South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Figure 2. Tansy ragwort (Senecio jacobaea) is a biennial plant that when mature has yellow flower clusters atop
stout, leafy elongated stems that can grow up to 6 feet tall (left); tansy ragwort usually germinates in fall or early
winter and lives through the first year as a rosette (centre); the plant matures the following year and has leaves that are
dark green on top and whitish-green underneath with deeply cut, blunt-toothed lobes with a ragged/ruffled
appearance; bright-yellow flowers (usually with 13 petals) and seeds are produced in the late summer and fall months
(images from www.agf.gov.bc.ca/cropprot/weedguid/tansyrag.htm)
A history of exposure to either clover or ragwort is clearly important to determine in the
evaluation of horses presented with chronic weight loss, icterus, and photosensitization. However,
it is not uncommon for owners to be unaware of exposure to these plants and the pasture may
need to be examined by an extension agent or hay samples may need to be examined for
contamination with these plants. Although abnormalities detected on physical examination and
laboratory analysis of blood samples may not differ markedly with these two intoxications, further
examination of the liver typically shows substantial differences. Specifically, with clover toxicity
the liver may be normal in size to enlarged with rounded margins on ultrasonographic
examination while the liver is more often small with ragwort intoxication. This difference likely
reflects a more prolonged and insidious course of liver damage with ragwort in comparison to a
more subacute insult with clover. Next, histopathological examination of hepatic biopsy samples
reveals bile duct proliferation and perilobular, centrilobular, and periportal fibrosis. Mild
hepatocellular swelling and vacuolization along with areas of mild mononuclear inflammation
may also be observed but megalocytosis is uncommon. The extent of fibrosis is of clinical
importance because proliferating fibrous tissue gradually constricts the functional parenchyma. If
fibrosis is limited to centrilobular regions and “bridging” fibrosis, extending from the
centrolobular to periportal regions, is absent, the prognosis is usually favourable and horses can
fully recover from clover toxicity. In contrast, with ragwort toxicity fibrosis is typically much
more extensive and megalocytosis is a characteristic histopathological finding. Thus, it should
not be surprising that the prognosis for chronic ragwort toxicity is generally guarded to poor with
humane euthanasia required for most affected horses.
Hypertriglyceridemia, hyperlipaemia, and hepatic lipidosis: Hypertriglyceridemia, hyperlipemia,
and hepatic lipidosis develop consequent to mobilization of fat reserves to provide energy during
periods of negative energy balance. Thus, these metabolic alterations are secondary problems but
they must be addressed because they represent a serious complication that can significantly
worsen the prognosis of the underlying primary disease. Certain equine breeds, notably donkeys,
burros, and miniature horses, and overweight and pregnant horses are more predisposed than lean
animals. In addition to specific treatment of the primary disease process, appropriate nutritional
support in the form of a carbohydrate substrate is required to enhance metabolism of triglycerides
and reverse these metabolic alterations.
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