Wednesday, November 15, 2006 - 9:15 AM

Post-Graze Performance and Recovery from Heat Stress for Yearling Steers Grazed on Toxic Tall Fescue.

Glen Aiken1, Linda McClanahan2, and Brett Kirch1. (1) USDA-ARS, Forage-Animal Production Research Unit, N-220 Ag. Science North, Lexington, KY 40546, (2) University of Kentucky, 222 Ag. Science North, Lexington, KY 40546

Cattle grazed on toxic tall fescue (Festuca arundinacea) consume ergot alkaloids that can lead to “fescue toxicosis”.  The alkaloids can be diluted with concentrates to improve weight gains, but it is uncertain if dilution can affect subsequent feedyard performance.  A 2-yr experiment determined if feeding soybean hulls (SBH) on fescue pasture and post-graze implantation with steroidal hormones could affect post-graze changes in rectal temperature (RTEMP), prolactin (PROL), body weight (BW), and dry matter (DM) consumption.  Steers were grazed during the summer using five, 3.0-ha pastures (2.7 steers ha-1) of ‘KY-31’ fescue assigned either SBH (n = 2; 2.3 kg steer-1 d-1, as fed) or pasture-only (n = 3) treatments.  At conclusion of grazing, steers were assigned to pens and fed a corn silage-concentrate mixture.  Treatments of SBH on pasture with post-graze implantation, pasture-only with post-graze implantation, and pasture only without implantation were assigned to pens in a completely randomized design (3 replications).  Periodically during the pen phase, BW and RTEMP were recorded and blood was collected.  Orts were measured weekly to estimate DM consumption (kg DM 100 kg-1 BW).  Within both yr, RTEMP for both pasture treatments was initially high but declined and stabilized (P < 0.001) in 5 d, and PROL increased and stabilized in 20 d.  Steers fed on pasture had greater (P < 0.01) BW than the pasture-only group at the conclusion of grazing.  At conclusion of the pen phase, implanted steers tended (P < 0.10) to have greater BW than pasture-only steers.  Consumptions increased and stabilized (P < 0.05) in 20 d for 2004 and 30 d in 2005.  Feeding SBH to steers on toxic fescue will reduce time to alleviate heat stress and adjustment to non-toxic diets.  Furthermore, feeding SBH on pasture and combined with post-graze implantation can reduce time in the feedyard.