Effects of feeding monensin to Holstein steers

Three experiments were conducted to determine the effects of monensin on feed intake, rate of gain and feed efficiency of a total of 198 Holstein steers. In experiment I, 72 steers were fed ground ear corn and corn silage diets containing 0 (treatment 1), 22 (treatment 2) and 33 (treatment 3) g/tonne DM monensin for 112 days. Treatments 2 and 3 received 11 g/tonne DM monensin for the first 28 days. Daily gains were not significantly different (P > 0.05) throughout the trial and intake was slightly reduced (P > 0.05) with monensin addition. Feed efficiency in treatments 2 and 3 were improved 5.5 and 8.8% respectively, but only treatment 3 was significantly (P 0.05) lower on treatment 2. Monensin improved (P > 0.05) feed efficiency by 8.5%. In experiment III, 40 purchased and 40 station-reared steers were assigned by origin, in pairs, to 40 Calan electronic headgates. A 23 factorial experimental design was used to evaluate the effect of diet with or without monensin used separately and in combination with progesterone-estradiol implants. Steers were fed a high moisture ear corn and corn silage diet for 84 days. No 3-factor interactions (P > 0.05) were detected. Implant treatments gained significantly (P