Effect of sub-therapeutic antibiotics and auction exposure on health, performance, and feeding behavior of weaned calves

Calves sourced directly from a ranch were heavier initially (273 vs. 258; P = 0.01) than calves from the same ranch but processed through an auction barn. For calves fed 6 g head-1 d-1 chlortetracycline from days 5 to 9, feeding an additional 350 mg head-1 d-1 of chlortetracycline and sulfamethazine from days 1 to 28 improved gain/feed (P = 0 .03), but only for the first 28 d of the 84-d trial. Frequency of bunk visits were altered by calf source and antibiotic treatment. Key words: Antibiotics, auction, calves, feedlot receiving programs