Evidence of a negative relationship between heifer growth and first calf weaning weight in commercial beef herds

Abstract

The relationship between weaning weights of beef heifers and their first calves, after adjustment for age and sex/age differences respectively, was examined in 1626 heifers from eight herds in the South-east of South Australia and the Western District of Victoria. Data were obtained from 64 herd years and included only heifers that had weaned a calf after calving at two (seven herds) or three (one herd) years of age. Within years in each herd the relationship (P<0.05) was negative (slope= -0.068 kg/kg, SE = 0.0267) but accounted for only 0.4% of the variation in weaning weight of progeny. This confirms previous findings that within any heifer drop, weaning weight is a poor predictor of subsequent calf-rearing ability. The relationship between herd year means (P<0.01) was negative (slope = -0.50 kg/kg, SE = 0.15) and accounted for 15% of the variation in weaning weights of progeny. Over the range in heifer mean weaning weight from 170 to 250 kg, mean progeny weaning weights tended to decrease 5 kg for every 10 kg increase in their dams' average weaning weight. However, there was evidence that the negative relationship was curvilinear (P< 0.05) such that effects on weaning weights of progeny diminished markedly when weaning weights of heifers exceeded approximately 200 kg. The possible involvement of nutritional environment, both during the year of heifer development before weaning and in the expression of milk production in terms of calf weaning weight several years later, is discussed in relation to the expression of the phenotypic relationship in different years and locations.