Performance and Physiology of Yearling Steers Grazing Toxic Tall Fescue as Influenced by Feeding Soybean Hulls and Implantation with Steroid Hormones.

An endophyte (Neotyphodium coenophialum) that infests tall fescue (Lolium arundinaceum) produces ergot alkaloids that adversely affect performance and physiology of cattle to inflict a malady collectively termed ‘fescue toxicosis’.  A two-yr grazing experiment was conducted with yearling steers grazed on toxic ‘Kentucky-31’ fescue to determine if feeding soybean hulls (SBH) can be combined with steroidal implantation to increase weight gain and mitigate the effects of toxicosis.  Sixty-four steers were grazed from 7 May to 5 July in 2008 and sixty steers were grazed from 29 April to 24 June in 2009.  Steers were assigned to six, 3.0-ha toxic fescue pastures.  Treatments were assigned using a split-plot design, with the main plot treatment being with or without SBH, and the split-plot treatment being with or without ear implantation with steroid hormones (200 mg progesterone-20 mg estradiol).  Implant treatments were assigned to two subgroups within each pasture.  Pelleted SBH were group-fed to provide daily consumption of 2.3 kg steer^-1 (as fed).  Unshrunk bodyweights were measured at initiation and at 28-d intervals. Jugular blood was collected at day 56 and on the final day of grazing for assaying serum prolactin, and hair coats were rated on the final day as being rough, transitional, or sleek. Average daily gain was highest (P < 0.05) with the combining of SBH and implantation (1.23 kg d^-1), and was higher for SBH (0.95 kg d^-1) than for implantation (0.81 kg d^-1).  Prolactin concentrations were not affected (P > 0.10) by implantation, but were greater (P < 0.001) with than without SBH.  Steroid implantation also did not affect (P > 0.10) hair coat ratings, but there was lower frequency of rough hair coat ratings with (44%) than without (61%) SBH.  Results indicated that combining SBH with steroid implants can substantially increase weight gain of calves grazed on toxic fescue, and that SBH can reduce the severity of toxicosis.