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Title: SEASONAL WEIGHT CHANGES AND PREPARTUM WEIGHT:HEIGHT RATIO IN ANGUS AND BRAHMAN COWS GRAZING COMMON BERMUDAGRASS OR ENDOPHYTE-INFECTED TALL FESCUE

Author
item BROWN, MICHAEL - 6218-05-10
item BROWN, A - U. OF ARKANSAS, FAY.
item SANDELIN, BROC - U. OF ARKANSAS, FAY.

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2003
Publication Date: 10/1/2003
Citation: Brown, M.A., Brown, A.H., Sandelin, B. 2003. Seasonal weight changes and prepartum weight:height ratio in angus and brahman cows grazing common bermudagrass or endophyte-infected tall fescue. Professional Animal Scientist. 19:342-349.

Interpretive Summary: Nutrition derived from forages by beef cows plays a major role in the efficiency of cow-calf production. In heifers, winter and spring gains prior to the first breeding season are associated with reproductive performance. Winter gain in beef cows directly influences body condition at calving, which has a well-documented impact on rebreeding. Postcalving weight changes can have an additional affect on subsequent rebreeding performance in conjunction with body condition at calving. However, there is little information on the impact of breed and forage type on seasonal weight gains and prepartum body condition in reproductive beef females. Research by USDA-ARS and University of Arkansas scientists evaluated the effects of breed, forage environment, and production status on seasonal weight changes and prepartum body condition in Angus and Brahman heifers and cows grazing common bermudagrass or endophyte-infected tall fescue. Research indicated that higher winter gains did not improve reproductive performance and higher spring gains were beneficial only in Angus cows that calved during the spring. Similar to winter gain, precalving body condition was not a useful indicator of later reproduction. However, higher summer gains in heifers and cows that had calved in the spring, was a useful indicator of rebreeding in the summer breeding season. While these results indicate that the best indicator of future reproduction was gain during the breeding season, winter and spring gains, as well as precalving body condition may be important in heifers and cows that have lower body conditions than the animals in this study.

Technical Abstract: Cow weights, hip heights, and reproductive data taken from 1986 to 1992 on 80 Angus and 80 Brahman cows grazing common bermudagrass or tall fescue were used to evaluate the effects of breed, forage environment, and production status on seasonal weight changes and precalving body condition. Each year, females were bred during 75-d breeding seasons starting in late May or early June. Cows were weighed at weaning, precalving, and postcalving each year and gains were computed for winter, spring , and summer periods prior to the calving season the next year. Weight:height ratios (kg/cm) were computed from hip height data taken in February of each year of the study to estimate body condition prior to calving and breeding. Thus, gain and condition data corresponded to seasons prior to the subsequent calf crop. Cows in each breed-forage subclass were classified into four groups based on all possible combinations of prior and subsequent year calving data. Winter gains were not associated with whether a heifer or cow became pregnant in the subsequent breeding season. There was a breed x forage interaction for winter ADG in cows (P<0.01) with the advantage of tall fescue over bermudagrass in Angus cows (P<0.01) larger than the same advantage in Brahman cows (P<0.01). Spring gains in open heifers or cows did not influence subsequent reproduction, but Angus cows that calved in the spring and rebred had more favorable spring weight changes compared to contemporaries that calved in the spring but did not rebreed. There was a breed x forage interaction for spring ADG in both heifers and cows (P<0.10); Brahman and Angus had similar ADG on tall fescue but Brahman had higher ADG on bermudagrass than Angus (P<0.01). Precalving weight:height ratios were not useful indicators of subsequent reproduction. Increased summer ADG during the breeding season was a useful indicator of subsequent calving rates in heifers and in cows that had calved the previous spring, but not in cows that were open the previous spring. There was evidence of a breed x forage interaction for summer ADG in both heifers and cows (P<0.01); Brahman and Angus had similar ADG on bermudagrass but Brahman had higher ADG on tall fescue than Angus (P<0.01). Consequently, these data indicate the best predictor of subsequent reproduction in spring-calving cows is summer weight change and these results provide further evidence of the tolerance of Brahman to endophyte-infected tall fescue in the summer.