Factors Affecting the Growth of Beef Calves during the Suckling Period

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Abstract
A study has been made of the relation between the calf's rate of growth from birth to four months of age (designated as G) and its 240 day weaning weight (designated as W). The data analyzed were eight monthly weights of each of 159 purebred Hereford bull and heifer calves out of 57 cows in the University of California herd at Davis. Correction factors were estimated for the effects of sex, age of dam, and year and season of birth on G and W. A second degree regression curve describes adequately the effect of age of dam on both G and W. Dams in the age range seven to ten years produced the calves that grew fastest to four months of age and were heaviest at weaning (240 days). However, from four months to eight months of age the calves from first calf heifers and to a lesser extent from second calf cows grew faster than those from cows in the optimum age range. This is probably due to a greater persistency in lactation of young cows as compared to older cows since several investigators have found this to be the case in dairy cattle. Heifer calves weighed 68 pounds less than bull calves at weaning. Differences between cows accounted for 34 percent and 48 percent of the variances of G and W respectively. The following correlations between G and W were found: rGW (within dams) =.62; rGW (between dams) =.91; rGW (between dams based on a single record) =.73. In the light of the above estimates and the analysis of the effect of the age of dam on lactation it is concluded that the lactating ability of a cow makes a major contribution to the growth of the calf throughout the entire suckling period. The results of a selection experiment are reported in which cows were considered culled on the basis of the G values of first calves. The results indicated that this criterion could be used to predict a cow's future production sufficiently well to warrant its use as part of a system for selecting replacement cows in the case of those cattlemen that veal a heifer's first calf at four months of age. Copyright © . .

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