Investigation of an in-feed reduction of tylosin on the prevalence and severity of liver abscesses, antimicrobial resistant enterococci and productivity in feedlot cattle
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Date
2019
Authors
Davedow, Taylor
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Abstract
The primary objective of this work was to assess alternative feeding strategies on liver abscesses, growth performance, carcass traits, and immune responses in beef cattle as well as to characterize antimicrobial resistance in enterococci isolated from cattle feces. In the first study, cattle (n = 90) were randomly assigned to 6 treatments (n = 15/treatment): 1) control, 2) low (12 g Saccharomyces cerevisiae fermentation product (SCFP) •steer-1•d-1), 3) medium (15 g SCFP•steer-1•d-1), 4) high SCFP (18 g SCFP•steer-1•d-1), 5) encapsulated SCFP (eXPC; 7 g XPC•steer-1•d-1), and 6) antibiotics (ANT; 330 mg monensin + 110 mg tylosin•steer-1•d-1). In the second study, cattle (n = 7576; ~ 253 animals/pen, 10 replicate pens per treatment) were randomized to 3 treatments: tylosin phosphate (11 ppm) in-feed 1) for the first 125 days on feed (DOF) (FIRST-78%), 2) for DOF 41 to 161 (LAST-75%), or 3) the entire feeding period (CON; day 0 to 161). Increasing SCFP tended (P < 0.09) to linearly increase feed efficiency. Average daily gain (ADG) tended (P < 0.10) to be greater in steers supplemented with eXPC than control. The percentage of erythromycin resistant (EryR) and erythromycin + tetracycline resistant enterococci was greater (P < 0.05) with ANT than control, SCFP and eXPC, while tetracycline resistant enterococci was not affected. Isolates were most frequently resistant to tylosin (86%), erythromycin (84%) and doxycycline (31%). Macrolide resistant isolates harbored primarily erm(B), msrC and tetracycline resistant isolates tet(L), tet(M), tet(O) genes. Cattle administered tylosin for a shorter duration had a greater risk of severe liver abscesses compared to controls; but there was no difference in risk of total liver abscesses, growth performance, carcass traits, morbidity or mortality. The proportion of EryR enterococci increased in all treatments over the feeding period. These studies support the potential to feed SCFP, eXPC or tylosin for a reduced duration as an alternative to the continuous administration of tylosin. This study emphasizes the importance of continued research into feeding regimens that promote antimicrobial stewardship, while maintaining the productivity and health of feedlot cattle.
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Keywords
Tylosin, Antimicrobial, Cattle, Resistance, Beef