Effects of bambermycin or monensin offered in self-fed mineral supplements on performance of growing steer calves grazing small-grain pastures

Objective: Our objective was to evaluate feed additives in self-fed mineral supplements fed to steers grazing wheat (Triticum aestivum L.) pasture. Materials and Methods: In Exp. 1, steer calves in block 1 (n = 72, BW = 196 +/- 13.8 kg) and block 2 (n = 144, BW = 226 +/- 22.2 kg) were offered salt (SALT) or mineral mixtures that were nonmedicated (MIN) or contained 132 mg of bambermycin/kg (BAMB) ad libitum. In Exp. 2, steers in block 1 (n = 116, BW = 244.5 +/- 17 kg) and block 2 (n = 199, BW = 243.5 +/- 22 kg) were offered MIN, BAMB, or a mineral containing 1,786 mg of monensin/kg (RUM) ad libitum. Results and Discussion: In Exp. 1, MIN and BAMB did not differ (P = 0.69) but had increased BW and BW gains compared with SALT (P < 0.01). In Exp. 2 growth rate did not differ by treatment (P = 0.21), but at the end of grazing, RUM had greater (P = 0.01) BW than MIN and tended (P = 0.10) to be 12 kg heavier than BAMB. Implications and Applications: A complete mineral mixture is necessary to provide nutrients deficient in wheat pasture, and BAMB provided in a self-fed mineral mixture ad libitum did not improve performance. Monensin increased BW of steers through receiving and grazing. Monensin fed during receiving and grazing increases productivity of the stocker cattle enterprise.