Tour the Equine Digestive Tract

Ever wonder how your horse’s digestive system works? What goes on in there? Why are they so sensitive? And why should I divide the feed ration into 2 or 3 feedings per day? Let’s take a closer look to better understand.

The Equine Digestive Tract:

Digestive Horse Cecum_logo

Mouth & Teeth: Teeth are the beginning of the entire process. Designed to grind foodstuffs into smaller pieces, the act of chewing also stimulates three glands in the mouth to produce saliva. These glands can produce up to 10 gallons per day of saliva. The saliva contains bicarbonate (a natural acid buffer) and amylase (assists with carbohydrate digestion). Teeth are an important component to digestion and should be checked annually to insure proper function. A horse that is unable to effectively chew long stem forage, such as a senior horse, is at higher risk of impaction colic. If you have a horse like this, be sure to consult with your veterinarian for a comprehensive care and feeding program.

Esophagus: The purpose of the esophagus is to funnel food from the mouth to the stomach. Approximately sixty inches in length, this is a one-way passage. Unlike humans, horses cannot vomit. This is why horses who ‘bolt’ their feed (eat too fast and don’t chew adequately) can get into trouble and feeding practices need to be adjusted to reduce the risk of bolting feed.

Stomach: Small in size compared to the rest of the horse’s body, food will only spend about 15 minutes in the stomach before it moves on. The stomach is designed to function best when it is ¾ full; therefore, care takers are encouraged to provide horses with a steady supply of forage throughout the day. Because of the small size, a horse should not be fed more than 0.5% of body weight in one meal. Meals of grain are best divided into 2 or 3 portions per day.

Small Intestine: After leaving the stomach, food will spend anywhere from 30 to 60 minutes here; a good thing with the many nutrients that are absorbed. Nutrients such as proteins (amino acids), vitamins A, D, E and K, calcium, phosphorus, and other minerals along with starches and sugars. Cereal grains such as oats, barley, and corn that are high in carbohydrates (starch and sugar) are easily digested here. The horse doesn’t have a gall bladder, so bile from the liver flows directly into the small intestine to aid in the digestion of fat.

Large Intestine: is comprised of the cecum, large colon, small colon and rectum.

  • The cecum is located on the right side of the horse and is where fiber is digested and converted to energy and heat. The shape of the cecum is unique because the entrance and exit are located at the top of the organ. Able to hold up to 10 gallons of food and water, the cecum contains populations of bacteria and microbes which further break down food (fiber) for digestion and absorption. These microbes are accustomed to digesting a horse’s ‘normal’ diet, so any adjustments in feed or forage should be done slowly, allowing the microbes to adjust.
    • If a horse consumes too much starch in one meal, it is unlikely to be digested fully in the small intestine. It would pass through the small intestine into the cecum where the microbial organisms rapidly ferment the starch, producing excessive gas and lactic acid that could ultimately cause digestive upset or colic.
  • The large colon continues the digestive process by absorbing additional fiber components and water. This is where B vitamins are absorbed.
  • The small colon is where excess moisture is reclaimed to the body. This is also where the formation of fecal balls occurs.
  • The rectum is where the fecal balls are expelled.

With this short tour and explanation, we hope you have a better understanding of how your horse digests and absorbs nutrients, and that this also sheds light on why good feeding management and regular dentistry care are important aspect for the digestive health and overall well-being of your horse.

Pre and Probiotics in Horse Feed

While scanning information about various horse feeds, you may have come across the phrase ‘contains prebiotics and probiotics’….Hmmm, sounds impressive, but what are they, what do they do for your horse, and why are they important?  Pre- and probiotics are considered “functional ingredients” that are added to horse feed to provide benefits to your horse. Here is some information about them and what they can mean for the digestive tract and overall wellbeing of your horse.

Healthy, inside and out
Rosie shows a dappled coat, indicating good health shining from the inside out.

It starts with the gut. The environment of the intestine (a.k.a. gut) contains naturally occurring beneficial microorganisms commonly called  ’bugs’. Gut bugs are found in all species, including humans, and are essential to the digestion process. For the horse, gut bugs work to break down components of forage and feed as they pass through the digestive tract.  The bugs deconstruct complex molecules within feedstuffs, which releases nutrients and allows the synthesis of energy substrates and important vitamins. Those nutrients are then absorbed through the intestines into the bloodstream, where they become available to cells in the body to support basic maintenance, growth and activity.

Feed that is broken down and digested more completely allows for more nutrients to be readily available for absorption.  This is essentially what probiotics do. Adding probiotics to a horse feed means adding more beneficial bugs to the existing population in the horse’s gut. Probiotics such as yeast culture, work with the naturally occurring bug population to enhance the digestive process, further breaking down complex protein and fiber fractions in the gut and making them more available for absorption into the blood stream. As a probiotic, yeast culture has also been shown to balance and stabilize the digestive microbial ecosystem in the cecum of the horse, as well as help prevent the colonization of bad bacteria in the gut.  A stable microbial ecosystem is beneficial to the horse beyond improvements in digestive and absorption efficiency, it also reduces the risk of digestive upset, such as gas colic, that a horse might experience with changes in feed or hay, or while under stress from transportation, shows, changes in weather or other.

