Nutrition for Maximum Performance
By Eleanor Richards
Copyright © 2013
The equine digestive system is like a disassembly plant. It takes water and feed (forage, concentrates and supplements) and breaks them down into a form the body can utilize.
There are two methods of processing: mechanical and chemical. The organs that make up the digestive tract do the processing.
Mechanical processing starts in the horse’s mouth as he uses his lips to sort and choose the desired feed. While grazing he will use his incisor teeth to bite off the grass. The tongue then moves the material back to the molar teeth where it is chewed and swallowed. The stomach continues to break down food with a churning action.
Chemical processing is present through out the digestive tract. It starts with the saliva in the horse’s mouth and ends in the large intestine. Bacteria, enzymes, and other substances are used to release the nutrients needed by the horse.
Horses are non-ruminant herbivores – they eat plants, but do not have a rumen. Animals with a rumen (cows, sheep, and goats) swallow the feed directly into a fermentation vat, the rumen, where it is broken down by bacteria. It is then regurgitated and chewed again before being re-swallowed. But, horses are hindgut fermenters. The feed a horse eats goes through the chemical and enzyme process before it is fermented in the hindgut. Horses do not chew a cud.
Notice, in the diagrams below, the horse’s meal enters the stomach; while the cow’s meal enters the rumen. Also notice how large the equine cecum is when compared to the equine stomach.
THE EQUINE DIGESTIVE SYSTEM
THE BOVINE DIGESTIVE SYSTEM
The best way to learn about the equine digestive system is to follow a meal, as it is broke down and processed. Please refer to the equine digestive system diagram as you follow the path.
Equine lips are very sensitive. Any horse owner who has tried to add medication, dewormer or a non-palatable supplement to grain can attest to the dexterity of the upper equine lip. This “prehensile” ability allows horses to grasp the most succulent grass. It also aids them in the ability to open stall latches, untie ropes and perform other feats of amazement.
Once the horse has gathered the food into his mouth he begins to chew. The chewing action stimulates three pairs of salivary glands – (1) the parotid, (2) the sublingual and (3) the submaxillary/mandibullar. A horse will produce 5 to 10 gallons of saliva per day.
If a horse does not get enough chew-time the feed is not moistened sufficiently. Senior horses or horses that bolt their feed can have problems with the feed causing an obstruction in the esophagus (choke).
Saliva also helps buffer the acids in the stomach. This helps protect horses from getting ulcers. The more forage a horse receives, the more saliva produced and the more buffering within the stomach.
The teeth are very important to the health of the horse. Many nutrition problems start here, so an understanding of the healthy equine mouth is important.
By the time a foal is a week old he will have 4 incisor teeth – 2 on the top and 2 on the bottom, these will be in the center. In another week the second set of incisors will come in and by 6 months of age the corner incisors will be in. Also, the pre-molars will be coming in at about the age of 2 weeks. There will be 6 pre-molars top and bottom. So, by the time the foal is 6 months of age he will have all his baby teeth, a total of 24 teeth.
The baby teeth, or caps, will start to shed by the age of 2 ½ years. The erupting permanent teeth will shove the caps out of the way. You may find them in the feed box. There are times when the caps will not be pushed out and this can lead to problems. An equine dentist or veterinarian will need to remove the cap, so the permanent tooth will come in properly.
Most adult mares will have 36 teeth and males can have 38 to 40. The extra teeth males have are called canine teeth. Mares do not usually get them and if they do they will be very small. Canine teeth will not erupt until 4 to 5 years of age.
A type of tooth that may cause problems is a wolf tooth. They are found in front of the molars. Wolf teeth do not serve any purpose. They may interfere with the bit. Many equine dentists and veterinarians re-commend they be removed. They have short roots and are easily extracted. Wolf teeth usually erupt between the age of 12 and 18 months.
The upper jaw is wider than the lower jaw and at rest the back teeth do not meet. As a horse chews his lower jaw moves side to side and this action causes the teeth to grind together. This grinding action causes the teeth to wear away. Below the surface of the gum-line is almost 4 inches of tooth, which erupts continuously as the exposed surface wears away. So, by the time a horse is in his twenties the amount of tooth left to erupt is a lot less than a horse that is 4 years old.
