Evaluating the Influence of Sex on Birth Weight and Preweaning Gain in Beef Cattle

Abstract

Data on the birth weights and daily gains from birth to weaning of 1434 bulls and 1512 heifers were studied to evaluate the influence of sex on these traits. The mean differences, ratios of the means, and the variation within each sex were evaluated to determine whether an additive or a multiplicative type of adjustment was more nearly appropriate for each trait. Bull calves averaged 5.2 lb. or 1.076 times heavier than heifers at birth. The data were not conclusive in determining which type of factor was more appropriate. The difference in results from using one type or another is considered too small to be of practical significance. The daily gain of bull calves from birth to weaning was 0.113 lb. or 1.073 times greater than that of heifers. A multiplicative factor based on the ratio of the mean daily gains was considered more appropriate for the combined data from all of the herds studied. The average daily gain and the average difference between bulls and heifers differed significantly between herds studied. Although a clear cut explanation for the differences between herds was not evident it was postulated that the average magnitude of the gains as well as the shape of the growth curve induced by environmental conditions may have been significant factors. Copyright © . .