Effect of salinomycin or monensin on performance and feeding behavior of cattle fed wheat- or barley-based diets

Feeding behavior and growth performance of cattle fed diets containing mone nsin or salinomycin were assessed in two trials. In trial 1, 36 Hereford x Angus steers (267.7 +/- 4.3 kg) were individually fed (n = 12) wheat-based transition and finishing diets containing no ionophore (control, C), 26 mg monensin (M) or 13 mg salinomycin (S) per kg of dietary dry matter (DM). Ca ttle fed M consumed less than those fed C or S, and their intake was more s table during the transition to the finishing diet. Overall, steers fed M ex hibited lower dry matter intake (DMI) (8.0 vs. 9.2 and 9.2 kg d(-1)) and ra tes of gain (1.21 vs. 1.62 and 1.56 kg d(-1)) than those fed C or S. Cattle fed S required fewer days (93.3) to reach the targeted finish (5 min backf at) than those fed C or M (105.8 d). Monensin reduced slaughter weight and carcass weights, relative to controls (414.3 vs. 480.5 kg, and 231.2 vs. 24 5.8 kg, respectively). In trial 2, M (25 ppm) or S (13 ppm) were included i n barley-based diets for 72 yearling steers placed in four pens equipped wi th radio frequency identification systems. Individual bunk attendance patte rns were monitored during transition to a finishing diet, during I I d of l imit feeding the finishing diet twice daily (LF2/d), 13 d of limit feeding once daily (LF1/d), and 21 d of feeding once daily to ad libitum intake (AL 1/d). Ionophore type did not affect (P > 0.10) DMI, rate of gain or efficie ncy of feed conversion. Bunk visits were more frequent (P < 0.05) with M th an with S during transition and limit-feeding. With M, total daily attendan ce (TDA) at the bunk during LF1/d and AL1/d, was higher (P < 0.05) than wit h S, and variability in TDA was lower (P < 0.05) during LF1/d. In the prese nt study, there was no performance advantage in providing S or M in wheat-b ased finishing diets. Monensin moderated feeding intensity, but this effect may have been strong enough to suppress intake and even reduce gain on the wheat-based diet.