Effects of potential Tylosin substitutes on Salmonella prevalence and the microbiome of subiliac lymph nodes of beef feedlot cattle

2017 Summer.Includes bibliographical references.Tylosin, a macrolide antibiotic, is fed to feedlot cattle for liver abscess prevention. Tylosin alternatives are currently being investigated as pressures to reduce the amount of antibiotics used in livestock increase. Understanding effects of various feeding strategies on the safety of beef products is a priority as alternatives are investigated. This study investigated the effect of Tylosin, and two Tylosin alternatives on the prevalence of Salmonella in subiliac lymph nodes (SLN) and the microbiome of SLN from feedlot cattle. Salmonella harborage in the lymph node is a challenge for the beef industry as ground beef is made from beef trimmings that commonly contain lymph nodes. Consumption of contaminated ground beef is one of the possible foodborne routes of Salmonella infection. SLN (n=600) were collected from feedlot cattle (n = 5,481) at the time of slaughter. Overall 84.6% of the SLN were positive for Salmonella and the treatment did not influence prevalence (P > 0.8402). Samples from each pen of feedlot cattle (15 SLN/pen) were composited for microbiome analysis using 16s rRNA amplicon sequencing. Samples were analyzed using the open-source software Quantitative Insights Into Microbial Ecology (QIIME). The treatment did not influence the microbiome of the SLN (P = 0.223; P= 0.267). The top three phyla present were Proteobacteria (67.3%), Actinobacteria (10.2%), and Acidobacteria (9.5%). Although Salmonella was culturally isolated, it was not identified in the microbiome analysis because the genus could not be resolved for 18.9% of the Enterobacteriaceae family. Understanding why Salmonella is detectable in the lymph nodes may hold the key for prevention, and characterizing the microbiome is crucial for this process