The gastrointestinal tract of a horse is a complicated structure that works efficiently when fed appropriately for its evolutionary design. Understanding some key elements can help you feed a safe diet.
Once food is chewed, mixed with saliva and swallowed, it enters the stomach. Digestive enzymes break down food material and move it on to 70 feet of small intestines. While food is processed—for up to eight hours—in this section of bowel, protein, carbohydrates and fat are absorbed into the bloodstream. From there, the ingesta moves into the cecum, where microbes further ferment fiber into volatile fatty acids to provide energy, while cecal microbes produce vitamins K and B.
From the cecum, ingesta moves into the large colon, the primary site of fluid absorption. It takes a couple of days for material to pass through the many bends and folds of the large colon. The material then transits to the small colon and on into the rectum. Remaining undigestible material passes as manure.
The key to intestinal health is for a horse to consume a diet predominantly of high-quality fiber. Problems arise when too much starch (from cereal grains) enters the small intestines and spills over into the cecum and colon. This causes acidification of the bowel contents leading to death of good microbes important to digestion and equine health. Overgrowth of undesirable microbes has wide-ranging effects on intestinal health, and aberrant starch and sugar metabolism in the colon and cecum can lead to colic and laminitis.
Work with your equine veterinarian or an equine nutritionist to balance your horse's diet, focusing on quality forage of the right type(s) as the basis of any equine diet. Then focus on meeting the nutritional needs of your horse based on its individual requirements and use.