The Digestive System
Horses have a huge digestive system but a stomach capacity of only about four gallons. In the wild, the horse grazes almost continually, passing food through its digestive tract all the time, emptying out the stomach and processing the food through to elimination. If you've ever cleaned out horse stalls on a regular basis, you're all too familiar with how much food comes out the other end in a day's time. The volume and consistency of manure can be a fairly reliable barometer of health. That's why it's important to become familiar with your horse's elimination habits and always be observant, so you'll notice right away if anything changes.
FIGURE 9.3: Digestive System of the Horse
To approximate natural conditions as closely as possible, domestic horses should ideally be kept on pasture all the time, or at least turned out to graze in a paddock for several hours a day. The horse's digestive system is a large, complex machine that needs to constantly process food but can't be stuffed too full. The horse without access to pasture relies on good management practices of his owner to feed him small amounts a few times a day. If the horse receives grain, it should be divided into at least two and perhaps three meals per day. The quantity depends on the level of work required of him. Hay can be fed free choice, but many people also split this up into three or four feedings a day.
Many things can go wrong in the horse's digestive tract. For one thing, the horse cannot vomit and rid herself of something that upsets her stomach. Because the horse evolved to graze with its neck bent down to eat, the muscles in the esophagus only work to move food in one direction. A one-way valve at the entrance to the stomach prevents the contents from moving backward.
Overall, the equine digestive system is poorly equipped to process the huge amounts of food needed by an animal its size, especially in the manner that domestic horses tend to be fed. It is also full of kinks and turns that increase the potential for blockage.
Smaller, frequent feedings are best; otherwise, the stomach will move food before it is fully digested. This can mean that the horse isn't getting the full nutritional value of its feed. A greater risk is that the food may become impacted at one of those odd kinks and turns in the system.
The small intestine is approximately seventy feet long and has approximately a twelve-gallon capacity. Some food is processed by the liver and stored as energy. The cecum is a critical apparatus that holds a huge amount of bacteria. The bacteria break down cellulose and produce fat-soluble vitamins that are absorbed and used.
The large colon is around twelve feet long. It holds as much as twenty gallons of semi-liquid stool. The small colon is a little shorter, at ten to twelve feet long. In it, water is absorbed and stool is formed into balls. The rectum, around a foot long in the horse, is the channel through which the stool leaves the body.