Authors : D. K. Lunt, E. W. Hawkins and R. O. Kellems
Abstract: Five hundred seven bull calves were assembled at a commercial feedlot in North-central Utah and sorted by frame size into 8 pens. Bullocks were fed a high energy diet ad libitum. Approximately one-half of the bullocks received 27.5 mg/kg of sodium lasalocid daily while the others were fed 27.5 mg/kg of sodium lasalocid or sodium monensin on alternating days. The experiment was conducted with a randomized block design where ionophore treatment was the main effect and pens were blocks. The objectives of the study were to determine whether alternating two popularly used ionophores in feedlot diets affects average daily gain, efficiency of growth, total volatile fatty acid production, acetate to propionate ratio and/or carcass traits of young bulls. Bullocks were harvested by pen when the average fat thickness for a pen was estimated to be 0.6 cm. Days on feed averaged 126 days for all bullocks and were the same for each treatment group. No differences were detected (P<0.05) in average daily gain, dry matter feed to gain ratio, cost of gain, total volatile fatty acid production or acetate to propionate ratio. No treatment effects were found for carcass maturity scores, ribeye area, percentage of kidney, pelvic and heart fat or carcass weight. Fat thickness, marbling score and quality grade were slightly higher and USDA sex class was lower (P<0.05) for bullocks continuously fed lasalocid than for those fed lasalocid and monensin on alternating days. While small differences were observed for certain carcass traits, it was concluded that alternating ionophores in feedlot diets fed to young bullocks makes little difference in beef production traits of economic importance and is probably not cost effective.
Lunt, D. K. , E. W. Hawkins and R. O. Kellems , 2005. Alternation of Ionophores in Feedlot Diets Does Not Improve Daily Weight Gain, Efficiency of Growth or Carcass Traits of Bullocks . Journal of Animal and Veterinary Advances, 4: 90-93.