Prebiotics can be thought of as an energy jolt for the gut bugs.  Prebiotics are a rich nutrient source for the gut bugs (e.g. lactobacilli, bifidobacterial) which in turn stimulates their growth and activity, making them more effective at their job. Research has shown that prebiotics help stabilize the population of gut bugs even through sudden changes in the diet, which helps to reduce incidents of digestive upset.  For performance horses who require energy dense diets that include higher levels of starches and sugars, prebiotics can help reduce the incidence of digestive disorders and support optimal performance.  Prebiotics such as inulin and oligofructose are selectively fermented by the gut bugs, stimulating their growth and activity, which benefits the horse by enhancing the absorption and retention of certain minerals, which in turn can support the immune system, skeletal tissue, and more.

The population of bugs in the gut are sensitive to changes in their environment brought on by stress, illness or the ingestion of undesirable materials .The addition of pre- and probiotics to a diet has been shown to be beneficial in reducing the incidence of digestive upset, namely diarrhea. For senior horses, the use of pre- and probiotics in feeds has been shown to improve the digestibility and absorption of nutrients, which can translate into an enhanced quality of life.  In summary, pre- and probiotics work with the naturally occurring gut bugs to support optimal gut health, aid in the digestion process, as well as provide a buffer against negative bacteria.

Carbohydrates in Horse Diets

There is a lot of discussion these days about carbohydrates, the good and the bad.  In reality, they are all related.  Carbohydrates contain carbon, hydrogen and oxygen in varied chemical relationships. 

  • Sugars are the simplest of the carbohydrates and can be simple sugars such as glucose or more complex sugars. 
  • Starches are strings of sugars linked together in such a way that most starches can be broken down into glucose by the action of enzymes, primarily amylase. 
  • Fibers (lignin, cellulose, hemicelluloses etc.) are also chains of sugars that cannot be broken down easily by enzymes and must be fermented by the animal to release the energy. 

Starches and sugars are produced by plants as a means to store energy, so they contain energy that is more readily available than the energy in fiber.

Because horses produce less amylase, the enzyme used to break down starch, than some other animals, say perhaps pigs, they are more limited in their ability to digest large quantities of starch. However, they digest smaller quantities very efficiently and very effectively! 

Starches and sugars are a fairly concentrated source of Calories to be used as a source of energy when extra energy is required to maintain body condition and do more work.  In the wild, horses would consume seed heads (grain) when available in the fall to help them gain weight (added Calories) to be ready for winter, so starches and sugars are a part of the diet in horses in the wild.  Today’s working horse requires Calories, and a combination of fiber, starch, sugar and fat can be the best way to support the horse to maintain the balance of optimal health and optimal performance.

High-Fat Horse Diets: Performance Horses

A high-performing horse can have up to twice the calorie requirement as the same horse in a maintenance stage. Owners and trainers of performance horses often give more feed to meet that calorie need. Because horses can use fat as a calorie source efficiently, and fat contains more than double the calories of starch, high-fat horse feeds make perfect sense to increase the energy intake without greatly increasing the quantity of feed needed. 

Feeding higher-fat, controlled starch level feeds can play a role in lowering the chance of colic and laminitis by reducing the amount of starch (carbohydrates) in the ration.  Here’s why: 

  • Horses with a very high grain ration are often at risk because high levels of grain feeding can cause a starch overload in the small intestine and cecum.
  • Overloading the small intestine with starch allows that extra starch to pass in to the cecum and large colon, which is where forage is digested.
  • Fiber digestion is accomplished by the bacterial and protozoal populations residing in these organs. When starch enters the cecum the pH drops and this bacterial population dies.
  • This can result in a cascade of events that may include colic, laminitis and death.

Keep in mind that starch is still a crucial part of a horse’s diet, and is required for proper muscle function.  As horse owners, it is best to work towards an optimal balance of all nutrients in the diet, not the use of one to replace another.   A proper balance of controlled starch levels, along with increased fat levels in the horse feed, will help deliver a horse that is ready to go and has the fuel in the tank to keep on going.

Feeding Fat to Horses

Lately there has been tremendous interest in the horse world about fat. In regards to human nutrition, “fat” is often considered a bad word, and low-fat diets are popular. But we should remember that in people, some fats are necessary and healthy. This is equally true for horses: fats play a very important role in horse feeds and nutrition.

There are many reasons to feed horses added fat. The best reason for using added fat is for an energy (calorie) source. The primary purpose for grain feeding is to provide energy for maintenance, performance, growth and reproduction.  Because fat contains more than twice the calorie content of starch, and horses digest and utilize fat well, higher fat horse feeds offer an excellent opportunity to increase calorie intake without greatly increasing the quantity of feed.

