The Effect of Tylosin Supplementation and Tylosin Alternative Control Treatments on Fecal Microbial Populations, Performance, and Liver Abscess Prevalence in Feedlot Cattle.

Currently, there is significant public and private pressure to reduce and find alternatives for antibiotics used in animal production. Tylosin phosphate, a macrolide commonly used to reduce and prevent liver abscesses in feedlot cattle, has come under intense scrutiny for its widespread use in cattle feeding. The potential removal of Tylosin from cattle feeding could have a marked impact on the beef industry. Thus, investigating Tylosin alternatives is imperative. In light of this, a blinded, randomized, controlled field trial was conducted to evaluate the effect of Tylosin and two alternative treatments on fecal microbial populations, feedlot performance, and the prevalence of liver abscesses in feedlot cattle. Commercial steers and heifers (n = 5,481 hd) from similar sources were placed on feed at a commercial feedyard in Texas. Ten 4-pen blocks (40 pens) were assembled beginning in March 2016. At placement, cattle were randomly assigned to one of four treatment groups: 1) Finishing ration with Tylosin (90 mg/hd/d) fed until harvest (Tyl); 2) Finishing ration without Tylosin or other treatments (NTyl); 3) Finishing ration without Tylosin, but with an essential oil fed until harvest (EsOil); or 4) Finishing ration without Tylosin but with a yeast fermentation by-product (18 g/hd/d) fed until harvest (SCP). A composite fecal sample was obtained from each pen floor within four weeks of placement and again two to four d prior to harvest in order to evaluate fecal microbial populations and obtain isolates of Salmonella enterica, Enterococcus, and non-type-specific Escherichia coli for further characterization. At the conclusion of the finishing period, cattle were harvested at a commercial processing facility. Livers were evaluated for abscess prevalence and severity scoring at harvest. Additionally, a subset of livers from each pen (n = 5/pen) were collected for analysis of the microbial population using traditional culture-based techniques in addition to 16S rRNA gene sequencing to evaluate the microbiome Although previous data and results from the current study highlight the utility of Tylosin inclusion on the reduction of liver abscesses, investigating alternatives is a necessity for the beef cattle industry. Furthermore, understanding the influence of these alternatives of microbial populations will not only aid in improving their efficacy, but also assuring the safety of the beef food chain. This understanding will be imperative for the future implementation of strategies aimed to mitigate liver abscesses and maintain the safety and economical production of beef.