Links to

Is It Fat
or Is It...
Hay Belly?

A "Hay Belly" is just a fat
horse that's fed too much
hay.........right?  Well, after
a lunch with Jeff Kiewatt
(Consumer/Equine Specialist),
I was totally confused.  According to Jeff, hay is digested between between the stomach and large intestine.   (Ever herd of the Cecum or the term "hindgut"?)  And, poor quality hay takes a whole lot of time to digest.  So, a hay belly is just that....undigested hay in the horses belly!

So, after more research We found this information on the Triple Crown Nutrition, Inc., site. (

"Basic Understanding of the Equine Digestive System

Digestion is the process where feedstuffs that the horse consumes is broken down and converted to its simplest form so nutrients can be absorbed into the bloodstream. These nutrients provide fats, carbohydrates, vitamins, minerals, and amino acids (protein) required for growth and maintenance, or they can be stored until needed later. The digestive process in the horse primarily involved enzymatic action and fermentation. For you to feed your horse to its full potential, a basic knowledge of the digestive system is important. This information is based on a typical 1000-pound horse, but would be accurate for horses of any size and breed from miniature horses up to the draft breeds. Only the size and capacities of the various parts would differ.

There are many different types of digestive systems used in animals. A horse is classified and a non-ruminate herbivore and differs substantially from both humans and ruminates, such as cattle. The digestive system uses both high levels of enzymatic action in the small intestine and high rates of microbial fermentation in the large intestine. A horse functions best by grazing, eating small amounts of roughage products over an extended period of time. In fact, research has shown that pastured horses will spend about 70% of their time eating. The other 30% will be spent sleeping and socializing.

The digestive tract starts at the mouth and continues through the pharynx, esophagus, stomach, small intestine, cecum, large colon, small colon and ends at the rectum. Associated organs that aid in the total digestive process are the salivary glands, liver, and pancreas. The total digestive tract length is about 100 feet long that abruptly changes in diameter and is lined by mucous membranes along the way mostly excreting digestive fluids. The digestive tract also requires movement by the horse to help the various muscles mix and move digestive tract material. Research has shown that stall bound horses without much freedom of movement are more prone to impaction colic.

The digestive process begins in the mouth where teeth reduce the particle size. The lips are extremely nimble and can select specific plants, small particles of feed, and sort stones and pebbles from what they graze and eat. The incisors sheer the plant stalk and the molars grind to the appropriate size. The chewing process stimulates the flow of saliva, which lubricates the feed prior to swallowing. Geriatric horses who have depressed saliva glands or horses who are aggressive eaters and often do not chew their food long enough are prone to choke. Steps such as wetting the feed or slowing down consumption need to be considered with these horses. If a horse does choke, the esophagus and trachea are two separate tubes down the throat, so suffocation is not an immediate threat. Do not allow the horse to eat or drink and a vet does need to be consulted to clear the choke to avoid any potential aspiration of other feed or liquid into the lungs.

Once the horse swallows, the feed enters a simple stomach that is relatively small (8 to 19 quarts) and has an acidy pH. Stomach retention time is relatively small before passing into the small intestine. The small intestine is about 70 feet long, relatively small in diameter, and holds about 65 to 70 quarts. The pH in the small intestine and the rest of the digestive system is pretty neutral. The stomach and small intestine are primarily responsible for digesting and absorbing most of the starch, protein, fat, fat-soluble vitamins (A, D, and E), and most of the minerals. The starch (soluble carbohydrate) absorbed here is converted into glucose and used as energy or stored as glycogen to be used later.

Material not digested in the stomach or small intestine pass into the cecum, large colon, and small colon know collectively as the large intestine or hindgut. The large intestine is very large and holds from 21 to 24 gallons of liquid and feed material. This is the primary site for fiber digestion. Since the horse does not have any natural enzymes for digesting plant fiber, the large intestine contains billions of bacteria responsible for fermenting the fiber into energy (volatile fatty acids) and micronutrients B vitamins and Vitamin K) the horse can use. One of the primary volatile fatty acids is proprionic acid, which is also commonly used as a preservative in feed to prevent mold. The large intestine is also the primary site for phosphorus absorption, important for skeletal growth, muscle contraction, and energy utilization.

