Effect of timing of tilmicosin metaphylaxis on control of bovine respiratory disease and performance in feeder cattle

Abstract

Four-hundred steer and bull calves at high risk of contracting bovine respiratory disease (BRD) were included in a 28-day study to evaluate various tilmicosin metaphylaxis programmes for the control of BRD in feeder cattle. The trial animals, which averaged 473 lb at purchase, came from multiple auction markets in the southeast USA over a 3 day period and were transported to a collection facility in West Point, Mississippi for treatment assignment. Following treatment assignment calves were randomly loaded onto trucks and transported to a research facility in Canyon, Texas. Calves were blocked by day of purchase and randomly assigned to one of four treatments in a randomized complete block design: (1) non-medicated controls, (2) metaphylactic treatment with tilmicosin at the time of treatment assignment (pre-shipment treatment), (3) metaphylactic treatment with tilmicosin at the time of processing at the research facility (post-shipment treatment), or (4) metaphylactic treatment with tilmicosin at the time of treatment assignment (pre-shipment) and 72 hours later (post-shipment) at the research facility (combination treatment). Tilmicosin was administered at 4.5 mg per lb (10 mg/kg) BW (7.1 ml) based on the average purchase weight. Data were analysed by analysis of variance using the General Linear Model procedure of SAS. The model included treatment, replication, and treatment x replication as sources of variation. The BRD morbidity rate was reduced in all tilmicosin metaphylaxis treatment groups as compared with controls (54, 29, 15, and 15% for treatments 1 through 4, respectively). Furthermore, BRD morbidity was reduced in the post-shipment and combination treatment groups compared to the pre-shipment treatment group. All calves experiencing clinical BRD during the trial were treated with tilmicosin at 4.5 mg per lb (10 mg per kg) BW, by subcutaneous (SC) injection. There was no difference between treatment groups in the treatment success rate for animals treated for BRD with tilmicosin. Bovine respiratory disease mortality was higher in the combination treatment group compared to the pre-shipment and post-shipment treatment groups (2, 0, 0, and 4% for treatments 1 through 4, respectively). There was no difference in average daily gain (ADG), dry matter intake, or feed/gain among any of the treatment groups during the 28-day study. Results from this study confirm that metaphylactic use of tilmicosin is an effective tool to control BRD in feeder cattle. Tilmicosin administered at the time of arrival processing (post-shipment) was superior to pre-shipment treatment. Combination treatment (both pre- and post-shipment) with tilmicosin did not further decrease BRD morbidity when compared to post-shipment treatment alone.