South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Equids develop fat reserves when energy intake is above that required to maintain body condition.
This is a natural process, especially prior to onset of winter or during gestation, in order to prepare
the animal for periods during which energy demand will be increased. However, when energy
(feed) intake decreases suddenly and completely, mobilization of fatty acids from fat reserves can
lead to rapid increases in serum triglyceride concentrations (TG) that exceed the capacity of the
liver to process these energy substrates. Hypertriglyceridemia is defined as an elevation of TG
above the upper end of the reference range and minor increases in TG are common with many
diseases that result in a decreased appetite. The term hyperlipaemia is used when plasma becomes
grossly discoloured a milky white (Figure 3a), usually when TG exceed 1,000 mg/dL (11.3
mmol/L). Equids with hyperlipaemia often have a dull attitude and likely experience nausea that
further contributes to a poor appetite. Further, their livers can be markedly increased in size and
liver rupture (Figure 3b) and fatal haemorrhage into the abdominal cavity may occur. Treatment
requires provision of carbohydrate substrate, in the form of an intravenous dextrose solution
and/or forced enteral feedings via a nasogastric tube, as carbohydrates are needed for the liver to
process triglycerides. In conjunction with appropriate treatment of the underlying primary disease,
additional treatments that may be used to counteract hypertriglyceridemia include heparin and
insulin administration. Severe hypertriglyceridemia and hyperlipaemia can also develop in horses
with endocrinopathies including insulin resistance and pituitary pars intermedia dysfunction. Of
interest, equids with this complication of the endocrinopathy do not appear to have the severe
clinical signs observed in equids with other systemic disease, possibly due to the condition being
an alteration in metabolism in equids with endocrinopathies, rather than overwhelming hepatic
lipidosis.
Cholangiohepatitis and cholelithiasis: Horses with cholangiohepatitis can have weight loss / ill
thrift as the presenting complaint. In addition, recurrent colic, fever, and secondary
photosensitization may also be recognized. Physical exam of horses with cholangiohepatitis often
reveals a dull attitude but occasionally hepatic encephalopathy can also develop. Detection of
icterus is variable but, when present, supports liver disease. Clinicopathological assessment
reveals elevated hepatic enzyme activities allowing diagnosis of hepatic disease as the primary
Figure 3. Left: serum and plasma samples from an equid with hyperlipaemia; Right: liver of a pony that had
undergone two episodes of hepatic lipidosis – evidence of a “healed liver fracture” was found during necropsy
examination after unsuccessful treatment of the second episode of hyperlipaemia.
problem. Transabdominal ultrasonography is useful to assess liver size and presence of choleliths
in horses with liver disease (Figure 4). Obstructive disease (cholangiohepatitis with or without
associated choleliths) typically leads to an enlarged liver with a rounded edge that extends beyond
the costochondral junctions on the right side. A liver biopsy is relatively east to collect and
provides useful information for prognosis (extent of hepatic fibrosis).
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