PSV-28 Liver abscess microbiota of beef cattle administered in-feed tylosin differ according to abscess size and fraction

Abstract Liver abscesses (LA) pose a significant challenge to the Canadian beef industry as they are estimated to cost the industry ~ $61.2 million annually. This is likely an underestimate as it does not account for losses in animal productivity. Tylosin phosphate is widely used to reduce LA, but concerns over antimicrobial use selecting for antimicrobial resistance has created an urgency to explore alternative approaches. Understanding the impact of tylosin on the microbial ecology of LA is crucial to this. We hypothesized that altering the duration of in-feed administration of tylosin to feedlot cattle would alter the microbial community of LA. To investigate this, we collected abscessed livers from cattle fed a diet containing tylosin 1) throughout finishing, 2) during the first 78% of the feeding or 3) during the last 75% of the feeding period. We examined LA microbial ecology of purulent material, abscess capsule tissue, originating from abscesses of different sizes using a metataxonomic approach. Our findings revealed that shortening tylosin administration did not notably alter the alpha (P > 0.05) or beta-diversity (P > 0.05) of LA microbial communities. There was a significant difference in microbial richness associated with abscess capsule (P < 0.05) compared with bulk purulent material. Fusobacterium or Bacteroides ASVs dominated LA microbiomes, alongside probable opportunistic gut pathogens and other bacteria. Interestingly, classifying samples based on whether they originated from a liver with a single abscess, multiple abscesses or a very large abscess tended to differ in microbiome composition (P = 0.06). These insights contribute to our understanding of factors impacting liver abscess microbial ecology and will be valuable in identifying antibiotic alternatives. They underscore the importance of exploring varied approaches to address liver abscesses while reducing reliance on in-feed antibiotics.