Heterosis Effects on Growth Rate and Feed Efficiency of Beef Steers

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Abstract
The Hereford, Angus and Shorthorn breeds and all reciprocal crosses among them were included in an experiment designed to evaluate heterosis effects in crosses among these breeds. Data were collected on four crops of steers (1960, 1961, 1962 and 1963) for a 252-day postweaning feeding period on a growing-fattening ration of approximately 65% TDN. Each year the postweaning feeding period started at weaning at an average age of approximately 200 days. The first crop (1960) was group-fed and the last three crops (1961, 1962 and 1963) were individually self-fed. Data were obtained on 374 steers for the 4 years and on 286 for the last 3 years. The analysis included an evaluation of heterosis and related effects on 200-day weight, subsequent age-constant weights, average daily gain by periods, measures of feed efficiency by periods and slaughter grade. The 252-day postweaning feeding period was divided into three 84-day periods to evaluate heterosis effects on growth rate and feed efficiency by periods. The heterosis effect on growth rate decreased with increasing age in the three 84-day periods. Thus, the heterosis effect on growth rate was related to age. The heterosis effects on growth rate were not significant during the third 84-day period. The heterosis effects on different measures of feed efficiency were small and were generally not significant. Interactions of years with breed of sire and breed of dam were relatively unimportant. The heterosis effects attributable to sires within a breed were not generally important. Thus, the heterosis observed was a characteristic of breeds used rather than of specific sires within breeds. Heterosis effects were larger in the Hereford-Angus and the Hereford-Shorthorn crosses than in the Angus-Shorthorn cross. Heterosis effects on growth rate and different measures of feed efficiency were not important for the Angus-Shorthorn cross. Thus, the Hereford breed contributed more than either the Angus or Shorthorn breed to the average heterosis effects. Breed effects existed for many of the traits studied. The Herefords were superior in growth rate and feed efficiency. The Shorthorns were superior to the Angus in measures of growth rate and feed efficiency. However, because of the increased fatness of the Shorthorn carcass (Gregory et al., 1966b) and the slight advantage for Angus in weaning weight, the Angus were superior to the Shorthorn in amount of retail product per unit of TDN consumed from weaning to slaughter. Copyright © 1966. American Society of Animal Science . Copyright 1966 by American Society of Animal Science

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