FACTORS AFFECTING PREWEANING PERFORMANCE IN BEEF CATTLE

Abstract

Two years data involving 176 and 201 cows from the University of Alberta beef breeding herd were used to study the influences on calf preweaning performance of: breed, age, weight, summer and winter weight changes and milk yield of dam; breed of sire; and birth weight, weaning age and sex of calf. All independent variables combined explained 73 and 70% of total variance in average daily gain (ADG) to weaning and 81 and 70% of total variance in weaning weight, respectively, for 1966 and 1967. Of all variables considered, milk yield had the greatest influence on preweaning performance, explaining about 60% of the variation in ADG to weaning and 40 to 50% of the variation in weaning weight. A 1-kg increase in daily milk yield resulted in an 11- to 14-kg increase in weaning weight. Breed of dam explained about 23% of total variance in ADG to weaning, most of which was accounted for by breed differences in milk yield. Breed-of-sire differences accounted for 5.7 and 1.4% of variance in ADG of progeny for 1966 and 1967 data, respectively. Male calves exceeded female calves in birth weight by 2 kg, in ADG to weaning by 0.03 kg, and in weaning weight by 8 to 9 kilograms. Birth weight was positively associated with calf growth rate. A 1-kg increase in birth weight resulted in 1.74- and 1.59-kg increases in weaning weight for 1966 and 1967, respectively. A 10-kg increase in post-calving weight of cow, independent of milk yield and cow age, resulted in approximately a 0.7-kg increase in weaning weight of calf. Average daily gain to weaning was influenced slightly more by cow age than by post-calving weight of cow. However, about 80% of the variation in ADG explained by either cow age or post-calving weight of cow was accounted for by differences in milk yield associated with either variable.