Equine digestive tract
A horse has the same requirements for energy, protein, vitamins and minerals as other animals but differs in the type and function of its digestive system. The digestive system of the horse falls somewhere between that of a ruminant and that of a non-ruminant. In terms of their diets, they are herbivore specialists who can only process one type of plant material efficiently. Too much, too little, or the wrong kind of foods can all cause digestive upsets that can lead to illness or fatality.
As with all animals, digestion starts in the mouth. Horses have evolved to efficiently crop grass with their fore teeth and grind it with their back teeth. A horse will have two sets of teeth. At about two to three years of age a young horse will loose its milk teeth. The adult teeth that then descend continue to grow throughout most of its life. There are specific patterns of tooth growth that make it possible to estimate how old a horse is.
Because horses can spend up to 95% of their time grazing close to the ground a fair amount of grit is ingested. This grit continually grinds down the horse’s teeth. In domestic horses tooth wear can be uneven or growth can exceed the amount of wear. This makes a yearly visit from an equine dentist a necessity to remove any excess growth or sharp edges that could form.
Horses hold their food at the back of the mouth before swallowing. Thoroughly mixed with saliva it is propelled down the esophagus by strong muscular contractions. Ideally there is enough saliva to help the food down but, a greedy eater who doesn’t chew its food completely and hasn’t enough saliva mixed with the ground up food can choke.
The food then travels to the horse’s stomach. Unlike cattle, that are ruminants with several stomachs, horses have only one stomach. Horse’s have small stomachs that function best if they are never quite full. A full stomach may feel satisfying to humans, but it can be very uncomfortable, and even harmful for a horse. Because the valve into the stomach only opens only one way, horses cannot regurgitate. If something is eaten to disrupt the digestives system there is only one direction it can go.
In the stomach the food is mixed with more acids and enzymes that help break it down. Food then travels into the small intestine where more secretions from the intestine and organs such as the liver and pancreas break it down into basic components; the nutrients and energy that the horse requires.
The Large Intestine
Once the food has traveled through the small intestine it enters the large intestine. This is where most of the water is extracted from the food and the fiber is broken down. The large intestine is also the location of the caecum, a section of intestine that can be filled with the ingested grit, causing sand colic. Because of the narrow bends within the intestinal system, impacted food can cause constipation and colic. Twisting or telescoping of the gut can occur, causing extreme pain. Unfortunately, even with today’s excellent veterinary care many horses that suffer from severe colic resulting in a twisted bowel must be euthanased.
From the large intestine faeces travels to the rectum and is expelled through the anus. The whole process of digestion can take up to 48 hours.
Horses can suffer digestive distress from toxic plants, stress, bacteria such as salmonella, parasites, over-eating, and swallowing foreign objects. Exposure to any of these elements can result in colic.
Colic is an indication of abdominal pain, and is not a condition in itself. Colic symptoms include: kicking or biting at the sides, elevated pulse, violent rolling on the ground, dull, listless or unusually irritated behavior, constipation, decreased gut sounds, sweating, and refusal to eat or drink. If your horse is exhibiting colic symptoms call your veterinarian immediately.
Maintaining a Healthy Gut
Keep your horse’s digestive system healthy by providing plenty of clean water, good quality hay or pasture and plenty of exercise. A regular de-worming program will help eliminate parasite damaging infestations and regular dental care will ensure that your horse is grinding his food efficiently.