The effects of feeding monensin and lasalocid together in the same diet or in a daily rotation program on performance and carcass characteristics of feedlot cattle

Two hundred and seventy-five Charolais cross steers housed in 25 pens were used to study the effects on feedlot performance of feeding monensin and lasalocid combined in the same diet or in a daily rotation program. Five dietary treatments were utilized. Formulated ionophore concentrations were: (1) monensin at 11 ppm for the first 28 d of the trial and 33 ppm for the remainder; (2) monensin at 16 ppm plus lasalocid at 18 ppm; (3) monensin at 16 ppm for the first 28 d of the trial and 25 ppm for the remainder plus lasalocid at 27 ppm; (4) lasalocid at 36 ppm; (5) daily rotation of diets 1 and 4. Feeding monensin and lasalocid together in the same rotation (diets 2 and 3) or in a daily rotation program (diet 5), did not (P > 0.05) improve feedlot performance or carcass characteristics compared to steers continuously fed monensin or lasalocid (diets 1 or 4). Direct comparison of the two control diets demonstrated that lasalocid-fed steers exhibited more efficient gains (P < 0.05) at day 28 of feeding and a higher dressing percentage (P < 0.05) at slaughter. These results indicate that relative to continuous feeding of monensin or lasalocid, feedlot operators would not benefit by combining these two ionophores in the same diet or by incorporating daily ionophore rotation into their feeding programs. Key words: Ionophores, monensin, lasalocid, steers