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Title: EVALUATION OF HETEROSIS RETENTION FOR COW PRODUCTIVITY TRAITS IN BOS INDICUS-BOS TAURUS CROSSES.

Author
item WRIGHT, B.
item SANDERS, J.
item KEY, K.
item Riley, David
item LUNT, D.

Submitted to: Beef Cattle Research in Texas
Publication Type: Experiment Station
Publication Acceptance Date: 12/7/2005
Publication Date: 12/7/2005
Citation: Wright, B.A., Sanders, J.O., Key, K.L., Riley, D.G., Lunt, D.K. 2005. Evaluation of heterosis retention for cow productivity traits in bos indicus-bos taurus crosses. In: Beef Cattle Research in Texas. pp. 11-15. 2005. Depart. Anim. Sci., Texas A&M Univ., College Station.

Interpretive Summary: Crossbreeding theory predicts that the performance of cattle from the first cross (F1) of two breeds will be greater than the average performance (for a wide variety of traits) of the purebreds that comprise the F1. However, this superiority, or hybrid vigor, is expected to be halved in the performance of the second cross (F2, which results from mating F1 parents). For traits that hybrid vigor strongly influences, such as cow reproductive traits, this is a tremendous loss in performance. A study is in progress to evaluate calf crop born, calf crop weaned, and pregnancy rate in cows and birth weight, weaning weight, and survival of their calves. In crosses of Brahman and Angus, the F1 exceeded the parental breed averages for all traits analyzed. The F2 Brahman/Angus group mean was lower for calf crop born, calf crop weaned, and calf survival than the purebred average and represents a total loss of hybrid vigor. In crosses of Brahman and Hereford, both the F1 and F2 crosses exceeded the purebred averages for all traits analyzed, and the F2 group means for reproductive traits were equal to or greater than F1 means. This indicates that all of the hybrid vigor was expressed by the F2 Brahman-Hereford. Both of these (total loss of hybrid vigor in F2 Brahman-Angus and total retention of hybrid vigor in F2 Brahman-Hereford) are quite different than what is predicted by crossbreeding theory, and additional data will be collected to verify these preliminary results.

Technical Abstract: Heterosis and heterosis retention for cow reproduction and maternal traits are being evaluated in herds of Brahman, Angus, Nellore, Hereford and various crosses involving these breeds. Traits analyzed were calf crop born, calf crop weaned, and pregnancy rate in the cows and birth weight, weaning weight, and survival of their calves. The F1 Brahman/Angus, as well as the F1 and F2 Brahman/Hereford exceeded the parental breed averages for all traits analyzed. The F2 Brahman/Angus group mean was lower in calf crop born, calf crop weaned, and calf survival than the parental breed average. The estimates for heterosis retention exceeded predictions of the dominance model in Brahman/Hereford crosses, but were below dominance model predictions in Brahman/Angus crosses.