318 Bovine liver abscess complex: Likely causes and tested solutions

Abstract

The liver abscess (LA) complex is commonly associated with high energy, limited roughage rations. Aggressive grain processing increases starch availability, leading to increased lactic acid production and lower rumen pH, potentially causing lactic acidosis. Rumen lesions may result from repeated bouts of lactic acidosis, likely allowing penetration of bacteria into the bloodstream, and have been associated with incidence of LA. Additionally, consumption of sharp objects can cause penetration of rumen epithelium and likely promote bacterial entry into the bloodstream. Research has successfully induced LA in both cattle and sheep from intraportal infusion of Fusobacterium necrophorum. F. necrophorum is a gram-negative, non-sporeforming anaerobe commensal to the rumen that likely enters the liver via the portal vein due to a damaged rumen wall. F. necrophorum has a plethora of virulence factors that support LA formation; however, recent research has indicated that LA contain polymicrobial cultures, and some have questioned if bacteria other than F. necrophorum can cause LA. Liver abscesses are not solely limited to animals on a high-energy diet; they have also been documented in cull beef-type and dairy-type cows. Production losses from LA are associated with reduction in dry-matter intake, average daily gain, gain:feed, live weight, hot carcass weight, dressed carcass yield, and subcutaneous fat depth, concomitant with increased carcass trim. To reduce the incidence of LA, cattle feeders typically include tylosin in the diet; multiple studies have reported a 20 to 38 percentage point reduction in the incidence of LA present at slaughter. Four additional antibiotics (bacitracin, chlortetracycline, oxytetracycline, virginiamycin) are approved for the prevention of LA. Feeding antibiotics to food animals is a contemporary social issue with limited societal support. Tested alternatives to antimicrobial control for LA include vaccination with F. necrophorum leukotoxoid or bacterin, feeding essential oils, enzymatic feed treatment, and feeding yeast fermentation products.