Effect of mass medication with antibiotics at feedlot entry on the health and growth rate of cattle destined for the Australian domestic market.

OBJECTIVE To examine the effectiveness of mass medication with long acting antibiotics at feedlot entry on lot-fed Australian domestic cattle during a period of high risk for bovine respiratory disease (BRD). DESIGN Systematic allocation at feedlot entry of tilmicosin, long acting oxytetracycline or no antibiotic treatment, to cattle lot fed for the Australian domestic market. Comparisons of growth rate, disease occurrence and mortality were made between the groups at the conclusion of the feeding period. RESULTS Cattle medicated with tilmicosin at 10 mg/kg body weight on entry to the feedlot grew 0.08 kg/d faster than cattle medicated with oxytetracycline at 20 mg/kg body weight and non-medicated cattle. There was no significant difference in growth rate between oxytetracycline medicated cattle and cattle not medicated with antibiotic at feedlot entry. Cattle medicated with tilmicosin at feedlot entry had 8 fewer cases of disease per 100 animals compared with cattle not medicated with antibiotic at feedlot entry. There was no significant difference in disease occurrence between oxytetracycline medicated cattle and those not medicated with antibiotic at feedlot entry. CONCLUSION Mass medication with tilmicosin at feedlot entry of cattle destined for the Australian domestic market may be used to reduce disease occurrence and increase growth rate during periods of high risk for BRD.