| Popis: |
Objective No antimicrobial, tilmicosin, or tildipirosin were evaluated for the control of bovine respiratory disease (BRD), and additional days on feed (DOF) were evaluated for effects on growth performance and carcass characteristics of Mexican-origin steers. Materials and Methods A split-plot design was used with 2 DOF treatments nested within 3 metaphylaxis treatments. Steers originating from Mexico (n = 4,086; 213 ± 31.2 kg) were randomly assigned to on-arrival metaphylaxis treatments: 1) no antimicrobial (CON), 2) 13.2 mg/kg tilmicosin (MIC), or 3) 4 mg/kg tildipirosin (ZUP). Ten pen replications per metaphylaxis treatment were used (30 pens). Approximately 30 to 45 d before projected slaughter date, steers were randomly assigned within each of the 30 pens to 1 of 2 DOF (sort groups) treatments shipped for slaughter 28 d apart: 1) early slaughter averaging 50 d (range: 46 to 63 d) after the sort or 2) late slaughter averaging 78 d (range: 74 to 91 d) after the sort, resulting in 60 pens. Results and Discussion Metaphylaxis with MIC (5.56%) or ZUP (3.58%) reduced (P Conclusions and Applications Metaphylaxis improved animal health compared with no metaphylaxis, and tildipirosin improved morbidity but not mortality compared with tilmicosin. Live growth slowed but live and carcass weight increased with additional DOF. Carcass characteristics indicated increased marbling and fatness occurred with additional DOF. |
