331. Growth Performance of Backgrounding Steers Fed a Diet with Continuous or Intermittent Inclusion of Ergot Alkaloids with and Without a Mycotoxin Deactivating Product.

Abstract

This study evaluated the effect of feeding a backgrounding diet (60% barley silage:40% concentrate; DM basis) containing ergot alkaloids, with and without a mycotoxin-deactivating product (MDP), on the growth performance of feedlot steers. Crossbred steers (n = 360; 330 kg ± 24.03 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. The main factors were ergot exposure (none, continuous, or intermittent) and MDP inclusion (with or without). Dietary treatments consisted of: 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 84-d. Weights were recorded every 21 d. An ergot × MDP interaction was detected for dry matter intake (DMI) at 21 d on feed (DOF; P = 0.03), where IERG steers had 7.7% lower DMI than IEBN and COBN. No further effects of ergot exposure on DMI were observed, but MDP inclusion increased DMI by 3.9% at 42 DOF (P = 0.04; 7.74 vs. 7.45 kg/d). Steers fed control diets had greater ADG than those fed ergot continuously at 21 DOF (P = 0.05; 1.39 vs. 0.95 kg/d), with a similar tendency by 84 DOF (P = 0.06; 1.53 vs. 1.45 kg/d). Steers fed ergot intermittently did not differ from other treatments. The gain:feed was greater for control steers than continuously ergot-fed steers at 21 DOF (P = 0.03; 0.192 vs. 0.130), but no differences were detected thereafter (P ≥ 0.48). MDP inclusion did not affect ADG or gain:feed across the 84-d study (P ≥ 0.31). A tendency for an ergot × MDP interaction was observed for final BW, where IERG and CERB steers finished approximately 8 kg lighter than other treatments. In conclusion, 5 wk with no dietary ergot alkaloids allowed growth performance of cattle to recover after 1 wk receiving 2 mg/kg dietary ergot alkaloids during the first 21 d of backgrounding when impacts of ergot were most prevalent. Inclusion of MDP may help improve DMI during the first six weeks of the feeding period.