FACTORS INFLUENCING LACTATION PERFORMANCE OF RANGE BEEF AND DAIRY-BEEF COWS

Abstract

An investigation was carried out to study factors influencing milk yields and milk constituents among range cows. June and September measurements of milk yield and constituent percentages of butterfat (BF), protein (PT) and lactose (LT) were taken using 206 and 222 cows in 1976 and 1977, respectively. The cows, representing four beef and dairy-beef breed groups, were from the University of Alberta beef herd and ranged in age from 2 to 10 years. Regression of milk yield on calf age (CA) demonstrated a negative association over the lactation period measured, although regression coefficients were not statistically significant. Associations between all constituent yields with CA were negative. However, regression coefficients of June and September constituent percentage variables on CA indicated a more positive association as lactation progressed. Cow weight loss during gestation, cow weight at calving and ADG during lactation did not account for a significant proportion of the variation in either milk or constituent yields or constituent percentages over and above main effects. The association between cow ADG during lactation and all yields was negative although not statistically significant. Calf birth-weight was positively associated with all yields, and showed negative association with BF% and PT%. Calf average daily gain measured from birth to September was highly associated with yields of milk and constituents, declining from June to September. Its association with BF% and PT% was negative. Cow calving interval was introduced as a possible factor influencing milk yields of 3- and 4-yr-old and mature cows. Its association with lactation performance was however, not significant. Key words: Lactation, range cows