Abstract
Liver abscesses (LA) in cattle are a major issue in the beef industry, particularly in beef-on-dairy cattle, because of their economic impact on performance, liver condemnation, carcass yield and characteristics. Fusobacterium necrophorum subsp. necrophorum is the primary etiologic agent, but three other pathogens, F. necrophorum subsp. funduliforme, Trueperella pyogenes, and Salmonella enterica, are often prevalent. It is theorized that ruminal epithelium damaged by chronic acidity becomes susceptible to bacterial invasion, which then enter portal circulation to reach the liver. Nucleic acid sequence-based analyses have indicated bacterial DNA in healthy, livers of cattle suggesting that livers harbor a resident bacterial community. Our study aimed to detect, quantify and isolate the four LA pathogens from healthy livers (HL), normal tissues of abscessed livers (NL) and ruminal epithelial tissues (HRT and NRT). A total of 419 liver and ruminal epithelial tissue samples (107 HL, 110 NL, 101 NRT and 101 HRT) were collected from beef-on-dairy cattle at slaughter. Samples were homogenized and subjected to a 4-plex real-time quantitative PCR assay (qPCR) to detect and quantify culture methods to isolate the four LA pathogens. Samples negative by qPCR or isolation before enrichment were also enriched in lactate and lysin broths made selective by adding josamycin, vancomycin and norfloxacin. Data was analyzed with liver (HL or NL) and ruminal epithelial tissue status (HRT or NRT) as the fixed effect and Fisher’s exact test to assess prevalence of the pathogens and a t-test to assess log-transformed bacterial concentrations (Table).These findings indicate that these pathogens are present in uninfected liver tissues, suggesting regular bacterial flow from the gut to the liver, potentially allowing colonization to levels that overcome liver defenses and initiate abscess formation.