Sources of Variation in the Birth Weight of Holstein-Friesian Calves

Abstract

Data on Holstein-Friesian calves in three unrelated herds were analyzed to determine some of the causes of variation in birth weight and to compare the birth weight of inbred and outbred offspring by the same sire. The mean birth weights of 794 calves were 92.9 lbs. and 85.5 lbs. for the outbreds and inbreds, respectively. Male calves averaged 5.2 lbs. heavier than females and calves from “first calf” heifers were approximately 10 lbs. lighter than were calves from dams of later calving sequence. Herd differences accounted for about 22 per cent, sex for 7 per cent, and calving sequence for 14 per cent of the total variation in birth weight. Season and year had little or no effect on birth weight. Approximately 60 per cent of the remaining variation in birth weight was due to the genotype of the calf. Birth weight declined an average of 0.28 lb. for each increase of one per cent inbreeding, with size of dam constant. The inbreeding effect varied significantly from sire to sire, apparently due to differences in the average birth weight transmitted by different sires. The inbred calves of sires transmitting heavy birth weights tended to be heavier than the outbred calves because of having more of their sires’ genes, which cancels, at least in part, the reduction in birth weight from increased homozygosity. © 1947, American Dairy Science Association. All rights reserved.