Bacterial Diseases
Bacteria are an uncommon cause of clinical liver disease in goats. Infectious necrotic hepatitis, or black disease caused by Clostridium novyi, is uncommon in goats compared to sheep.
The disease is discussed later in the chapter, in the section on fascioliasis, which predisposes to its occurrence. In this section, liver abscesses, which tend to be subclinical but can cause economic wastage due to liver condemnations, are discussed.Liver Abscesses
The syndrome of liver abscesses secondary to rumenitis that is well documented in feedlot cattle on high-energy rations has not been reported in goats thus far, even though there is increased interest in raising goats for meat under intensive or semi-intensive conditions. Sporadic cases of subclinical liver abscesses, however, do occur in goats and cause economic loss through liver condemnation at slaughter.
Etiology
A variety of organisms have been reported from caprine liver abscesses. Corynebacterium pseudotuberculosis is most common. Trueperella (Arcanobacterium) pyogenes and Escherichia coli are also common. Other sporadic !isolates include Proteus spp., Mannheimia haemolytica, Staphylococcus epidermidis, Staphylococcus aureus, Rhodococcus equi, Erysipelothrix rhusiopathiae, and the yeast Candida krusei (Whitford and Jones 1974; Eamens et al. 1988; Panebianco and Santagada 1989; Santa Rosa et al. 1989). The common bacterial isolate from bovine liver abscesses, Fusobacterium necrophorum, has been reported only once. This was from a single goat liver sampled during a slaughterhouse survey in Iran (Araghi-Sooreh and Firuzi 2011).
Epidemiology and Pathogenesis
No particular management, feed, or breed factors have been identified in the development of caprine liver abscesses. Reports of caprine liver abscess have come from Brazil (Santa Rosa et al. 1989), Botswana (Diteko et al.
1988), and Australia (Carrigan et al. 1988). In the Brazilian study, 2.5% of a necropsy study population showed liver abscesses. A greater proportion of adult goats was affected than young. Concurrent disease problems were always found, including caseous lymphadenitis, bronchopneumonia, rumen abscesses, peritonitis, and omphalophlebitis, among others. The association with concurrent infections suggests that liver abscesses probably occur from lymphatic or hematogenous spread from other loci of infection, but spread by parasite migrations through the liver is another possible cause.Das and Misra (1992) induced ruminal acidosis in goats by feeding high levels of rice and demonstrated that serum concentrations of the liver enzymes AST, ALT, and glutamate dehydrogenase (GDH) increased 24 hours following induction of rumen acidosis. They concluded that as in other species, ruminal acidosis can disrupt ruminal epithelial integrity and lead to entry of bacteria and fungi into the portal circulation, predisposing to the development of liver abscesses. This suggests that efforts to feed concentrates to meat goats under intensive conditions could lead to increased occurrence of liver abscesses.
Clinical Findings
There is one case reported from Trinidad in which an approximately 2-year-old Anglo Nubian doe with chronic weight loss was found to have a liver abscess caused by R. equi as the principal necropsy finding (Ojo et al. 1993). In all other reports to date, liver abscess in goats is either a subclinical finding or only one of several disease findings that could account for weight loss.
Clinical Pathology and Necropsy
Though not specifically reported in goats, elevation of liver-specific enzyme concentrations in the serum resulting from destruction of hepatocytes by expanding abscesses might occur. Abscesses may be detectable by ultrasonographic study of the liver, but would need to be differentiated from metacestode cysts. At necropsy, abscesses may be single or multiple, measure up to 5 cm in diameter, and contain purulent or caseous material.
Treatment and Control
There are no specific treatment or control recommendations. Appropriate therapy of concurrent disease problems may lead to some improvement in affected individuals. Efforts to control caseous lymphadenitis and omphalophlebitis in goats may be instrumental in reducing the frequency of liver abscesses. If concentrates are fed to meat goats, they should be introduced gradually into the foragebased diet and not provided in excessive amounts. The inclusion of antacids or buffers such as sodium bicarbonate in the ration also may be indicated to reduce the risk of ruminal acidosis, which could lead to liver abscesses.