Author: Sarah Louise Butson

Publisher: National Library of Canada

Published: 1981

Total Pages: 0

ISBN-13: 9780315059559

An investigation was carried out to examine trends in lactation performance and factors influencing milk traits and calf weaning weight among range beef cattle. Cows representing four beef and dairy-beef breeds and lines from the University of Alberta beef herds ranging in age from 2 to 10 years of age were used in the study. June and September measurements of milk and constituent percentages were taken on 206 and 242 cows in 1976 and 1977 respectively. Age and breed of dam, and age and sex of calf were recorded. Other variables examined were cow weight changes during gestation and lactation and birthweights, weaning weights and preweaning ADG of their calves. Milk variables and calf weaning weights were the traits studied. In Chapter I the lactation performance of the four breed groups of dams was examined. Results indicated that crossbred cows with dairy breed ancestry yielded more milk and were more persistent than a purebred traditional beef breed. Trends between breeds for constituent percentage production were less noticeable although the dairy crossbreds tended to produce less butterfat% than the purebreds. In Chapter II factors influencing milk and constituent yields were investigated using the multiple regression technique in Chapter II. Stepwise regressions involving age and breed of dam accounted for between 34.0% and 44.0% of the variance in any of the milk or constituent yields. Full and restricted regression models allowed the introduction of independent variables after adjusting for age and breed of dam effects. Calf preweaning ADG showed a high association with milk yield variables. Other factors such as calf birthweight and cow weight changes however did not account for a significant proportion of the variance in any one milk or constituent yield variable. Because associations and correlations between milk yield and calf ADG were significant but only moderately high, all factors influencing weaning weights of range calves were examined in Chapter III. Regression analysis indicated that age and breed of dam effects accounted for an average of 47% of the variance in calf weaning weight. When age and breed of dam were not considered, milk or constituent yields accounted for approximately 40% of weaning weight variance. However, milk variables still accounted for up to 10% of the variance after accounting for the effects of age and breed of dam. Calf birthweight and cow weight changes had minor effects on calf weaning weight. As a significant proportion of the variance in weaning weight was accounted for by milk variables, which in turn are largely a reflection of the breed of dam, it was concluded that selection for increased lactation performance and the introduction of dairy breeds into the breeding program of a beef herd can effect meaningful increases the weights of calves weaned.