Last updated on March 11th, 2023 at 07:29 am
Unlike cows, the horse digestive system is non-ruminant, which means that horses do not have multi-compartmented stomachs like cattle do. Rather, horse’s have a simple stomach which works more like a human’s. They are also herbivores, which means that they live on a diet of plant-based material. Now let’s take an in depth look at the entire equine digestive system.
Table of Contents
Horse Digestive System Diagram Labeled
Let’s first look at the horse digestive system labeled diagram below to get a better understanding.
The horse digestive tract starts with it’s mouth. Horses use their lips, teeth, and touch to grasp and chew their food. It has tactile lips that help when feeding.
In the mouth, the horse mixes food with saliva to create moist boluses that it can swallow with ease. The horse has three glands for the production of saliva that include sublingual, sub-maxillary, and parotid. Its saliva has bicarbonate that becomes a buffer to protect the delicate amino acids from being damaged from a highly acidic stomach. The saliva has small amounts of amylase enzyme that assists in digesting carbohydrates.
Male horses have 40 teeth, while females have 36 teeth. There are some horses with wolf teeth. Their upper jaw is a little wider than the bottom jaw to allow for complex chewing. Horse chewing involves vertical, backward, and forward motions. This enables the horse to mix the feed with saliva and start digesting.
Depending on the size of the horse, it can masticate its feed in a few or many jaw sweeps. A horse weighing 500kg may take 3400 sweeps and 40 minutes to chew a kilo of dry hay. Other ponies may need twice the time and effort to digest the same amount. Besides, a mature horse will take 850 swipes in ten minutes to take a kilo of oats. Ponies may take up five times the period.
Chewing pasture requires a long jaw sweep. This enables uniform wearing of teeth. However, with regular feed composed of grains, the chewing action is shorter and often leads to sharp edges and hooks. Such teeth require rasping or ‘floating’ to maintain appetite, chewing efficiency, and temperament. Besides, proper feeding reduces the risk of choking.
The esophagus is a long tube that connects the stomach to the mouth. Unfortunately, horses have a very long esophagus that lowers their reflux capacity. This means that food that has not been chewed correctly can lodge in the esophagus and choke the animal. That is why owners are advised to take care of their horse’s teeth so that these animals can chew food correctly. It also prevents a case where a horse bolts down half-chewed food down their esophagus. You can also add some chaff into the feed bin to slow down the feed rate and thereby lower the chances that the horse will choke.
Surprisingly, horses have a small stomach when compared to their overall size. Besides, it only takes 10% of the entire digestive system. Generally, horses are mean to eat little portions of roughage every while. However, with domestication, this is not what happens. Most owners feed horses with two large meals, mostly grains, each day. This negatively affects the horse’s health and digestion. Animal husbandry experts advise small feeds several times during the day. Unfortunately, this tends to increase the costs of managing the animal.
The stomach has a pepsin enzyme, which helps break down proteins. It also has hydrochloric acid that helps break food particles. Food stays in the stomach for a little while (can be 15 minutes) if the horse is regularly eating. However, if it has stayed long without feeding, food may remain for up to 24 hours.
Many farmers are torn between choosing whether to feed horses with hay or grain, as their first meal. Grains stay in the digestive system much longer due to the density. However, there are no advantages of feeding the horses with feeds first. If your horse is a fast feeder, consider adding chaff to the feed to slow down feed consumption. Besides, most farmers are not sure whether to give water before or after feeds. However, it is best that you provided some clean water at all times and let the horse take some when it feels the thirst.
When changing the feeding cycle, you may leave the horse without food in its stomach for extended periods. However, when on an empty stomach, the hydrochloric acid destroys the saccus caecus section of the stomach and damages the squamous cells that are not protected. This may cause ulcers in the stomach. According to research, over 80% of all the thoroughbreds have had stomach ulcers at some point. However, if you increase the amount of roughage in the feed, allow horses to graze and give small but frequent meals, you will reduce the severity of these ulcers and prevent them from occurring regularly.
Equine Small Intestine
Digested food moves from the stomach and gets into the small intestine for further digestion. This section of the digestive system has three different sections, namely: jejunum, duodenum and ileum. Apart from pepsin that breaks down proteins, little other digestion happens in the stomach, leaving much digestion to occur in the small intestine. There are a few enzymes found in the intestines as the pancreas secretes most of them.
After the digestion process, nutrients from the food are absorbed into the blood via the intestinal walls. The blood then nourishes cells with the nutrients. About 30% to 60% of all the carbohydrates are digested and absorbed in the small intestine. All amino acids also get absorbed in the same place. Other nutrients that are absorbed in the small intestine include vitamins, D, A, K, and E. Horses also get their phosphorus and calcium via the small intestine. When you change the structure of the carbohydrates through processing technologies as micronization, you can increase the digestion and subsequent absorption to 90%. This helps take the burden from your small intestines by preventing a digestive system overload and avoiding problems such as acidosis, colic, and laminitis.
Digesta takes half an hour to an hour in a horse’s small intestine, with food moving at around 30 cm every minute. However, the process can take up to three hours. Unfortunately, if the food goes down quickly, there is little time for enzymes to break down the feed completely, and this leads to loss of nutrients. You can add some oil in the feeds to lower the flow rate of the feeds in this section. This is vital in enhancing the horse’s digestive efficiency and fully breaking down proteins, carbs, and fats. Besides, most of the nutrients are absorbed into the blood.
