A horse’s digestive system is an important part of its physiology, because it allows the animal to digest and absorb food. The gastrointestinal tract includes the stomach, duodenum, jejunum, ileum, cecum and colon. A healthy digestive system is essential for good health and performance in horses.
The digestive process in the horse begins with a horse chewing its feed, and includes prehension (incisors grasp the feed) and mastication (molars grind the feed). Chewing breaks down large pieces of food into smaller ones that can be more easily absorbed by the body. The ingested food then passes through the stomach, where a sphincter prevents the horse from vomiting. The stomach has a greater and lesser curvature, and the space between the greater and lesser curvature is called the omental bursa.
Next comes the ileum, which enters the cecum via the ileocecal orifice. The ileum is thicker than the duodenum and jejunum, and has prominent bands and sacculations. The ileum is also prone to intussception, a condition where one segment of the intestine gets caught inside another section. Horses with intussception may exhibit a distended abdomen, a swollen belly button and a painful nasogastric tube.
The larger diameter ileum is also prone to entrapment at the epiploic foramen. This is a small hole near the ileocecal orifice where the ileum enters the cecum. The entrapment causes abdominal pain and discomfort, and the ileal segment is then often excised surgically to relieve the obstruction.
After the ileum, the equine stomach has a nonglandular and glandular region. The nonglandular portion is lined with stratified squamous epithelium and can appear white on US images. The glandular region contains a layer of fat that can become hyperechoic. The proximal portion of the stomach has the margo plicatus, which can be seen as a rounded area on an image.
The equine stomach has a pylorus, which is the muscular structure that opens and closes the gastric sphincter. The pylorus is also the pyloric outlet, where bile flows from the liver to the stomach. The equine pylorus is much shorter and has less of an angle than the human pylorus, because the sphincter opening is closer to the cardia.