ADDITIVE AGE OF DAM ADJUSTMENT FACTORS FOR WEANING WEIGHT OF BEEF CATTLE

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Abstract
A study of 373 351 weaning weight records from the National and the Alberta Provincial Record of Performance programs for beef cattle, representing 279 061 cows from 5421 herds during the period 1971 through 1977, was used to examine age of dam by breed of sire interactions and to derive a set of additive age of dam adjustment factors for calf weaning weight. The model included fixed effects due to age of dam–sex of calf–breed of dam subclasses, breed of sire, age of dam–breed of sire interactions and year of calving plus random effects due to herds and cows within herds. A relatively small age of dam–breed of sire interaction mean square indicated that one set of adjustment factors could be used for calves from all the breeds of sire, even though the interaction term was statistically significant (P < 0.005). A set of additive factors to adjust calf weaning weight for age of dam within sex of calf and breed of dam are presented for the following breeds and breed crosses of dam: Angus, Charolais, Hereford, Shorthorn, British breed crosses, half Charolais–half British, half Simmental–half British and "others."

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