If there are toxic matter in your feed, your horse cold die from colic. Horses are unlike cattle whose digestive system contains bacteria that remove toxins before the feed reaches the small intestine. In the case of horses, toxins get into the small intestine and absorbed into the blood with fatal results. Therefore, desist from giving stale or moldy feeds to your horses. Most farmers feed their cattle with urea that utilizes into protein in their rumen section of the stomach. Unfortunately, if fed to horses, it gets absorbed into the bloodstream before reaching the cecum where it can be utilized. This makes urea toxic to horses. However, most horses can tolerate the urea amounts in most cattle feeds.
There is some amount of microbial protein that is made in the large intestines. However, horses are not able to utilize the proteins. Animals that require lots of proteins such as lactating mares or foals along with regularly exercising horses need high-quality protein for ease of breaking down and absorption in the small intestine. Practically, you do not have to increase the crude protein intake but the quality of the proteins you give to your horse. Ensure that the horse gets the right levels of threonine, lysine, and methionine as per its needs.
The large intestine is also called the hind gut. It has several sections that include the ascending or large colon, caecum, small colon, anus, and rectum. This is the section where digestion is completed. However, unlike the small intestine, much of the digestion in this section is done by microbes rather than enzymes. Millions of symbiotic microbes live in this section and effectively break down undigested starches and plant fibers into volatile fatty acids. These small compounds are then absorbed into the horse’s bloodstream through the colon wall.
Unfortunately, unlike other ruminants, the horse’s digestive tract is not best placed to digest lots of crude fiber, low levels of carbs, and low-grade proteins in their feeds.
The caecum looks like a sack. It is about 1.2 meters in length and can hold between 28 liters to 36 liters of fluid and feeds. It is a microbial inoculation chamber, just like the cow’s rumen. These microbes break down all the feed that was not digested in the small intestines. It also works on roughages such as pasture and hay.
This part of the hindgut has a unique structure, as both the entrance and exit are located at the top. Feed enters from the top, mixes with the microbes, and the matter that is left after digestion gets expelled back to the top. This may lead to a problem if your horse eats lots of feed without adequate hydration or makes a rapid change in its diet. Both of these scenarios cause the food to be stuck at the bottom of this part. This then develops into pain in a condition called colic. The population of microbes in caecum digests specific feeds. It may take up to three weeks for the bacteria to adjust to new diets and work optimally. This is why animal husbandry experts ask you to introduce new diets throughout one to two weeks.
Feeds stay in the horse’s caecum for about seven hours. During the time, it is broken down and fermented. At the end of the process, microbes will have produced proteins, Vitamin B-complex, and K, along with fatty acids. The fatty acids and vitamins get absorbed through the wall into the bloodstream. However, little proteins get absorbed.
Horse Large Colon
There are three sections of the large colon: the dorsal colon, left, and right ventral colons. The process of microbial digestion continues in this section. Nutrients such as vitamin B trace minerals, phosphorus, and some fatty acids get absorbed in this section. Ventral colons have a distinctive sacculated structure that resembles a set of pouches. This design allows it to digest large amounts of fibrous feeds at once. However, it may also increase the risk of colic. They can also be twisted with ease and fill with gas. The feed stays in these pouches for a period of between 7 and 65 hours.
Equine Small Colon, Anus, and Rectum
The small colon is as long as the large colon. However, it has a lumen of just 10 cm in diameter. By the time feeds reach this section, much of the nutrients have been extracted from the feeds, and the matter left on the digestive tract does not have any nutritional value. Therefore, the small colon does not digest the food but rather absorbs excess moisture back to the body. The moisture extraction process results in the formation of fecal balls. The balls are made of undigested matter, and indigestible feeds that the horse ate between 36 and 72 hours before. They pass through to the rectum for expulsion via the anus.
Horse GI Anatomy
Each of the above in the horse GI anatomy functions well in the normal conditions when all factors are held constant. However, the equine GI tract is quite sensitive and can be upset by a few issues. Colic is the leading cause of death for horses.
A sudden change in the type of feed you give to your horse may lead to a change in the large intestine’s bacteria population. This may result in problems such as colic or reduced digestive efficiency of the colon. Besides, it is hard for microbes to keep working efficiently if your horse is stressed-up, suffering from an injury or illness, received a dose of antibiotics, or traveled long distances. Other conditions that have adverse effects on microbes include high-performance horses feeding in lots of grains or a weaned foal. Therefore, you should always be on the lookout for the problems in the hindgut and keep track of what you are feeding your horse.
The rule of the thumb is to feed the horse as close to the grazing habit as possible. Besides, feeding the horse with small amounts regularly can help reduce incidences of digestive tract problems. Proper feeding enables you to enjoy the full potential of your horse.
It is important to note that a horse is an herbivore, but it is non-ruminant. This is because it does not have various compartments like other herbivores such as cattle. As previously mentioned, their simple stomach functions like the human one. The equine digestive system is unique in that it uses enzymes to digest feed first in its foregut and then ferments the rest of the food in its hindgut.