Submitted to: American Forage and Grassland Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2001
Publication Date: N/A
Interpretive Summary: Heat stress when transporting calves showing symptoms of fescue toxicosis can result in high mortality. Removing calves from tall fescue pasture and placing them on diets devoid of endophyte-infested tall fescue could precondition calves for the feedlot and reduce the combined effects of heat stress during transporting and fescue toxicosis. An experiment was conducted with endophyte-infested tall fescue to impose fescue toxicosis for yearling steers that were with or without implantation with an anabolic agent. The steers were placed in pens in early summer and feeding treatments of either free-choice bermudagrass hay or concentrate feed plus free-choice bermudagrass hay were evaluated. Two symptoms of fescue toxicosis, high rectal temperature and low serum prolactin concentration, were within normal levels after 3 to 4 days of being removed from endophyte-infested tall fescue pastures. Rates of change in these symptoms were not affected by previous implanting or diet. Results of the experiment show that implanted and non-implanted stocker calves exhibiting symptoms of fescue toxicosis can be removed and placed on a diet devoid of endophyte-infested tall fescue to reduce mortality rates and economic losses when transporting these calves to the feedlot. This approach can potentially improve the mortality of fescue calves being transported to feedlot and reduce the risk of suffering heavy monetary losses.
Technical Abstract: Heat stress can be a major problem in transporting stocker calves with symptoms of fescue toxicosis. It is possible to precondition calves grazed on tall fescue for transport to the feedlot by removing them from tall fescue and offering diets that are devoid of endophyte-infested tall fescue. An experiment was conducted that used a pasture phase to condition yearling steers to grazing tall fescue and induce symptoms of toxicosis, and a pen phase followed that determined the effects of previous implanting and level of nutrition (hay only versus hay plus concentrate feed) on short changes in rectal temperature and serum prolactin. Changes in rectal temperature and serum prolactin during the pen phase were not influenced by either implanting or level of nutrition. Rectal temperature declined linearly and were below a normal temperature by 82 h. Serum prolactin gradually increased and stabilized by 82 h. Results indicated that neither concentrate feeding or estrogenic implantation influenced recovery from fescue toxicosis, whereas removing calves from fescue pastures and excluding tall fescue from the diet for 3 to 4 d may alleviate symptoms of toxicosis.