AN ANALYSIS OF THE CONTEMPORARY PRODUCTION OF ARTIFICIALLY AND NATURALLY SIRED CANADIAN HOLSTEIN–FRIESIAN COWS

Abstract

A study of first-lactation records, collected under Canadian Record of Performance and involving 12,815 Holstein–Friesian heifers by A.I. (artificial insemination) sires, and 13,543 Holstein–Friesian heifers by non-A.I. sires, within the same herds and season, revealed a superiority in average breeding value of 4.62 ± 0.48 B.C.A. (breed class average) for milk and 4.98 ± 0.50 B.C.A. for butterfat in favor of the A.I. sires. Expressed in terms of mature equivalent yield the superiorities were 248 ± 26 kg (546 ± 57 lb) milk; and 9.8 ± 1.0 kg (21.6 ± 2.2 lb) butterfat. The difference in butterfat test between the two sire groups was not statistically significant.The total volume of data examined consisted of 33,425 records of cows of all ages. Cows mated to A.I. sires were shown to be slightly superior, both in milk and fat production, to cows mated to non-A.I. sires [Formula: see text]. Adjustment procedures for this source of bias are discussed.Important seasonal differences were demonstrated, emphasizing the necessity of comparisons on a within-season basis.