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

Author
item SANDERS, J. - TEXAS A&M UNIVERSITY
item KEY, K. - TEXAS A&M UNIVERSITY
item Riley, David
item LUNT, D. - TEXAS AGRIC.EXP. STATION

Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Proceedings
Publication Acceptance Date: 2/8/2005
Publication Date: 2/8/2005
Citation: 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. American Society of Animal Science Southern Section Meeting. Symposium on Tropically Adapted Breeds. Regional Project S-1013. Little Rock, AR., February 8, 2005. pp.196-203.

Interpretive Summary: The amount of crossbred superiority (heterosis or hybrid vigor) for cow reproduction and maternal traits is being evaluated in herds of Brahman, Angus, Nellore, Hereford, and various crosses involving these breeds. According to crossbreeding theory, second cross (F2) animals should express ½ the hybrid vigor expressed by first cross (F1) animals. Average calf crop born for Brahman, Angus, and Hereford cows was .68, .93, and .80, respectively. Brahman/Angus and Brahman/Hereford F1 averages were .90 and .89, giving heterosis estimates of .095 and .15. Brahman/Angus and Brahman/Hereford F2 averages were .74 and .87, giving heterosis estimates in the F2 of -.065 and .13. Average calf crop weaned for Brahman, Angus, and Hereford cows were .59, .83, and .72, respectively. Brahman/Angus and Brahman/Hereford F1 averages were .82 and .82, giving heterosis estimates of .11 and .16. Brahman/Angus and Brahman/Hereford F2 averages were .64 and .81, giving heterosis estimates in the F2 of -.06 and +.15, respectively. Survival rates in Brahman and Hereford calves were .79 +/- .03 and .91 +/- .03. Survival rates in Hereford sired calves out of Brahman cows and Brahman sired calves out of Hereford cows were .95 and .98, giving a heterosis estimate of .115 for direct effects on calf survival. Calf survival in Brahman/Hereford F2 calves was .98. Weaning weights in Brahman and Hereford calves were 460.6 and 386.3 lb. Weaning weights in Hereford sired calves out of Brahman cows and Brahman sired calves out of Hereford cows were 494.6 and 449.2, respectively, giving a heterosis estimate of 48.5 lb for direct effects on weaning weight. Weaning weight in Brahman/Hereford F2 calves was 480.0, giving an estimate of 56.6 lb for the combination of maternal heterosis plus retained heterosis for direct effects on weaning weight. Average cow weights at 4 yr of age for Brahman, Angus, and Hereford cows were 1111, 1142, and 1054 lb,. Brahman/Angus and Brahman/Hereford F1 averages were 1177 and 1153 lb, giving heterosis estimates of 50 and 76 lb. Brahman/Angus and Brahman/Hereford F2 averages were 1087 and 1175 lb, giving heterosis estimates in the F2 of –40 and +92 lb. These preliminary results indicate that for a variety of cow traits, Brahman-Hereford F2 performed substantially above what would be expected from crossbreeding theory, but Brahman-Angus F2 crosses performed much lower that what would be expected.

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. Average calf crop born for Brahman, Angus, and Hereford cows has been 0.68 ± 0.03, 0.93 ± 0.03, and 0.80 ± 0.03, respectively. Brahman/Angus and Brahman/Hereford F1 averages have been 0.90 ± 0.03 and 0.89 ± 0.02, giving heterosis estimates of 0.095 and 0.15. Brahman/Angus and Brahman/Hereford F2 averages have been 0.74 ± 0.03 and 0.87 ± 0.03, giving heterosis estimates in the F2 of -0.065 and +0.13. Average calf crop weaned for Brahman, Angus, and Hereford cows has been 0.59 ± 0.03, 0.83 ± 0.04, and 0.72 ± 0.04, respectively. Brahman/Angus and Brahman/Hereford F1 averages have been 0.82 ± 0.03 and 0.82 ± 0.02, giving heterosis estimates of 0.11 and 0.155. Brahman/Angus and Brahman/ Hereford F2 averages have been 0.64 ± 0.04 and 0.81 ± 0.04, giving heterosis estimates in the F2 of -0.060 and +0.145. Reciprocal Brahman/Hereford F1 calves were produced, allowing estimates of heterosis for calf survival and weaning weight. Survival rates in straightbred Brahman and Hereford calves were 0.79 ± 0.03 and 0.91 ± 0.03. Survival rates in Hereford sired calves out of Brahman cows and Brahman sired calves out of Hereford cows were 0.95 ± 0.03 and 0.98 ± 0.09, respectively, giving a heterosis estimate of 0.115 for direct effects on calf survival. Calf survival in Brahman/Hereford F2 calves (reciprocals combined) was 0.98 ± 0.09. This gives an estimate of .13 for the combination of maternal heterosis plus retained heterosis for direct effects on calf survival. Weaning weights in straightbred Brahman and Hereford calves were 460.6 ± 9.9 and 386.3 ± 10.8 lb. Weaning weights in Hereford sired calves out of Brahman cows and Brahman sired calves out of Hereford cows were 494.6 ± 10.6 and 449.2 ± 21.6, respectively, giving a heterosis estimate of 48.5 lb for direct effects on weaning weight. Weaning weight in Brahman/ Hereford F2 calves (reciprocals combined) was 480.0 ± 7.9, giving an estimate of 56.6 lb for the combination of maternal heterosis plus retained heterosis for direct effects on weaning weight. Average cow weight at four years of age for Brahman, Angus, and Hereford cows was 1,111 ± 22, 1,142 ± 31, and 1,054 ± 24 lb, respectively. Brahman/Angus and Brahman/Hereford F1 averages were 1,177 ± 24 and 1,153 ± 37 lb, giving heterosis estimates of 50 and 76 lb. Brahman/Angus and Brahman/Hereford F2 averages were 1,087 ± 31 and 1,175 ± 31 lb, giving heterosis estimates in the F2 of –40 ± 31 and +92 ± 31 lb.