The large intestine is actually the main engine of the horse and is essential to the overall health of the animal. Without maintaining a healthy hindgut, significant problems such as colic and laminitis can easily occur. Also, since the large intestine is responsible for synthesizing and absorbing B vitamins, including biotin, the health of the hindgut has a big influence on things you would not normally attribute to fiber digestion such as appetite stimulation and hoof and hair quality. Things you can do to help maintain hindgut integrity are:

   * Do not overfeed grain. Excess grain that does not get digested in the small intestine passes into the large intestine and ferments extremely well. The excess fermentation causes changes in the pH and excess gas. Both can dramatically increase to potential for colic or laminitis (founder). A good rule of thumb is not to feed more than 0.5% of body weight of grain in a single feeding.
   * Make sure clean, fresh water is available at all times at the right temperature. Dirty water or water that is too cold in the winter or too hot in the summer will inhibit consumption. The large intestine also serves as a large reservoir providing a reserve of electrolytes and excess water essential for cooling the body to sustain exercise. A lack of water will reduce the water required in the reservoir and will inhibit fermentation and material flow.
   * Fiber quality and quantity are primary in any horse's diet. Poor hay quality will cause loss of weight and hay bellies. Lack of quantity will cause an imbalance between grain and fiber and increases the potential of colic or laminitis. Another good rule of thumb is to make sure that the fiber portion of the diet is always a minimum of 50% of the total or diet or a minimum of 1% of body weight.
   * Reduce rapid fiber changes. Everyone knows not to change the type of grain overnight, but the same rule should also be followed with fiber. Ease into a new cutting or delivery of hay and gradually introduce the horse to new spring or different pastures. Early spring pastures can have as much soluble carbohydrates and grain.
   * Allow adequate turnout time. The same research that has proven that rapid fiber changes are a leading cause of colic also indicates that lack of proper turnout is also a leading cause.

Some indications that the hindgut is not functioning very well or that other feeding options need to be considered are:

   * Hay belly – indicates that poor quality forage is being provided. The large intestine will retain poor quality forages longer trying to get as much nutrition as possible. That will stretch the large intestine causing the hay belly appearance. Good quality forage will shrink the hindgut back to normal size.
   * Cow flops rather than road apples. Manure that more resembles cow manure often indicates that the fermentation in the large intestine is not functioning optimally. This often occurs with rapid fiber changes, excess grain, or just poor intestinal health often associated with age. Do not overlook the potential for diseases or illnesses required the attention of a vet.
   * Poor hair coat or hoof condition. Typically it would accompany one or both of the problems listed above.

Research and practical experience has taught us that the healthiest horses are those that are allowed to be horses by feeding on quality fiber on a continual basis. However, outside influences such as pasture availability, energy and work requirements, owner life styles, and etc. have an influence on the digestive system of the horse that are not always positive. We know a lot more today about feeding horses in the 21st century environment. Feeding for life styles, age and living conditions are now considered when designing feeds. Even forage alternatives and improved high fiber feeds are on the forefront of equine nutrition.

Horses, like people, are individuals. Each has their own metabolic rate and some are easy keepers while others are a bit more of a challenge. By understanding how the internal process works, we can better understand how to feed them to their maximum potential and limit feeding related problems."

If you would like a more detailed description of the digestive system of the horse, here is Ohio State University's Horse Nutrition Bulletin 762-00: (

"The Horse's Digestive System

The horse is a nonruminant herbivore. Nonruminant means that horses do not have a multi-compartmented stomach as cattle do. Instead, the horse has a simple stomach that works much like a human’s. Herbivore means that horses live on a diet of plant material.


The mouth contains 36 (females) to 40 (males) teeth. The wolf teeth are not counted as not all horses have them. Teeth are important in harvesting and chewing feed. The horse’s upper jaw is wider than the lower jaw, so sharp points often develop on the molar teeth. These points may prevent normal chewing which reduces the food value received from the feed and may predispose a horse to colic. Filing (or floating) the teeth will remove the points. Horses with a parrot mouth (overbite) or a monkey mouth (underbite) may also have difficulty in harvesting and chewing feeds.

Feeds are mixed with saliva in the mouth to make a moist bolus that can be easily swallowed. Three pairs of glands produce saliva – the parotid, the submaxillary, and the sublingual. Horses will produce up to 10 gallons (85 lb.) of saliva per day.


This is a simple muscular tube that takes food from the mouth to the stomach. Because the muscles in the cardiac sphincter valve leading into the stomach are very strong, it is almost impossible for a horse to vomit. It is more likely that the stomach will rupture in the event of an overconsumption of feed.


The stomach of the horse is small in relation to the size of the animal and makes up only 10% of the capacity of the digestive system. The natural feeding habit of the horse is to eat small amounts of roughages often. Domestication has brought a change to all this. Horses are now expected to eat large amounts of concentrate once or twice a day. This greatly undermines the horse’s digestive capabilities. It has been established that we can improve the digestive efficiency of a horse by feeding small meals often, but this has to be weighed against the labor costs of doing so.

