Lipid disorders in horses and foals

Disorders of lipid metabolism are characterised by an increase in levels of circulating lipids, specifically triglycerides, which occurs as a result of a negative energy balance. This negative energy balance arises from a mismatch between the body's needs (for example severe inflammation, gestation and lactation) and its intake (for example anorexia and gastric reflux). Stressors like transportation can precipitate this condition. The clinical signs of lipids disorders include inappetance and dullness, but might not be very specific. The excessive circulation of lipids can often be identified by the opalescence of the serum (Figure 1). While mild to moderate increases in circulating lipid concentrations may have relatively mild clinical consequences, severe increases can result in excessive fat deposition in the liver and the kidneys, impairing their function and often leading to serious complications and even death.

In horses, lipids are absorbed from the gastrointestinal tract in the form of fatty acids. Short-chain fatty acids bind to albumin and travel through the portal circulation, but most fatty acids undergo transformation into phospholipids and triglycerides in gastrointestinal epithelial cells (van der Kolk et al, 1995). They are then transported in the portal circulation or incorporated as chylomicrons and transported through the lymphatic circulation. Horses are hindgut fermenters, which gives them the ability to change from monogastric glucose-oriented metabolism to a ruminant fatty acid-oriented metabolism (Argenzio and Hintz, 1972; Naylor et al, 1980).