When horses can’t have fresh pasture, either because of stall confinement or the season, the logical next best thing is hay. After all, hay is just dried grass. All the major nutrients – fiber, protein, carbohydrate – are basically the same with one important exception. Water.
Hay averages around 10% water while grass is at least 70%. Pasture is not only a high moisture food, the water is delivered at the same time as the nutrients requiring digestion. Water is arguably the most important but overlooked component of digestive tract function. Adequate intake is required for:
- production of saliva, pancreatic juices, bile and other secretions into the GI tract
- function of digestive enzymes
- absorption of digested food
- fermentation of fiber in the hind gut
- smooth passage of food through the digestive tract
When horses are on pasture they get so much water from grass that they may drink very little water, or none at all. The move to a hay based diet is a huge change. Water intake is partially driven by how dry the diet is but there is also an important hormonal component.
Thirst is regulated in the brain by cells which “read” the sodium concentration of the blood. If water is low, sodium concentration rises. The first adaptation is to decrease urine production and make it more concentrated. Water also moves from the tissues and intestinal tract into the blood. This is the beginning of disrupted intestinal function. If sodium level continues to rise, the horse will be triggered to drink and restore normal hydration. If it doesn’t, he will stay in this state of blood levels OK but tissues and gut dehydrated.
Guaranteeing adequate salt (sodium chloride) intake protects against dehydration. Your horse needs salt, even in winter, because sodium is lost in the manure and urine every day. If salt intake is too low, the horse will stay in a constant state where tissues and intestinal contents are dehydrated to keep blood salt and water levels normal (above). When salt intake is normalized, blood concentration rises quicker and the horse is triggered to drink.
You can also support digestive health by feeding a probiotic supplement which also has high digestive enzyme activity. This helps ensure that protein, fat and simple carbohydrates get digested where they should, in the small intestine, while fiber passes back to the hind gut.
Feeding an additional soluble fiber source, like psyllium husk, also greatly supports the hind gut. This should be fed after fully hydrating it with water. The fiber will carry water to the hind gut contents and also serves as a prebiotic, enhancing growth of fiber fermenting organisms.
Finally, make sure the horse has access to water that will not freeze over. Better yet, slightly warmed water encourages intake. You cannot rely on the horse eating enough snow to support good gut function.
Cold weather and dry diets pose some challenges to good digestive health but understanding the issues, and the relatively simple fixes, will help you keep your horse’s GI tract functioning well.
Eleanor Kellon, VMD