Investigation of a Reduction in Tylosin on the Prevalence of Liver Abscesses and Antimicrobial Resistance in Enterococci in Feedlot Cattle

Abstract

Recent concerns over linkages between antimicrobial resistance in human pathogens and antimicrobial use in livestock have prompted researchers to investigate management strategies that reduce the current reliance on in-feed tylosin to control liver abscesses in feedlot cattle. A total of 7,576 crossbred yearlings were allocated to the study (∼253 animals/pen, 10 replicate pens per treatment) and individually randomized to one of three treatments. Tylosin phosphate (11 ppm) was included in-feed (1) for the first 125 days on feed (DOF) (FIRST-78%), (2) for DOF 41 to 161 (LAST-75%), or (3) for the entire feeding period (CON; day 0-161). Fecal composites were collected from the pen floor on days 0, 81, and 160 of the finishing period. Serial dilutions were spread plated for enumeration of enterococci on Bile Esculin Azide (BEA) agar and BEA amended with 8 µg/ml erythromycin. Results indicated that although the proportion of Ery R enterococci increased with DOF (P < 0.01), neither treatment (P = 0.34) or treatment × DOF (P = 0.37) affected antimicrobial resistance. Of the 538 isolates, 97% were enterococci, with mixed species isolated early in the feeding period and only Enterococcus hirae isolated at the end. Isolates were most frequently resistant to tylosin (86%), erythromycin (84%), and doxycycline (31%). Macrolide and tetracycline resistant isolates harbored erm(B), msrC, and tet(L), tet(M), tet(O) genes, respectively. Overall, the proportion of Ery R enterococci increased (P < 0.05) in all three treatments over the feeding period. Compared to the control cattle, FIRST-78% cattle had more severe (P < 0.05) liver abscesses, while there was a trend (P < 0.08) for this response in LAST-75% cattle. There was no difference (P > 0.05) in total liver abscesses, growth performance, carcass traits, morbidity, or mortality among treatments. These results support the potential to reduce the duration and therefore quantity of tylosin administered to feedlot cattle during the feeding period without impacting animal productivity.

Evaluation of the reticulorumen pH throughout the feeding period for beef feedlot steers maintained in a commercial feedlot and its association with liver abscesses

“…Those findings suggest that, in feedlot cattle, the greatest risk for liver abscess formation is during the early part of the feeding period. n In another study, 47 feedlot cattle that were fed tylosin phosphate for the first 125 DOF (first 78% of the feeding period) and between 41 and 161 DOF (last 75% of the feeding period) had more severe (A+) liver abscesses than did cattle that were fed tylosin phosphate continuously during feeding period.…”

Modeling the Effect of Tylosin Phosphate on Macrolide-Resistant Enterococci in Feedlots and Reducing Resistance Transmission

“…or macrolide resistance (Beukers et al, 2015;Müller et al, 2018;Davedow et al, 2020). Therefore, further field trials must examine the effect of standard feedlot diet changes in addition to the effect of TYL to improve our understanding of the interaction between diet and TYL effects.…”

Effects of age and pasture type on the concentration and prevalence of tetracycline and macrolide resistant Enterococcus species in beef cow-calf production system

“…(Lebreton et al, 2014;Cho et al, 2020;Agga et al, 2022a;Kaiser et al, 2022) Furthermore, enterococci have been reported from retail beef (Tyson et al, 2018), retail veal meat (Tate et al, 2021), and ground beef (Vikram et al, 2018;Schmidt et al, 2021) suggesting their foodborne implications. Antimicrobial resistance of enterococci have been extensively studied in feedlot cattle (Vikram et al, 2017;Davedow et al, 2020;Murray et al, 2022), dairy cows (Shipp and Dickson, 2012;Abdelfattah et al, 2021), and to a lesser extent in cull cows. (Pandit et al, 2021) However, such studies are rare in beef cow-calf (Agga et al, 2016) and backgrounding operations (Agga et al, 2019).…”