Effects of two different doses of tilmicosin on pathogen load reduction and clinical outcome in feedlot cattle with naturally occurring bovine respiratory disease

Abstract

The objective of this study was to determine the effect of 2 different doses of tilmicosin on pathogen load reduction and clinical outcome in feedlot cattle experiencing acute bovine respiratory disease (BRD). Cattle diagnosed with BRD were randomly assigned to 1 of 3 treatments: tilmicosin at 4.55 mg/lb (10 mg/kg) (TIL10); tilmicosin at 9.1 mg/lb (20 mg/kg) (TIL20); or untreated positive controls (POSCON). Cohorts were completed with an apparently healthy asymptomatic negative control (ASYMP). A total of 143 animals were enrolled in the study. Treating cattle with tilmicosin at 9.1 mg/lb (20 mg/kg) resulted in greater pathogen load reduction and equivalent or improved clinical response compared to a dose of 4.55 mg/lb (10 mg/kg). Cattle in the TIL10 and TIL20 treatments had reduced pathogen loads and increased survival rates compared to POSCON (P less than 0.05). The Mannheimia haemolytica numbers in the lungs were significantly reduced in the TIL20 treatment group on day 9 compared to TIL 10 (P less than 0.05). Survival of calves in the TIL10 and TIL20 groups did not differ (P greater than 0.05) from ASYMP, but was decreased (P less than 0.05) in POSCON calves compared to other treatments.