Digestion and absorption
Zebras and other equids have a single stomach and a kind of digestion called hind-gut fermentation which allows them to digest and convert large amounts of plant material during a twenty hour period. Food passes quickly through the gut, so only the most readily digestible portions of the food are used the rest is excreted. Zebras, wild horses and asses eat 12-16 hours a day and are not selective in what they eat. With a small, simple stomach and large fiber-digesting hind gut, equids are designed to eat small portions throughout the day.
1. Esophagus
2. Stomach
3. Small Intestine
4. Cecum (large intestine)
5. Colon (large intestine)
6. Rectum
1. Digestion starts with the mouth;
mechanical digestion.The tongue moves food to the back of the mouth to the pharynx or throat where it enters the esophagus and is swept down with rhythmic contractions of smooth muscles this is called peristaltic waves.
2. The equid stomach is small. When food reaches it digestive juices (acids and enzymes) are secreted and the mixture starts to be broken down. Very little is absorbed in the stomach. Proteins and carbohydrates are only partially digested and fats are slightly hydrolyzed, broken down by reaction with water, before the food passes into the intestine.
3. In the small intestine protein splitting enzymes reduce protein to amino acids which can be absorbed in the colon. Portions of the food, including vitamins and minerals, are digested here and absorbed into the blood.
4. Hay, grass stems and other fibrous roughage are passed on to the cecum. The cecum is the first part of the colon and serves as a fermentation vat where billions of bacteria and protozoa produce enzymes that break down plant fiber. Fermentative bacteria and protozoa support one another in a complex food web inside the equid where waste products of some species serve as nutrients for other species. The plant fiber is converted into volatile fatty acids which are eventually absorbed and passed to the liver. Here they are converted into glucose, a sugar, which can be used immediately or stored for use later.
5. The remaining substance is passed from the cecum into the next part of the large colon. Microbial digestion continues in the large colon and nutrients are absorbed here. Material from the large colon enter the small colon where the majority of water in the horse's diet is absorbed.
6. The rectum is where waste is formed into balls of dung and acts as a holding chamber. Eventually the waste is passed out through the anus. In hind gut fermentors the fermentation process occurs in an areas where bacteria and protozoa can not easily be used as a nutrition source. As a result they miss out on all of the nutrients in these microorganisms. This is not the case with ruminants.