Performance and Physiology of Steers Following Grazing of Toxic Tall Fescue as Influenced by Feeding Soybean Hulls on Pasture and Post-Graze Steroid Implantation

Authors: Aiken, Glen; MC CLANAHAN, L - KY COOP EXT. SERVICE; Kirch, Brett; SCHRICK, F - UNIVERSITY OF TENNESSEE

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2008
Publication Date: 10/1/2008
Citation: Aiken, G.E., Mc Clanahan, L.K., Kirch, B.H., Schrick, F.N. 2008. Performance and Physiology of Steers Following Grazing of Toxic Tall Fescue as Influenced by Feeding Soybean Hulls on Pasture and Post-Graze Steroid Implantation. Professional Animal Scientist. 2008. 24:392-398.

Interpretive Summary: Tall fescue is a cool-season perennial grass that is the predominant forage utilized for cattle grazing in a region east of the Great Plains between the temperate Northeast and subtropical Southeast. Unfortunately, an endophyte infects most tall fescue plants and produces ergot alkaloid toxins that induce fescue toxicosis. Symptoms of the malady include retention of rough hair coat, elevated body temperature, labored respiration, decreased serum prolactin, and poor weight gain. Post-graze performance and health of feeder calves that are background on toxic tall fescue is a major concern, but feeding supplements to cattle on fescue pasture and post-graze implantation with steroid hormones could improve performance, health, and well being. A two-phase (pasture and pen) experiment was conducted to evaluate the interactions effects of pelleted soybean hulls fed to steers on toxic fescue pasture and post-graze steroid implantation on body weight changes, dry matter consumption, rectal temperatures, and serum prolactin following removal from toxic tall fescue and placement on non-toxic diets. Feeding SBH on pasture boosted average daily weight gain; however, by the end of the pen phase, steers not fed on pasture but implanted with steroids had similar body weights to those fed on pasture. Regardless of feeding on pasture or post-graze implantation, rectal temperature rapidly declined to those indicative of a healthy animal in 4 d and serum prolactin increased and stabilized in 28 to 30 d. Physiology and well-being of cattle exhibiting fescue toxicosis are rapidly improved once they are placed on non-toxic diets. Cattlemen that retain ownership of feeder cattle background on toxic tall fescue can precondition these cattle by placing them on non-toxic diets prior to shipping to reduce morbidity and mortality in the feedyard.

Technical Abstract: A grazing experiment was conducted for 2 yr using a pasture phase to evaluate effect of feeding soybean hulls (SBH) on weight gain by steers grazing toxic tall fescue [Schedonorus arundinaceus (Schreb.)]. To evaluate carryover effects of feeding SBH on pasture and effect of post-graze steroid implantation on performance and physiology, steers were fed a non-toxic diet in a subsequent pen phase. Forty steers were assigned to 3.0-ha pastures that were assigned either with (n = 2) or without (n = 3) SBH (2.3 kg/steer/d, as fed). Following grazing, 36 steers were assigned to 9 pens and fed a corn silage-concentrate ration to compare: 1) effects of feeding SBH during the pasture phase and steroid implantation during the pen phase, 2) without SBH during the pasture phase and with steroid implantation during the pen phase, and 3) without SBH during the pasture phase and without steroid implantation during the pen phase. At the conclusion of the pen phase, steers without SBH on pasture and with post-graze implantation had greater (P < 0.05) ADG and BW than those without post-graze implantation. During the pen phase, rectal temperatures declined (P < 0.001) from above 40.2oC to less than 39.5oC in 4 d, and serum prolactin increased (P < 0.001) and stabilized in 28 to 30 d. Results indicate feeding SBH on fescue pasture can enhance weight gain and the physiology of cattle exhibiting toxicosis is improved once they are placed on-toxic diets.