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Comparison of Two- and Three-Way Rotational Crossing and Synthetic Variety Production Involving Inbred Lines of Hereford Cattle: Postweaning Traits¹

US Department of Agriculture and Montana Agricultural Experiment Station, Miles City 59301, Cooperating

Abstract

Data for this linecrossing study were the postweaning growth and weight records of calves born from 1967 through 1975. The records consisted of 264 bull (M) and 263 heifer (F) straightline (SL) calves; 108 M and 100 F two-line rotational cross (2W) calves; 130 M and 102 F three-line rotational cross (3W) calves and 58 M and 51 F synthetic variety (SV) calves, all in the Hereford breed. Average inbreeding percentages of calves and dams in Lines 1, 4, 6 and 10 were 24, 28, 34 and 28, respectively. The M calves were fed a growing-fattening diet for 196 d after a 14-d period of adjustment to postweaning environment. The F calves were fed to gain approximately .5 kg daily during winter from weaning to about 12 mo of age and were then grazed on native pasture until about 18 mo of age. For M, average percentage increases over SL by 2W, 3W and SV combined over three generations were, respectively, 9.0, 11.0, 11.6 for initial weight; 5.9, 8.1, 8.8 for 140-d weight; 4.8, 7.2, 7.7 for final 196-d weight and 1.5, 4.2, 4.7 for 196-d gain. All above estimates of increased weight or gain over SL were significant except for 196-d gain in 2W. For F, average percentage increases over SL by 2W, 3W and SV, respectively, were 9.0, 10.9, 11.3 for initial weight; 8.2, 9.2, 8.4 for 12-mo weight; 7.5, 7.7, 9.1 for 18-mo weight-, 5.2, 5.3, 5.7 for 18-mo score. All these estimated increases over SL were significant. The difference between heterosis levels of 2W and 3W for each above growth trait within sex was nonsignificant, although heterosis values for 3W were consistently the larger. The M and F animals of SV exhibited essentially the same heterosis levels as those in 3W.

¹ This study was conducted at the Livestock and Range Research Station, Miles City, MT, in cooperation with the Montana Agr. Exp. Sta., Bozeman. Publication has been approved by the Director of the Montana Agr. Exp. Sta., as Journal Series No. 1325.

² Livestock and Range Research Sta., Western Region, ARS, USDA, Miles City, MT 59301.

³ Present address: Biometrical Services, ARS, USDA, Fort Collins, CO 80521.

⁴ Montana Agr. Exp. Sta., Bozeman 59717.

⁵ Authors express appreciation to Dr. J. S. Brinks of the Colorado Agr. Exp. Sta. for his contribution to the planning of the experiment, and to Mr. W. C. Russell, Graduate Research Assistant, Colorado State Univ. for assistance with data processing.