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Effects of in-feed chlortetracycline prophylaxis of beef cattle on animal health and antimicrobial-resistant Escherichia coli

Getahun E Agga, John W. Schmidt, Terrance M. Arthur
Applied and environmental microbiology 2016 v.82 no.24 pp. 7197-7204
Escherichia coli, animal health, antibiotic resistance, beef cattle, cephalosporins, chlortetracycline, disease control, feedlots, feeds, long term effects, medicine, morbidity, tetracycline
Concerns have been raised that in-feed chlortetracycline (CTC) may increase antimicrobial resistance (AMR), specifically tetracycline-resistant (TETr) Escherichia coli, and third-generation cephalosporin-resistant (3GCr) E. coli. We evaluated the impact of a 5-day in-feed CTC prophylaxis on animal health, TETr E. coli, and 3GCr E. coli. A "control group" of cattle (n = 150) that received no CTC, while a "CTC group" (n = 150) received in-feed CTC from the 5th to the 9th day after feedlot arrival. Fecal swab and pen surface occurrences of generic E. coli (E. coli regardless of AMR status), TETr E. coli, and 3GCr E. coli were determined on five sample occasions: arrival at the feedlot, 5 days post treatment completion (5 dpt), 27 dpt, 75 dpt, and 117 dpt. On 5 dpt, TETr E. coli concentrations were higher for the CTC group than control group. On 27 dpt, 75 dpt, and 117 dpt TETr E. coli concentrations did not differ between groups. 3GCr E. coli occurrences did not differ between control and CTC groups on any sample occasion. Cattle morbidity and therapeutic use of antimicrobials critically important to human medicine were lower for the CTC-treated group. For both groups generic, TETr, and 3GCr E. coli occurrences were highest on 75 dpt and 117 dpt, suggesting that factors other than in-feed CTC contributed more significantly to antimicrobial-resistant E. coli occurrence. In conclusion, a 5-day in-feed CTC treatment reduces morbidity and therapeutic antimicrobial use in feedlot cattle with no long-term impact on the occurrence of antimicrobial-resistant E. coli. occurrence.