South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
A simpler test to perform in practice is the modified oral glucose tolerance test (Murphy et al
(1997) Vet Record 140 342-343). This involves collecting a resting sample and a second single
sample at 120 minutes, plus using a 20% rather than 15% cut-off value for total malabsorption.
Sensitivity and specificity are comparable with the conventional glucose tolerance test.
Transabdominal/transrectal ultrasonography
Both small and large intestinal wall thickness and motility should be assessed as well as the
volume and echogenicity of any free peritoneal fluid (see notes on equine abdominal ultrasound).
Gastroscopy and duodenoscopy
This is indicated in cases with diffuse intestinal disease and concurrent poor appetite/weight loss.
Gastric ulcers can occur secondary to reduced intake of roughage or with delayed gastric
emptying due to altered intestinal motility. Duodenoscopy allows collection of transendoscopic
duodenal mucosal biopsies, which can identify changes such as inflammatory infiltrate, villous
atrophy and neoplasia. Biopsies are likely to be small and superficial, which can limit diagnostic
use. Using a „double bite‟ technique can help produce deeper, more diagnostic samples.
Laparoscopy/exploratory laparotomy
Multiple full thickness intestinal biopsies obtained by laparoscopy (small intestine) or laparotomy
(small and large intestine) are more likely to identify intestinal pathology than either rectal or
duodenal biopsy, but are more invasive. In horses with significant hypoalbuminaemia, general
anaesthesia may be contra-indicated and wound healing will be delayed.
Specific causes of chronic diarrhoea and targeted therapy
Inflammatory bowel disease
IBD is a poorly defined disease of unknown aetiology. It is classified according to the type of
inflammatory infiltrate identified on histopathology. This may be lymphocytic-plasmacytic,
granulomatous, eosinophilic or mixed. Additional histopathological findings include villous
stunting, deformation or fusion.
Lymphocytic-plasmacytic enteritis (LPE) appears to be increasingly common (or better
recognised). Affected horses tend to present with weight loss, with or without diarrhoea, and/or
recurrent colic. LPE predominantly affects the small intestine, although can be diffuse throughout
the intestine. Early published data gave a poor prognosis for this form of IBD; more recent work
has suggested better survival rates.
Granulomatous enteritis is much less common and results in diffuse granulomatous lesions
throughout the small intestine, plus villous atrophy. Young horses are more commonly affected
and present with chronic and progressive weight loss and anorexia. Skin lesions involving the
head, limbs and coronary bands may also be present.
Eosinophilic enteritis can present with focal eosinophilic lesions (focal single or multiple plaques
or circumferential mural bands), as diffuse eosinophilic infiltration throughout the intestinal wall
or as the very rare chronic wasting multisystemic eosinophilic epitheliotrophic disease (MEED).
The latter form has a poor prognosis for survival, whereas the focal or diffuse forms carry much
better long term survival rates.
The mainstay of therapy for IBD is corticosteroids. Oral prednisolone (1-2mg/kg once daily) or
dexamethasone (0.05-0.1mg/kg) can be highly effective. Prolonged courses are often required, for
up to 6 or 12 months. The dose is usually gradually tapered according to response. Azathioprine
103