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The objective was to evaluate the effects of tilmicosin fed to high-risk cattle for 14 consecutive days, with or without a live-yeast probiotic blend, during the 42-d study period. In Exp. 1, auction-derived bull (n = 59) and steer (n = 31) calves (initial BW = 220.3 ± 3.2 kg) were randomly assigned to 1 of 3 treatments (3 pens per treatment, 10 animals per pen) consisting of: 1) positive control (TUL) received ground corn top-dress as placebo and injectable tulathromycin on d 0, 2) Tilmovet (TV) received a tilmicosin supplemented diet (0.663 mg/animal/d) from d 0 to 14, and 3) TV with a proprietary live-yeast probiotic blend (TV+; 10 g/animal/d; OptiSafBeef, Phileo, Milwaukee, WI) for the duration of the study. The animals in the TUL group had a 7-d post metaphylactic interval (PMI) because they received injectable tulathromycin at d 0, whereas cattle in the TV and TV+ were eligible to be treated for BRD following 3-d post initial treatment of tilmicosin supplemented in the diet. The TUL group had greater ADG during the first 14-d (P = 0.02) and tended to be heavier than TV and TV+ on d 28 (P = 0.06). Overall (d 0 to 42), TV+ had greater (P = 0.02) G:F than TUL and TV. Overall DMI (P = 0.01) for the TUL group from d 0 to 42 was greater compared to TV and TV+. In Exp. 2, auction-derived bull (n = 68) and steer (n = 22) calves (initial BW = 219.4 ± 2.97 kg) were randomly assigned to treatment pens consisting of: 1) control (TUL) that received ground corn top-dress placebo, 2) Tilmovet (TV) that received a tilmicosin-treated diet (0.663 mg/animal/d) from d 14 to 28, and 3) TV with ground corn top-dress containing a live-yeast probiotic (10 g/animal/d; OptiSafBeef; TV+) for the duration of the study (Fig. 2.7). All treatments were administered ceftiofur on d 0 with a 3-d PMI. Final BW did not differ (P = 0.70). Total starch digestion had a day effect over the 2 collection days (P = 0.02), and a tendency (P = 0.09) was observed for apparent starch digestion to be greater for TUL on d 0. Performance and health outcomes were improved with the administration of injectable tulathromycin in Exp. 1, but there were no health differences and few performance effects noted in Exp. 2. Results indicate oral tilmicosin should not be the primary metaphylactic treatment method in high-risk beef cattle. Delaying oral tilmicosin for 14-d following an injectable antimicrobial slightly improved performance and health, but further research with larger pen replication needs to be conducted.



Agriculture, Animal Culture and Nutrition


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