In this diagram of a fairly young but mature horse, notice how much tooth is below the gum-line.
Routine dental examination is important to how well a horse will utilize his feed. If all works well the teeth will wear away evenly, but that is rarely the case. Malocclusion, a term used to describe when teeth do not meet properly, can occur.
Overtime, points (sharp edges) can develop on the inside of the lower teeth and the outside of the upper teeth. These sharp edges inhibit the side-to-side movement of the lower jaw and soon the horse has lost the full range of the chewing action. These points are also very sharp and can lacerate the inside of the mouth and side of the tongue. Horses will pack material between the teeth and cheek to try to pad the sore area. An equine dentist or veterinarian will “float” or file off these points. This procedure does not hurt, because the adult equine tooth does not have nerves or blood supply.
A missing tooth can also cause problems. The corresponding tooth continues to erupt, but is not being wore off. Soon it is sticking above the rest of the arcade of teeth and the horse cannot chew properly. This tooth will need to be filed on a regular basis to prevent malocclusion.
The type of feed the horse eats will also affect the wear of his teeth. A horse that has a diet of only pellets or complete feed without any long stem fiber will have uneven wear of teeth. A horse that eats this type of diet or only hay will also develop long incisors. Because he is not nipping grass off with his incisors they can become long, which prevents the molars from grinding the feed properly.
Malocclusion can also be a genetic problem. Horses with inherited tooth problems will need to be monitored regularly and offered feed they can utilize.
Once the food has been chewed and softened with saliva the horse swallows.
The esophagus is a muscular tube that leads to the stomach. The length is about 50 inches for an average sized horse. It lies along the left side of the neck, just below the trachea (windpipe).
Choke, an obstruction of the esophagus, is a feed related concern. A horse that bolts (eats feed too quickly) his grain or does not have enough saliva to soften the feed can get the dry material stuck in his esophagus. Also, a horse that has tried to swallow a corncob or other large object can develop this problem. As the horse continues to eat the feed cannot pass by the obstruction and the material builds up in the esophageal tube.
The symptoms of a horse choking are frequent attempts to swallow, stretching out of the neck, excessive salivation, and feed material mixed with saliva coming out of the nose. A veterinarian should be called immediately as severe damage to the esophagus can result. Unlike humans, horses can still breathe while choking, but immediate care is still needed.
Choke can be avoided. A horse that bolts his feed should have several large rocks placed in his feeder. He will need to move them around to eat his ration. A horse that has an inflamed esophagus or does not have enough moisture to break down the feed should be provided with a feed that can be pre-soaked. This will aid in the passage of the feed to the stomach. Soaking the feed should also be done for seniors or horses that have tooth problems which result in them not being able to chew properly. Avoid feeding horses large pieces of apples, carrots, cubes, and treats.
A unique feature of the equine esophagus is the very strong cardiac sphincter valve. This valve is located where the esophagus joins the stomach and prevents food from being regurgitated. It also prevents horses from burping. The horse’s stomach will usually rupture before this valve allows the material to be regurgitated. This results in death and is why feed must be of the quality and quantity the horse can handle.
The stomach of the horse is very small in relationship to the size of the horse. It only makes up 8-10% of the capacity of the digestive system. The average horse’s stomach will only hold about 2 - 4 gallons and is about the size of a football. The stomach breaks food down mechanically and chemically.
The equine stomach is divided into two basic sections: the saccus cecus (nonglandular squamous mucosa) and a glandular section. There is a distinct ridge which divides them called the margo plicatus.
The nonglandular section is not protected from acid produced by the lower glandular section. This area is prone to ulcers. The pH level in the saccus cecus is approximately six (6) to seven (7).
Within the glandular section are two acid production regions – the fundic region and the pyloric region. This area is protected from acid by a mucous membrane.
