Page 923 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

898 CHAPTER 5

VetBooks.ir 5.21 doxycycline (10 mg/kg p/o q12–24 h) and metroni-
dazole (20–25 mg/kg p/o q12 h). Duration of ther-
apy may be judged according to progress assessed
clinically as well as by inflammatory markers, ultra-
sound and repeat biopsy. Foals with Tyzzer’s disease
should be treated aggressively with sodium benzyl
penicillin (50,000 IU/kg i/v q6 h) or oxytetracycline
(10 mg/kg i/v q12 h).
Fascioliasis may be treated with triclabenda-
zole (12–15 mg/kg p/o), which may possess activity
against both adults and larvae, although resistance
may be common. Closantel, a drug toxic to adult
Fasciola, has been used as an alternative agent for
Fig. 5.21 A typical large cyst and a less typical fascioliasis in donkeys, although safety has not been
smaller anechoic cyst in the liver of a mature pony established in horses.
affected by cystic echinococcosis. The deeper, less CE is generally well tolerated and not associ-
distinct anechoic structure is the hepatic portal vein. ated with impaired liver function. However, when
numerous hydatid cysts are seen and suspected to
be contributing to disease they may be treated with
Biopsy will generally be helpful for both firm albendazole (10 mg/kg p/o q24 h for 2–3 months) or
confirmation of bacterial hepatitis and also for cul- by cyst aspiration and injection of sterile saturated
ture of causal organisms. Similar changes may be saline into the cyst cavity. Praziquantel has also been
seen in fascioliasis, although the focal nature of advocated in human medicine at a dose of 25–50
infections may lead to non-specific or even normal mg/kg once or twice weekly alone or in addition to
biopsy findings. Other than the extensive necrosis albendazole.
seen in Theiler’s disease cases, other forms of puta-
tive viral hepatitis are still poorly recognised and Prognosis
without definitive histopathological features. Tyzzer’s disease in foals and Theiler’s disease in
adult horses are associated with high mortality rates.
Management In contrast, conditions such as hepatic nematode
Bacterial hepatitides in mature horses may involve migration or CE are generally subclinical. For other
a variety of aerobic, anaerobic, gram-positive and infectious hepatitis cases discussed above, the prog-
gram-negative bacterial speciesand therefore broad- nosis is highly variable depending on the extent of

spectrum antibacterial therapy is essential, unless disease.
a specific single species is isolated and targeted.
However, even if a single pathogen is successfully NEOPLASTIC LIVER DISEASE
isolated from culture of biopsy specimens there is
always a strong possibility that other coinfectors Definition/overview
were present but did not survive the culture pro- Hepatic neoplasia is rarely encountered in horses
cess. In mature horses, drug selection and dose are although the liver can be an occasional site of both
influenced by factors including hepatic metabolism primary and metastatic neoplasms.
and likely target bacterial species, but inevitably the
choice of drug is also heavily biased by the require- Aetiology/pathophysiology
ment for prolonged therapy (typically for at least 4–8 Biliary carcinoma, lymphoma, haemangiosarcoma,
weeks). Therefore, antibacterials suitable for enteral hepatocellular carcinoma (Figs. 5.22, 5.23) and
administration are preferred including potentiated hepatoblastoma are the most common primary

sulphonamides (30 mg/kg combined product p/o tumours. Squamous cell carcinoma and melanoma are
q12–24 h), enrofloxacin (5–7.5 mg/kg p/o q24 h), the main causes of metastatic neoplastic liver disease.