Bacterial flora of liver abscesses in crossbred beef cattle and Holstein steers fed finishing diets with or without tylosin

Holstein steers raised for beef production consistently have a higher prevalence and more severe form of liver abscesses than cattle of beef breeds. A study was conducted to compare bacterial flora of liver abscesses collected from multiple abattoirs from 4 groups of cattle, arranged in a 2 x 2 factorial design, consisting of crossbred cattle and Holstein steers, and each group fed a finishing diet supplemented with or without tylosin. A total of 383 liver abscess samples, consisting of 94 and 81 from crossbred cattle and 89 and 119 from Holstein steers fed finishing diets with or without tylosin, respectively, were subjected for anaerobic and aerobic bacterial isolations. The minimum inhibitory concentrations (MIC) of tylosin to the predominant bacterial species were determined. The likelihood chi-square test was performed to assess unadjusted differences in bacterial prevalence proportions between the 2 types of cattle (crossbred and Holstein steers) and feed type (tylosin or no tylosin). There was no interaction between cattle type and tylosin inclusion on the prevalence of any of the bacterial species isolated. Liver abscesses from Holstein steers yielded a higher total number of isolates compared to liver abscesses from crossbred cattle (1060 vs. 788). Fusobacterium necrophorum subsp. necrophorum was isolated from all abscesses. The prevalence of subsp. funduliforme was 19.1% and was not affected by the cattle type or tylosin. The prevalence of Trueperella pyogenes was higher (P < 0.01) in crossbred cattle (73.7%) compared to Holstein steers (29.8%). Also, the prevalence of T. pyogenes was higher in abscesses from tylosin-fed (66.1%) cattle than no tylosin-fed cattle (35%). The overall prevalence of Salmonella was 25.3% and was similar (P = 0.58) between cattle type, but the prevalence was lower (P < 0.01) in tylosin-fed (16.9%) compared to no tylosin-fed group (33%). Mean MIC of tylosin for F. necrophorum and T. pyogenes were similar across both cattle types and tylosin inclusion. Although bacterial flora of liver abscesses from Holstein steers appeared to be more diverse than that of crossbred cattle, there was no difference in the prevalence of the F. necrophorum and Salmonella, and in fact, prevalence of T. pyogenes was higher in crossbred than Holstein steers. Therefore, the difference in bacterial flora is not the likely reason for higher prevalence and severity of liver abscesses in Holstein steers than crossbred beef cattle.