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Title: GENOTYPE X ENVIRONMENT INTERACTIONS IN BRAHMAN, ANGUS, AND RECIPROCAL-CROSS COWS AND THEIR CALVES

Author
item Brown, Michael
item BROWN, JR. A - UNIVERSITY OF ARKANSAS
item SANDELIN, BROC - UNIVERSITY OF ARKANSAS

Submitted to: Miscellaneous Publishing Information Bulletin
Publication Type: Other
Publication Acceptance Date: 2/5/2006
Publication Date: 4/1/2006
Citation: Brown, M.A., Brown, J.H., Sandelin, B. 2006. Genotype x environment interactions in Brahman, Angus, and reciprocal-cross cows and their calves. In: A Compilation of Research Results Involving Tropically Adapted Beef Cattle Breeds. Southern Section of American Society of Animal Science Meeting, February 8, 2005, Little Rock, Arkansas. Southern Series Cooperative Bulletin 405. p. 166-181.

Interpretive Summary: Crossbreeding systems in beef cattle are designed to result in genetic improvement in economically important traits through the expression of heterosis, maternal breed effects, and direct breed effects. It is important to know whether these genetic effects vary across production environments and the nature of this variation, if it exists. Endophyte-infected tall fescue has been shown to dramatically reduce calf growth and milk production and reproduction in beef cows grazing this forage. Research evaluating Brahman, Angus, and reciprocal-cross calves grazing common bermudagrass or endophyte-infected tall fescue demonstrated that direct breed effects for preweaning traits were larger on common bermudagrass compared to tall fescue, suggesting that the best choices of breeds in crossbreeding systems may depend on the production environment for optimal performance. Results from this research also demonstrated that the use of Brahman x Angus or Angus x Brahman crossbred cows bred to a bull of a third breed could be a beneficial management tool for producers faced with the management of endophyte-infected tall fescue due to the apparent tolerance of the Brahman-cross cows and their calves to endophyte-infected tall fescue. Rotating cows and calves from endophyte-infected tall fescue to bermudagrass in the summer moderated some of the effects of endophyte-infected tall fescue on calf growth but performance was not always comparable to bermudagrass. The rotation did appear to be more beneficial for purebred cows than crossbred cows, considering reproductive traits. Although the use of crosses of Brahman and Angus and/or rotation from endophyte-infected tall fescue to common bermudagrass does not eliminate production losses attributable to endophyte-infected tall fescue, it appeared to reduce these losses substantially. Consequently, use of the technology developed in this research may be beneficial in developing efficient cow-calf systems where endophyte-infected tall fescue pastures are prevalent.

Technical Abstract: Stability of direct and maternal breed effects and individual and maternal heterosis across forage type was evaluated in a diallel of Brahman and Angus using preweaning data from 486 purebred and reciprocal-cross calves, milk yield and quality data from 139 purebred and reciprocal-cross cows, and reproductive and preweaning data on 190 purebred and reciprocal cross cows and their 434 Hereford-sired calves. Cows and calves were managed on either common bermudagrass or endophyte-infected tall fescue from 1985 through 1994; a combination of the two forages was included from 1995 through 1997. Calves were spring-born and not creep-fed. Milk yield was estimated by machine milking and milk quality was evaluated in a commercial laboratory. Direct heterosis for birth weight, 205-d weight, weaning hip height, and weaning weight:height ratio (WT/HT) was important (P < 0.01) and consistent across forage type. Maternal effects for weaning hip height favored Angus on bermudagrass (P < 0.05) but not tall fescue. Direct effects for weaning hip height were larger in calves on bermudagrass than tall fescue. Direct heterosis for milk yield was evident on bermudagrass, tall fescue, and a combination of the forages (P < 0.01). Direct breed effects for milk fat were similar across forages in favor of Brahman (P < 0.01). Direct heterosis for calving rate was larger on tall fescue than bermudagrass or the forage combination (P < 0.05), whereas maternal effects were larger on bermudagrass than on the forage combination (P < 0.10). Maternal heterosis for birth weight was negative on bermudagrass (P < 0.11) but positive on tall fescue and the forage combination (P < 0.10). Maternal heterosis for 205-d weight, calf weaning hip height, and calf weaning weight:height ratio was generally greater on tall fescue than bermudagrass (P < 0.10). Heterosis for weaning weight per cow exposed was substantial on all forages (P < 0.01) and was greater on tall fescue (P < 0.01) than bermudagrass or the forage combination These data indicate direct heterosis for preweaning traits was relatively stable across the two forage types but maternal and direct breed effects may vary with forage type. These data also evidenced more advantage to Brahman-cross cows over purebreds on tall fescue than bermudagrass.