The fundic section produces pepsin enzymes, gastric lipase enzymes, and hydrochloric acid which break down feed. Most of the digestion takes place in the fundic section. Pepsin breaks down protein into amino acids, which can then be utilized by the horse. The feed is also mixed with hydrochloric acid and bacteria that produces lactic acid. The pH level in the fundic sections is approximately five (5).
The pyloric section produces a small amount of enzymes and mucus. The pH level in this section is about two (2) – it is highly acidic.
The stomach does not break down fiber, so very little forage is digested in the stomach.
But fiber/forage is still needed to buffer the acids within the stomach. Forage also keeps the acids within the glandular section from “sloshing” up into the unprotected nonglandular section during exercise.
The muscles in the stomach uses rhythmic contractions called peristalsis. This mechanical action helps break down feed into smaller particles.
The design of the equine stomach is such that a horse needs small frequent meals. It fills quickly and empties quickly. Feed usually only remains in the stomach for about 20 minutes. Ulcers can result if the stomach is allowed to become empty.
Feeding a horse too much grain at one feeding causes the excess to be pushed into the small intestine before the digestive juices have a chance to break it down. Colic will be the result.
The pyloric sphincter is located where the stomach joins the small intestine. Once the meal is broken down the valve relaxes and the feed passes through to the small intestine.
The small intestine is a tube that measures about 50 - 70 feet in an average sized horse. Its capacity is approximately 15 gallons. Most of the nutrients from the grain portion of the diet are absorbed in the small intestine.
The breakdown of these nutrients relies on chemicals secreted by the pancreas, liver, and intestinal mucosa. Pancreatic enzymes help digest the feed. Because the horse has no gallbladder, bile is constantly flowing in from the liver. Bile breaks down fat. The available nutrients are then absorbed through the walls of the intestines.
Feed passes very quickly through the small intestine. In as little as an hour some types of feed will have moved through. However, it usually takes up to 8 hours for most of the feed to reach the end of the small intestine. It is very important to the health of the horse that soluble carbohydrates are absorbed in the small intestine. If they reach the large intestine fermentation can occur which will result in gas and colic. To avoid overloading the small intestine small frequent meals are strongly recommended.
Starch, complex sugars, protein from the grain portion of the diet, fat, fat-soluble vitamins (A, D, and E), and most minerals are absorbed in the small intestine. Protein from roughage, fiber, and phosphorus is not digested well in the small intestine.
The small intestine consists of three sections: the duodenum, the jejunum, and the ileum.
The duodenum prepares the food for absorption by mixing it with enzymes and chemicals. Very little of the nutrients are utilized here.
The jejunum is the longest portion of the small intestine. Most of the nutrients from the grain part of the diet are absorbed in the jejunum. Lining the inside of the intestinal wall are tiny projections called villi. The villi absorb the nutrients, which are now molecules and allow them to be utilized by the horse.
The ileum is the last section of the small intestine. The absorption of water and water-soluble vitamins takes place here.
The insoluble carbohydrates (fiber), any starch, or other material that was not utilized in the small intestine now moves on to the large intestine.
The large intestine is 25 to 30 feet long in an average sized horse. It has the largest capacity of the equine digestive system at approximately 30 gallons. Feed will remain in the large intestine for about 48 to 65 hours.
(Notice the large intestine is shorter in length than the small intestine, but holds twice as much.)
Digestion of insoluble carbohydrates takes place in the large intestine. Protein from the fiber portion of the diet is utilized. Phosphorus is absorbed. Any starch that was not digested in the small intestine will be worked on by microbes – which can cause gas and colic. Some B vitamins and vitamin K will be synthesized in the large intestine. (Definition of synthesis: the combining of parts to form a whole.)
There are five sections that make up the large intestine: the cecum, the large colon (which consists of the right and left ventral colon, pelvic flexure; and the right and left dorsal colon), the transverse colon, the descending colon (small colon), and the rectum.]
The cecum is a fermentation vat. It has been described as a comma shaped organ. The cecum is about 4 feet in length and has a normal capacity of approximately 8 gallons. The size can vary according to the quality of roughage being fed to the horse. The entrance and exit openings are both located at the top of the cecum. This can cause problems resulting in colic if the organ becomes compacted with non-digested material. Most feed remains in the cecum for about 7 hours.
