While the natural diet of grasses that horses would eat while grazing isn't particularly high in fat, these plants do contain some fat and horses digest and absorb it well. | Photo: iStock

A.Most vertebrate animals have a gallbladder, which is a small organ that stores and concentrates bile until it is released in to the digestive tract. Bile (sometimes referred to as gall) is a greenish-brown liquid made constantly by the liver. You’re correct: Horses don’t have gallbladders, and so there’s nowhere for them to store bile. Instead, the bile is transported by the biliary system directly to the small intestine.

Bile’s purpose is to help solubilize the products of dietary fat breakdown. This is a vital step in the digestion of dietary fats. Bile salts surround droplets of fat in the small intestine helping to form micelles (an aggregate of molecules in a colloidal solution, such as those formed by detergents). This prevents fat droplets from aggregating and increases the fat’s overall surface area, resulting in more area for lipase enzymes to work. The micelles then carry the products of fat breakdown into the cells that line the small intestine. Fat absorption is therefore increased due to the action of bile salts.

In essence bile works like dish detergent used for washing greasy plates. With only water, the fat and water repel each other, and it’s hard to remove the grease from the plate. However, if you add detergent to the water it emulsifies the fat such that it mixes more readily with water