50. Growth Performance of Finishing Feedlot Steers Fed a Diet with Continuous or Intermittent Inclusion of Ergot Alkaloids with and Without a Mycotoxin Deactivating Product During Summer Months.

Abstract This study evaluated the effect of feeding a high-concentrate finishing diet (90% concentrate: 10% barley silage; DM basis) containing ergot alkaloids, with and without a mycotoxin-deactivating product (MDP), on the growth performance of feedlot steers. Crossbred steers (n = 360; 496 kg ± 35.34 kg) were stratified by body weight (BW) and randomly assigned to one of six treatments in a completely randomized design arranged as a 3 × 2 factorial. Main factors were ergot exposure (none, continuous, or intermittent) and MDP inclusion (with or without). Dietary treatments included: 1) control (CON; no ergot); 2) CON + MDP (COBN; 25 g/steer/d); 3) continuous ergot (CERG; CON + 2 mg total ergot alkaloids/kg DM); 4) CERG + MDP (CERB); 5) intermittent ergot (IERG; CERG diet for the first week of each 42-d period, followed by CON for 5 wk); and 6) IERG + MDP (IEBN). Steers were housed in 24 pens (4 pens/treatment; 15 steers/pen) and fed for 119-d. Weights were recorded every 21 d. After 63 d, all ergot-fed steers were switched to CON or COBN diets (MDP maintained) due to ergot induced hyperthermia. No ergot × MDP interactions (P ≥ 0.21) were detected. Steers fed ergot continuously had lower (P < 0.01) dry matter intake (10%; DMI) and BW throughout the study compared with control and steers fed ergot intermittently, and these reductions persisted even after ergot removal. Continuously feeding ergot reduced ADG through d 63 (20%; P < 0.01), followed by increased ADG from d 64 to 84 after ergot withdrawal (20%; P = 0.01). However, compensatory gain was insufficient, and these steers remained 20 kg lighter than control steers fed ergot intermittently at the end of the 119-d feeding period. The gain:feed ratio was reduced through d 63 (P < 0.01) but improved from d 64 to 84 (P < 0.01) for steers fed ergot continuously. However, no differences were observed over the entire feeding period (P = 0.12). Inclusion of MDP increased (P ≤ 0.02) DMI by 3.6% and ADG by 9.5%, and tended (P = 0.06) to increase the gain:feed ratio by 6.4% through d 42, regardless of ergot exposure, but provided no additional benefits thereafter. Intermittently feeding ergot did not adversely impact the growth performance of steers as much as continuous exposure. Continuously feeding ergot alkaloids reduced dry matter intake, ADG, and final BW of feedlot steers. The MDP improved growth performance during the first 42 d while ergot-contaminated diets were fed, but no benefits were observed beyond this point, likely due to the removal of ergot from diets after 63 DOF.