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Heterosis from Crosses among British Breeds of Beef Cattle: Post-Weaning Performance to Slaughter^{1, 2, 3,}

Virginia Polytechnic Institute, Blacksburg

Abstract

Data from 471 straightbred, two-breed, three-breed and backcross steers and heifers were used to estimate heterosis in gain and grade from weaning to time of slaughter. Steer and heifer data were analyzed separately, since postweaning management was different for the two sexes. Age of dam effects were not considered in the analyses, since all cows were the same age in a given year. The effects of mating type, year of birth (confounded with age of dam and parity) and age on weight were estimated through least squares analyses and the data adjusted accordingly.

Least squares means, as well as mid-parent values and deviations of the crossbred least squares means from the appropriate mid-parent value, were calculated for each of the postweaning traits studied. Comparisons of practical interest were also made between means computed for each of the four major systems of mating (i.e., straightbred, twobreed, three-breed and backcrosses). Twobreed cross heifers were significantly superior to their purebred contemporaries in feedlot ADG, slaughter weight and slaughter grade. No significant differences were found among the crossbred heifer groups in feedlot ADG, slaughter weight or slaughter grade. Among the steer groups, two-breed crosses were significantly superior to both purebred and backcross contemporaries in yearling ADG, yearling weight and slaughter weight, and significantly superior in all comparisons in slaughter grade. Essentially no differences were found among the four groups in feedlot ADG.

In general, results indicate that some heterosis in postweaning growth rate and weight (2.1% to 5.2%) can be expected up to about 18 mo. of age. A significant advantage of crossbreds over straightbreds in weight after approximately 18 mo. of age resulted from the maintenance of a significant advantage at younger ages. Differences in slaughter grades were generally small, with the significant deviations (in favor of the crossbreds) interpreted as a reflection of the heavier slaughter weights and presumed higher condition of the crossbreds rather than heterosis in slaughter grade per se.

¹ Published with the approval of the Director, Agriculture and Life Sciences.

² Research conducted in cooperation with the Animal Husbandry Research Division, A.R.S., U.S.D.A., and State experiment stations in the Southern Region of the United States as part of Regional Project S-10, "The Improvement of Beef Cattle Through Breeding Methods".

³ Appreciation is expressed to Dr. E. J. Warwick Chief, Beef Cattle Research Branch, An. Hus. Res. Div., A.R.S., U.S.D.A., who assisted in planning the experiment.

⁴ Deceased. Formerly Chief, Swine Research Division, A.R.S., U.S.D.A., Beltsville, Maryland. Prior to that, Professor of Animal Husbandry, Virginia Polytechnic Institute.