Lifetime productivity of purebred and crossbred cows of Angus and milking shorthorn parentage: weights and scores.

Lifetime productivity of 242 purebred and reciprocal crossbred Angus (A) and Milking Shorthorn (M) cows was studied. Cows were born in the fall during the 5-yr period from 1966 through 1970. Data from each parity, one through six, were analyzed separately by the method of least-squares. The basic statistical model included effects of breed of cow and year of cow birth plus the first-order interaction. Calf weight data were adjusted for effects of sex and calf age. Production stage was included for analyses of cow weights and condition scores. Data from parities seven through 13 were combined in one analysis with the effect of parity added to the model. Appropriate contrasts of estimates of breed means provided estimates of additive, heterotic, maternal and grandmaternal effects. Using pooled averages, crossbred cows were 22.5 kg (5.7%, P less than .01) heavier and .15 condition score units (5.3%, P less than .01) fatter than purebred cows. Condition scores of AM, MA and AA cows were higher (P less than .05) than those of MM cows. Calves from crossbred cows averaged 6.1 and 9.8 kg heavier (4.2 and 4.7%, P less than .01) at 120 and 210 d of age, respectively, than calves from purebred cows. Calves from AM, MA and MM dams were heavier (P less than .05) than those from AA dams. Calf weight at 210 d of age as a percentage of cow weight was used as a measure of efficiency of production. The heterosis contrast was 3.6% (P less than .01), which represented an 8.5% increase of the crossbreds relative to the mean of purebred cows (42.4%).