DIFFERENCES BETWEEN SIRE GROUPS IN BODY MEASUREMENTS AND BODY WEIGHT CHANGES OF LACTATING COWS

Abstract

Body weights and measurements of 694 first, 519 second and 329 third lactation cows in five Research Branch herds of the National Cooperative Dairy Cattle Breeding Project of Agriculture Canada were studied. The A line cows were daughters of U.S., Canadian and Finnish Ayrshire proven bulls, Brown Swiss and Norwegian Red proven bulls and young Research Branch Ayshire bulls and Research Branch Ayrshire cows. Highly selected U.S. and Canadian Holstein proven bulls and young Research Branch bulls mated to Research Branch Holstein cows produced the H-line cows. The model for analysis contained fixed effects for station, year of birth, line, sire group within line and sire within sire group within line as classification variables and age at calving as a covariable. Sire group, line, station and sire had significant effects on all weights studied. However, most effects were not significant for weight changes. Daughters of Brown Swiss and Norwegian Red sires were nearly as heavy as the daughters of Holstein bulls. On average, cows lost about 20 kg of weight from calving to 56 days postpartum of first lactation. The older first calvers were found to lose more weight from calving to 56 days of first lactation and gain less weight from 56 days postpartum onward than the younger first calvers. The effects of station, line and age at calving were significant for most body measurements. Sire group effects were significant for 13 out of 24 measurements. Significant differences between sire groups existed in stature (withers height) at all lactations and ages. In contrast, body length (shoulder to hook) did not differ significantly between sire groups from 112 days of first lactation onward. Key words: Body weight changes, body measurements, dairy cattle