In the stomach, food is mixed with pepsin (an enzyme to digest proteins) and hydrochloric acid to help break down solid particles. There are also bacteria present that produce lactic acid. It is believed that these bacteria may be important in the case of a ruptured stomach. Ruptured stomachs occur most often in foals at the time of weaning. The foal stops eating at weaning due to the stress associated with the dam being taken away. A few days later the foal decides to eat. If there is a large amount of grain available, the foal often overstuffs itself. Lactic-acid-forming bacteria ferment this mass of carbohydrate, producing high levels of lactic acid. This lactic acid causes paralysis of the pyloric sphincter, which normally lets the food out of the stomach. The stomach bursts from gas produced in the bacterial fermentation of the feed.

The rate of passage of food through the stomach is highly variable, depending on how the horse is fed. Passage time may be as short as 15 minutes when the horse is consuming a large meal. If the horse is fasted, it will take 24 hours for the stomach to clear.

It has long been a question as to what you should feed a horse first, grain or hay. Because of their density, grains tend to stay in the stomach longer, but it has not been proved to be advantageous to feed either first. Another question is whether a horse should get water before or after a meal. If you leave it up to the horse, he will usually drink a little as he eats, if consuming dry feeds. The best recommendation is to offer water free choice at all times.

Small Intestine

The small intestine of the horse is approximately 70 feet long and can hold up to 48 quarts. This is the major organ of digestion in the horse. There are many components to this digestive process. Pancreatic enzymes will help digest the food; carbohydrases digest sugars and starches; proteases break proteins down into amino acids; and bile from the liver is added to emulsify (break into smaller units) fats and to suspend the fat in water. Bile constantly flows into the small intestine from the liver because the horse does not have a gall bladder in which to store it.

After the food has been digested, it is absorbed through the walls of the small intestine and carried off by the blood stream to whatever cells need the nutrients. Nearly 50—70% of carbohydrate digestion and absorption and almost all amino acid absorption occur in the small intestine.

It can take as little as 30 to 60 minutes for food to pass through the small intestine.

Horses are very susceptible to colic or death from toxic materials in the feed. Unlike the cow that has bacteria in the rumen that can detoxify materials before they reach the small intestine, toxic material a horse may consume enters the intestine and is absorbed into the blood stream before it can be detoxified. Therefore, it is very important not to feed horses moldy or spoiled feeds. Urea is a feed supplement fed to cattle that can be utilized in their rumen to make protein. Horses cannot use this feed supplement because it is absorbed in the small intestine before it can get to the cecum where it could be used. Urea can be toxic to the horse, but the horse can tolerate the level at which it is added to most cattle feeds.


The cecum is a blind sack approximately four-feet long that can hold up to 40 quarts of food and fluid. The cecum is a microbial inoculation vat, similar to the rumen in a cow. The microbes break down feed that was not digested in the small intestine, particularly fibrous feeds like hay or pasture.

The cecum is odd in design because its entrance and exit are both at the top of the organ. This means that the feed enters at the top, mixes throughout, and is then expelled up at the top. This design is the cause of problems if an animal eats a lot of dry feeds without adequate water or if a rapid change of diet occurs. Both may cause a compaction in the lower end of the cecum, which in turn produces pain (colic). The microbial population in a cecum is somewhat specific as to what feedstuffs it can digest.

If a change of feed occurs, it takes about three weeks to develop a microbial population that can digest a new feed and maintain a normal flow through the cecum. A general rule for safely changing feeds:

   Week 1: Feed a mix of three-fourths of the old ration and one-fourth of the new ration.

   Week 2: Feed a mix of one-half of the old ration and one-half of the new ration.

   Week 3: Feed a mix of one-fourth of the old ration and three-fourths of the new ration.

   Week 4: Feed all new ration.

Feed will remain in the cecum for about seven hours, allowing bacteria time to start breaking it down. The microbes will produce vitamin K, B-complex vitamins, proteins, and fatty acids. The vitamins and fatty acids will be absorbed, but little if any protein will be absorbed.


The colon or large intestine is about 12 feet long and will hold 80 quarts. Food may reach here in a little as seven hours and will stay here for 48—65 hours. Microbial digestion continues, and most of the nutrients made through microbial digestion are absorbed here. In addition to the vitamins and fatty acids absorbed in the colon, water is also absorbed, resulting in fecal ball formation. These fecal balls, which are the undigested and mostly indigestible portion of what was fed, are then passed from the rectum."