Maternal heterosis was estimated from Hereford, 25% Simmental -75% Hereford, 50% Simmental - 50% Hereford and 75% Simmental - 25% Hereford dams. Sample halves of these dam breed groups were bred to Charolais and Tarentaise sires to produce calves at 3 to 8 yr of age. Cows were managed consistent with practices for western range environments. Maternal heterosis was estimated by regression techniques for 22 traits. Maternal heterosis was not significant for day of conception, number of services, gestation length or calving difficulty. Estimates of maternal heterosis for calf growth traits ranged from .7% for weaning height to 5.2% for weaning weight and 7.5% for weaning condition score. Calf weight per unit of cow weight at weaning showed significant maternal heterosis (7.1%). Higher levels of maternal heterosis were exhibited for milk production (18.0 to 24.4%), proportion of dams that calved and that weaned calves (11.5 and 10.4%) and calf weaning weight per cow exposed to breeding (17.9%). There was a decrease in percentage maternal heterosis for most traits as dam age increased.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XV. Beef cattle, sheep and pig genetics and breeding, fibre, fur and meat quality., , 279–282, 1990
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