South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
The list of medical problems that can present with a complaint of weight loss is extensive (Figure
2). For the remainder of this presentation, the discussion will be limited to gastrointestinal
disorders that may cause weight loss and/or ill thrift.
Figure 2. Causes of weight loss in 60
horses presented to the internal medicine
service of an equine hospital in France,
from Tamzali Y: Chronic weight loss
syndrome in the horse: a 60 case
retrospective study. Equine Vet Educ
18:289-296, 2006.
Lawsonia intracellularis: Lawsonia intracellularis infection causes a syndrome of ill thrift and
weight loss (without obvious diarrhoea) that has been coined “equine proliferative enteropathy”
(EPE). EPE has emerged as an important disease of foals through yearlings. Lawsonia
intracellularis has long been known to cause proliferative enteropathy in pigs. In both species, the
organism is typically found in the apical cytoplasm of intestinal crypt cells. Infection results in
crypt cell expansion and elongation that manifests grossly as hyperplasia and thickening of the
distal half of the small intestine. Inflammatory cells and goblet cells are reduced or absent but
lack of a functional brush border leads to malabsorption and weight loss. Faecal shedding occurs
as infected epithelial cells are sloughed into the intestinal lumen. With pigs the disease spreads
through comingling of carrier animals with naïve pigs but in horses the source of infection and
means of transmission remains unclear (although a faecal-oral route is probable). EPE commonly
affects only a few individuals in the herd although larger outbreaks have been described.
Affected young horses are usually not recognized until they have been infected for one or more
weeks. Although they may have mild diarrhoea, this is not a consistent finding and the most
common presenting complaints are weight loss with a dull attitude (ill thrift). Characteristic
findings include marked hypoproteinemia (<4.0 g/dL [40 g/L]) in combination with thickened
small intestinal walls (wall thickness often >10 mm; normal is <3 mm) detected on abdominal
ultrasonography (Figure 3). In addition, more careful palpation of the sternum and lower
abdomen often reveals mild to moderate ventral oedema. In fact, these findings are nearly
pathognomonic for EPE in a weanling or yearling.
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