FACTORS AFFECTING PREWEANING PERFORMANCE IN BEEF CATTLE

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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.

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