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Heterosis Retained in Advanced Generations of Crosses among Angus and Hereford Cattle¹

University of Nebraska, Lincoln 68583 and US Department of Agriculture, Clay Center, NE 68933

Abstract

Data from 1, 909 purebred, F₁, backcross and F₂ and F₃ inter se combinations of Angus and Hereford were used to estimate average individual, maternal and grandmaternal genetic effects, individual and maternal heterosis, dominance and epistatic genetic effects. Models for evaluating heterosis and epistatic or recombination effects were discussed. Average individual effects indicate that Angus, compared with Hereford, had calves that were born earlier, had lighter birth weights, lower pre- and postweaning gains and lower pregnancy rates. Angus also produced lighter weight carcasses with more fat cover and marbling. Maternal effects of Angus were in the direction of reduced birth weight, greater calving ease, higher preweaning but lower postweaning growth rate and increased fatness when contrasted with Hereford. There was a tendency for opposite direction of maternal and grandmaternal effects for traits influenced by preweaning maternal environment. When additive x additive effects were ignored, total heterosis was significant for earlier day born, heavier birth weight, preweaning and postweaning gain, and heavier and fatter carcasses. Heterosis retained in F₃ inter se vs F₁ generation crosses indicated that net epistatic effects were relatively negligible for date of calving, birth weight, weaning gain and fat cover. There was a greater reduction of heterosis effects than expected from dominance alone for survival, pregnancy and marbling score. Loss of heterosis in F₃ was less than expected for postweaning gain, carcass weight and rib eye area. Except for survival, pregnancy and marbling, these deviations from dominance expectations, or lack of them, are favorable for F₃ composite populations.

¹ Published as Paper No. 7534 Journal Ser., Nebraska Agr. Exp. Sta., Lincoln. A contribution from North Central Regional Project NC-1.

² Anim. Sci. Dept., Univ. of Nebraska, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center 68933.

³ Roman L. Hruska U.S. Meat Animal Research Center, ARS, USDA, Clay Center, NE.

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