evaluation of Ontario Holstein Dairy Sires for Milk and Fat Production

Abstract

Milk and fat production records of 176,380 Ontario 2-yr-old Holstein cows from 1958 to 1972 were used to evaluate 433 Holstein sires. The objectives of the study were to utilize the sire comparison procedures currently used in the northeastern United States on Ontario Holstein data; to determine feasible strategies of grouping sires to account for genetic trend; to re-evaluate heritabilities for milk and fat production while simultaneously evaluating sires; and to measure genetic progress through change in weighted average of sire proofs over years. The two grouping strategies were years in which first daughter record appeared in the data and artificial insemination stud ownership by years of appearance of first daughter record. Sire proofs based on many progeny were essentially the same in either grouping procedure, but young bulls with less than 20 progeny differed considerably. Due to the structure of artificial insemination units in Ontario, unit differences were nonsignificant. Estimates of heritability for milk and fat yield were .29 and .28. The change in weighted average of sire proofs per year was 20.9kg for milk and .63kg for fat production.