ARS | Publication request: Post Weaning Performance of Spring-Born Calves Weaned from Tall Fescue Pastures with a Wild-Type Endophyte or a Non-Toxic Novel Endophyte

Submitted to: Arkansas Agricultural Experiment Station Research Series
Publication Type: Experiment Station
Publication Acceptance Date: August 15, 2008
Publication Date: N/A

Technical Abstract: Numerous studies have reported compensatory gain by yearling cattle that grazed toxic endophyte-infected `KY-31¿ tall fescue (E+), but few studies have reported post-weaning performance by calves weaned from E+. Our objective was to compare post-weaning performance by spring-born calves grazing E+ with that of calves grazing a non-toxic endophyte-tall fescue association developed at the Univ. of Arkansas (NE+). Gelbvieh × Angus crossbred cows (n=134; 1,078 lb initial BW) were allocated to one of four 25-acre pastures in 2005 and to one of eight 25-acre pastures in 2006. Cows began grazing during the fall of each year. Calves were born and remained on their assigned pastures until weaning in 2006, but were removed from NE+ in the summer of 2005 because of low forage availability. After weaning, calves grazed bermudagrass pastures followed by winter annuals. Steers weaned from NE+ were heavier (P < 0.01) at weaning and throughout the post-weaning period, and produced heavier hot carcasses (57 lb; P < 0.05) than steers weaned from E+. Heifers weaned from NE+ tended (P < 0.10) to be heavier at weaning (39 lb). Heifer weight at breeding was only 22 lb heavier (P = 0.33) from NE+ vs. E+, but calving rates by heifers weaned from NE+ were much greater (P < 0.01) than those by heifers weaned from E+. Daily gains during post-weaning did not differ (P ' 0.33) between NE+ and E+ for steers or heifers. Therefore, grazing spring-born nursing calves on E+ prior to weaning has negative impacts that were not compensated for during later production stages on non-toxic feedstuffs.