Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2001
Publication Date: N/A
Citation: Interpretive Summary: Heat stress when transporting stocker calves showing symptoms of fescue toxicosis can result in high mortality. Removing calves from tall fescue pastures and placing them on diets devoid of endophyte-infested tall fescue could precondition calves for transportation to the feedlot and reduce the mortality rate due to the combined effects of heat stress and fescue toxicosis. Information is needed to establish the minimum length for this preconditioning period and the effect of nutrition on heat stress symptoms. In this experiment steers that had grazed endophyte-infected tall fescue were placed in pens in early summer and fed either free-choice moderately low-quality bermudagrass hay or concentrate feed plus bermudagrass. Two symptoms of fescue toxicosis, high rectal temperature and low serum prolactin concentration, were within normal levels after 3 to 4 days of being moved from the endophyte-infested tall fescue pastures to the pens. The results are of interest to cattle producers because they demonstrate that removal of cattle from endophyte-infected for only a few days decrease symptoms of toxicosis which should reduce mortality and stress during transport to the feedlot.
Technical Abstract: Heat stress is a major problem in transporting stocker calves that exhibit symptoms of fescue toxicosis. Removing calves from tall fescue pastures and placing them on diets devoid of endophyte-infested tall fescue could reduce the severity of toxicosis and precondition calves for transporting to the feedlot. The pasture phase of the experiment was used to condition yearling steers to grazing tall fescue and induce symptoms of fescue toxicosis. The pen phase followed to determine the effects of implanting at the start of grazing and nutrition level (hay only versus hay plus concentrate) on short-term changes in rectal temperatures, serum prolactin concentrations, and white blood cell counts. White blood cell counts at the conclusion of the pasture phase averaged 8,778 cells/ L and were within a range indicating there was no immunological response. Initial rectal temperatures were high (average = 39.9 degrees C), but declined linearly over the first 5 d and were below a normal temperature (39.2 degrees C) by 84 h following removal from the tall fescue pastures. Serum prolactin gradually increased and stabilized by 82 hours following removal from tall fescue pastures. Changes in serum prolactin concentrations during the pen phase were not influenced by implanting or nutrition level. Results of the study indicate that calves grazed on endophyte-infested tall fescue and exhibiting symptoms of toxicosis can be preconditioned for transporting by removing the calves from tall fescue pastures and excluding tall fescue from their diets for 3 to 4 d, regardless of nutrition level of the diet or if the steers were implanted prior to grazing tall fescue.