Abstract
Effects of maternal heterosis were evaluated for postweaning growth and carcass traits of 497 crossbred steers and 356 crossbred heifers produced from 1963 through 1968 in phase 2 of a comprehensive heterosis experiment. Maternal heterosis was estimated by a comparison of two-breed cross progeny from straightbred Hereford, Angus and Shorthorn cows to three-breed cross progeny from F1 crossbred cows. Postweaning weights and average daily gains for the three 84-day periods and for the entire 252-day feeding test were evaluated. Carcass traits were evaluated at both age- and weight-constant endpoints. Steers and heifers from crossbred dams were 10.4 kg (5.3%, P<1) and 7.9 kg (4.2%, P<.001) heavier than progeny from straightbred dams at 200 days of age but were only 5.9 kg (1.4%) and 4.9 kg (1.2%) heavier at 452 days of age, because of compensatory effects of maternal heterosis on postweaning average daily gain (−.02 and −.01 kg). Maternal heterosis effects were unfavorable and largest on first-period growth rate of heifers but on last-period growth rate of steers. The unfavorable maternal heterosis for growth rate was associated with slightly fatter carcass composition of progeny from crossbred dams, apparently from greater milk production of crossbred cows. Maternal heterosis effects on carcass traits of steers and heifers at either a constant age or constant.
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