Liver abscesses are the primary liver abnormality of feedlot cattle at slaughter. The incidence of
liver abscesses is highly variable, but generally ranges from 10% to 20%. The incidence of total and the proportion of severely abscessed livers (A+) are greater in Holsteins fed for beef production and culled dairy cows than in beef breeds. The reason for the greater incidence of
liver abscesses in Holstein steers is not known, but one of the reasons is likely because of increased days on feed. The high prevalence in cull cows is likely because no specific intervention, such as use of
tylosin in the feed, is approved for use in dairy cows.
Liver abscesses are generally a sequela to ruminal
acidosis and rumenitis in cattle fed diets high in readily-fermentable
carbohydrates and low in
roughages; thus, the term "
acidosis-rumenitis-
liver abscess complex."
Liver abscesses are almost always
polymicrobial infections with Gram negative anaerobes constituting the predominant flora. Almost all studies have concluded that , a ruminal bacterium, is the primary causative agent and (formerly ) is the secondary pathogen. A limited number of studies have been done on the bacterial flora of
liver abscesses of culled dairy cows and Holstein feedlot steers. A recent study has reported on isolation of from
liver abscesses of Holstein cattle. The control of
liver abscesses in feedlot cattle has depended on the use of
antibiotics, particularly
tylosin, in the feed combined with sound nutritional management to minimize occurrence of
acidosis and subsequent rumenitis. Although there is no evidence of resistance development in , the future of
tylosin use as a feed additive in feedlot cattle is uncertain. Regardless, beginning January 2017, the use of
tylosin in feedlot cattle for the prevention of
liver abscesses will be under veterinary oversight. Although
tylosin is widely used in the feedlot industry, there is considerable interest in evaluating
antibiotic alternatives, such as
essential oils and
vaccines, to control
liver abscesses. Because
liver abscess is a
bacterial infection and the pathogenicity and
virulence factors of have been studied widely, there have been considerable interest and efforts to develop an efficacious
vaccine. The 2
antigens that have been targeted for
vaccine production are
leukotoxin and outer
membrane proteins of .