Feedlot growth performance of steers on salinomycin, monensin and a daily rotation between the two

The effects of salinomycin (20 mg kg-1 feed), monensin (33 mg kg-1 feed) and a daily rotation of these ionophores, on average daily gain (ADG), average daily feed intake (ADFI) and feed conversion efficiency (FCE) were investigated in 60 steers (273 kg) over an 84-day feedlot period. Individual feed intakes and weight gains were recorded. The data were fitted to linear regressions with individual animals as replicates, from which ADGs, ADFIs and FCEs were calculated. Means of parameters of the control, salinomycin, monensin and rotation treatments were respectively ADG (kg): 1.56, 1.74, 1.58 and 1.66; FCE (kg DM/kg): 5.83, 5.43, 5.53 and 5.38; ADFI (kg): 9.10, 9.43, 8.83 and 8.90; final weight (kg): 402, 419, 407 and 413. Salinomycin showed the greatest improvement in gain, whereas monensin did not affect gain and tended to decrease feed intake. The rotation programme did not result in added benefits above those that could be obtained with a single ionophore (salinomycin), although feed efficiency tended to increase.