Monensin and ammoniation or urea supplementation of bermudagrass hay diets for steers.

One growth trial using crossbred beef steers (297 +/- 2 kg, Exp. 1) and one metabolism trial using Holstein steers (405 +/- 14 kg, Exp. 2) were conducted to evaluate effects of ammoniation (3% of hay DM, added as anhydrous NH3) vs urea supplementation with or without monensin supplementation of mature \u27Alicia\u27 bermudagrass hay-based diets for steers. Ammoniation (P \u3c .05), but not urea (P = .26) or monensin (P = .70) supplementation, increased ADG in Exp. 1. In Exp. 2 ammoniation increased hay DMI (P \u3c .05), but urea (P = .88) or monensin (P = .16) had no effect. Supplementation with either monensin (P \u3c .05) or urea (P \u3c .05) decreased ruminal total VFA concentrations. Monensin also decreased the ruminal acetate:propionate ratio (P \u3c .001) and increased ruminal pH (P \u3c .05). Addition of urea to the concentrate supplement decreased the rate of concentrate intake. Both the rate (P \u3c .05) and the potential extent (P \u3c .001) of ruminal forage in situ DM and NDF disappearance were increased by ammonia treatment. Dietary interactions (P \u3c .10) were detected between monensin and ammoniation for rate and potential extent of in situ NDF disappearance and between monensin and urea supplementation (P \u3c .05) for ruminal total free amino acid concentrations. Decreased concentrations of VFA and lower forage digestibilities observed with monensin supplementation in Exp. 2 may explain the failure of monensin to affect ADG in Exp. 1