Submitted to: Southern Pasture and Forage Crop Improvement Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 16, 2007
Publication Date: May 29, 2007
Citation: Aiken, G.E. 2007. Management of Cattle to Reduce Vulnerability to Heat Stress Following Grazing of Toxic Tall Fescue. 61st Southern Pasture and Forage Crop Improvement Conference Proceedings, May 30-June 1, 2007, in Tallahassee, FL. 2007. pg 54-57. Technical Abstract: Tall fescue is primarily utilized for cow-calf production because poor weight gain efficiency of calves exhibiting fescue toxicosis has prevented the wide use of tall fescue for stocker production. Most calves weaned on tall fescue pastures and not retained for herd replacement are typically sold and transported to other regions for pasture backgrounding while some are retained for shipment to feedyards. Fescue toxicosis exacerbates the stress from shipping and these combined stresses can increase morbidity and mortality, and the length of feedyard adjustment. Management strategies, such as preconditioning, could reduce stress levels of fescue cattle that are transported long distances. Thus far, experiments have indicated that cattle can be removed from toxic tall fescue pastures to lower elevated body temperatures in 3 to 12 d. Number of days needed for rectal temperatures to decline to those of a healthy and stabile condition will depend on ambient temperatures. Longer recoveries from elevated body temperature appear to be required if ambient temperatures are above 25°C. Serum prolactin increases and stabilizes in 2 to 20 days after toxins are removed from the diet. Time for prolactin concentrations to increase and stabilize may also depend on ambient temperature. Other factors are the extent of time on toxic tall fescue pasture, pasture infection of stands, and alkaloid concentrations in grazed fescue. Changes in physiology of cattle as they switch from toxic to non-toxic diets appear associated with the excretion of alkaloids and the reduction of alkaloid concentrations in vascular circulation. High affinities of alkaloids at receptors likely slows their diffusion. More research is needed to determine possible storage and release of ergot alkaloids in organs and other tissues and evaluate long-term carryover effects of alkaloids on cattle physiology.