Comparison of gamithromycin post-treatment intervals for beef cattle naturally affected with bovine respiratory disease
The primary objective of this study was to compare different gamithromycin post-treatment intervals (PTI) on clinical health outcomes in cattle naturally affected with bovine respiratory disease (BRD). Eight hundred cattle identified with BRD by pen riders, rectal temperature ≥ 104.0°F (≥ 40°C), and no previous treatments were randomized in a 1:1:1:1 ratio to 3-, 6-, 9-, or 12-day PTI within each lot. Cattle treated for BRD were returned to their home pen, and followed for 60 days (d) to monitor subsequent health outcomes. Cattle were categorized by type (dairy-beef or native). General and generalized linear mixed models were used for statistical analyses. First treatment success (P = 0.012) and BRD case fatality risk (P = 0.032) were different among PTI groups. The 9-d PTI group had the greatest first treatment success, which was different (P = 0.008) than the 3-d PTI. The 12-d PTI group had the poorest BRD case fatality risk, which was different (P = 0.071) than the 9-d PTI group. There were no significant differences between the 6- and the 9-d PTI groups. Dairy-beef cattle had an approximately 2-fold higher BRD case fatality risk (P = 0.012) than natives. Results will help practitioners to optimally use gamithromycin in the field.