The cecum is located on the right side of the horse. It is in a similar location as our appendix. Though, while our appendix can be removed, the horse needs his cecum. (Caecum is the United Kingdom spelling.)
Within the cecum are microbes that aid in the digestion of cellulose, fiber, and any remaining soluble carbohydrates. These microbes are somewhat specific as to what they digest. If a drastic feed change occurs the balance of the bacteria and protozoa is disrupted and colic can result. Any change of feed (concentrates or forage) must be made over a period of about 3 weeks, so the microbe population can adjust.
A horse that has a hay belly is the result of an expanded cecum. Poor quality fiber has accumulated in the cecum and can remain there for up to 72 hours. Switching to less mature hay will be more beneficial to the horse and prevent a hay belly from developing.
For more information about the cecum please go to: http://www.thewayofhorses.com/08_11_cecum.html
The cecum then leads to the large colon. The opening leading from the cecum to the large colon is about a 3-4 cm hole. It is a prime spot for blockages to occur.
Click Here to listen to the sounds of a healthy equine hindgut.
The large colon is approximately 10-12 feet long and is shaped like a horseshoe. Microbial digestion continues in the large colon. Any remaining vitamins, fatty acids, and water are absorbed. The large colon holds about 20 gallons of material.
The large colon is made up of 5 segments (listed in the order in which the feed travels): the right ventral colon, the left ventral colon, the pelvic flexure, the left dorsal colon, and the right dorsal colon. The large colon folds back on itself several times and is held in place by the bulk, which it contains. At several points the colon narrows and blockages can occur in these narrow passageways.
The design of the large intestine requires plenty of good quality forage be available to the horse. If the colon becomes empty the chances of it becoming twisted increases.
The remaining material then travels through the transverse colon and into the descending colon (small colon). The transverse colon is a very narrow tube and another primary spot for blockages.
The descending colon uses contractions (peristalsis) which results in fecal balls forming. Any remaining moisture is also extracted in the small colon. It measures about 12 feet long and is very narrow at about 3-4 inches in diameter. It holds about 5 gallons of material. The small colon is also free to move and can become twisted.
The descending colon then leads to the rectum. The rectum is a short straight tube and acts as a storage area for the fecal balls until the horse expels them.
Click here for more pictures of the equine digestive system. The file is large so it may take time to load if you have a slow internet connection or dial-up. Please email me if it will not load for you and I'll try to send it another way.
1. At what age should a dental exam or care begin? Feel free to do outside research – you may ask your vet.
2. How often should horses have their teeth examined?
3. Follow the steps outlined below and send a report of your findings to your instructor. (Contact information would be provided for the active student.) If you have a recent exam performed by a specialist you may send it along with your report, but still complete and submit your own findings.
When writing your report please check grammar, spelling and use proper formatting of your paper. Please do not send it in all caps and make sure you use paragraphs. Most important – please include your full name and correct email address.
1. Watch your horse eat. Notice if he drops grain or tilts his head to the side while chewing or if he dunks his hay in the water. These are all signs of potential problems.
2. While standing in front of your horse - be careful he doesn't throw his head and hit you with the end of his nose....place your fingers on either side of his cheek about where his back teeth start. Gently feel along the side of his jaw. See of you can feel the top row and the bottom row. Go down the top row...gently palpating...notice if he seems sore when you touch a certain area. Then do the same along the bottom row.
3. Lift his lips and check his front and side teeth. Notice any chips and how they are aligned. If he won't let you lift his lips to look at his front and side teeth you need to practice. Notice if the gums are pink and healthy.
If you detect any problems you'll need to call a vet or equine dentist. This is not a thorough exam, but it can help you decide if a more intense exam is needed. Every horse should have their teeth examined at least once a year by someone who can check the back ones - those are the teeth that develop points, which can lead to chewing problems and utilization of feed.
Click Here to take the Quiz This would be a link to the quiz for the active student.
To enroll in the Associate in Arts course: Equine Nutrition for Maximum Performance Click Here