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Individual Heterosis for Postweaning Growth Efficiency in Beef Cattle¹

U.S. Department of Agriculture and University of Nebraska, Clay Center 68933

Abstract

Effects of heterosis on efficiency of post-weaning growth were evaluated for weight-constant and time-constant intervals in phase 1 of a comprehensive heterosis experiment by a comparison of reciprocal crossbred and straightbred Hereford, Angus and Shorthorn steers. Heterosis in feed utilization can be evaluated more accurately in weight-constant intervals because the confounding of heterosis in growth rate with the increased maintenance from heavier initial and final weights, that occurs in time-constant feeding periods, can be avoided.

Total digestibile nutrient conversions (TDN/GAIN) were evaluated for eight 22.7-kg intervals from 226.8 to 408.2 kg and for the total period for 142 crossbred and 144 straightbred, individually-fed steers born in 1961, 1962 and 1963 by a fitting of the quadratic regression of cumulative TDN on age change in weight. TDN consumption, postweaning weights and efficiency by 28-day periods and average daily gain for the 224-day test were evaluated by a fitting of linear and quadratic regressions of cumulative TDN and weight, respectively, on days fed.

From 227 to 408 kg live weight, TDN/GAIN was 1.6% less for crossbred than for straight-bred steers in the direction expected because crossbred steers gained 2.8% faster and thus required fewer days on feed and less feed on maintenance during the weight interval than straightbreds required.

In the time-constant 224-day test, crossbred steers were significantly (2.6%) heavier than straightbred steers at the start, averaged 2.9% heavier throughout the 224-day test and consumed significantly (2.4%) more total TDN because of greater weight maintained. Crossbred advantage in growth and feed conversion was greater in the earlier than in the later postweaning periods. However, crossbreds were slightly more efficient than straightbreds during the 224-day time-constant test (.8% less TDN/GAIN) because of the 2.8% advantage in postweaning growth rate.

¹ Published as Paper 5377, Journal Series, Nebraska Agricultural Experiment Station, Lincoln. Contribution from North Central Regional Project NC-1, Improvement of Beef Cattle through Breeding Methods. Partial publication of senior author's dissertation research.

² Present address: Department of Meat and Animal Science, University of Wisconsin, Madison 53706.

³ U.S. Meat Animal Research Center, North Central Region, Agricultural Research Service, USDA, Clay Center, NE 68933.

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