Other reasons for adding fat to a feed ration include improved endurance, heat tolerance, hair coat and attitude:

  • Horses on fat supplemented diets experience increased endurance because of a glycogen sparing effect. Glycogen is the fuel for muscular activity that is stored in the muscle cells. Horses that are on high fat diets conserve glycogen, which can help them finish a performance event stronger. This is particularly important in racing, eventing, cutting and other activities that require high performance over time.
  • Horses trained in hot, humid environments show improvement to heat tolerance because fat supplemented rations generate less heat as a by-product of digestion. This becomes important in parts of the country where heat is prevalent.
  • A shiny hair coat, a side benefit of added fat in the diet, is important to horse owners who are showing or selling horses. Higher fat levels, especially those that contain a balance of omega three and omega six fatty acids, are good choices for those in the show ring or sale ring business.
  • Horse owners often report that horses that are fed lower-starch diets with added fat have a calmer attitude than those that are fed a conventional high starch and forage diet.

It is important to keep in mind that indiscriminate fat supplementation can create deficiencies of other nutrients. This is known as empty calories; where energy levels are adequate, but protein, lysine and mineral levels are not. Developmental bone problems can result which may precipitate injuries in young horses.

There also is a period of adjustment of about three to four weeks for horses to receive benefits from added fat. Any change in diet should be done gradually over seven to10 days to avoid the possibility of digestive upsets.

A balanced diet, tailored to the use and age of the horse, is the most important consideration. A trained nutritional consultant can make recommendations that will best fit your horse and the activity involved.

Fiber in Horse Feeds

In our previous post, we learned what fiber is and how a horse digests it,and we also learned that a horse consuming 1-1.5% of it’s bodyweight in quality roughage will satisfy its daily fiber requirements.

When it comes to any grain sources that may be added to your horses diet, fiber plays a much smaller role since the amount of fiber that is added by grains is relatively little, but the effect and digestive process is similar. 

When feeding the grain portion of the diet, ensure that your horse is not receiving high quantities of grain meals all at once – typically no more than 5-6 pounds of grain per meal at most. Because grains tend to be higher in starch than roughage, feeding too much at once can overwhelm the small size and quick rate of passage of food through the stomach and small intestine, and allow starches to pass undigested to the hindgut. Digestion of starches in the hindgut releases lactic acids that are toxic to the fiber-digesting microorganisms, which can result in a gas colic episode or laminitis.

Generally speaking, when you look at a the tag from a basic equine ration, the higher the crude fiber level listed, the lower the energy content of the feed.  Of course, there are other factors that must be looked at, such as the fat level, and also possibly the sources of fiber. 

Beet pulp, for example, is often referred to as a “super-fiber” due to the high level of fiber it provides while also providing roughly the same energy level as oats.  While soy hulls and dehydrated alfalfa are common ingredients used to increase fiber levels, a performance horse ration with a higher fiber level may make use of beet pulp to achieve both increased energy and increased fiber levels.

Managing Horses with Gastric Ulcers

Last week a horse owner contacted me about changing her horses diet.   She stated that they are ¾ of the way through show season and he is just “off his game”.  It seems that the horse was showing a lack of appetite and not finishing his grain. In addition, his disposition seemed to have changed, being rather grumpy and his performance level was suffering.  A few times he had shown signs of mild colic over the past two months.

I suggested the owner contact her veterinarian, as it sounded like the horse may have an ulcer.  I explained that the percentage of horses with ulcers continues to increase, and that higher intensity levels of training are correlated with an increase in ulcer incidence.  The ulcers often occur in the upper third of the stomach, which does not have a mucus layer and does not secrete bicarbonate that helps to buffer stomach acid.  It is also interesting to note that ulcers have not been founded on pastured horses.  This is likely due to the fact that as a horse grazes, it produces large amounts of saliva, which contain the bicarbonate and amylase needed to provide a buffer for the stomach lining. 

The owner was not pleased with my answer, but agreed to call the vet.  Within the week she contacted me and said the horse had been diagnosed with a gastric ulcer.  He was now on medication, but we needed to make dietary changes as well.  I suggested the following “back to basic” steps to help manage her horses condition:

  1. Allow the horse to be turned out or hand grazed.
  2. If access to pasture is not possible, good quality hay is a must.  Recent studies indicate that legume hay is an excellent choice, possibly due to the high calcium content which may help to serve as a buffer.
  3. Breaking the daily rations into smaller more frequent meals also help keep saliva production constant and protect the stomach lining – more like “grazers” instead of “meal eaters”.
  4. High starch diets also tend to aggravate ulcers due to increased acid production. A high fat high fiber feed is ideal.

In essence, to help keep them from suffering the ill effects of ulcers,  we need to let our horses just be horses.

Feeding Bran Mashes to Horses

Feeding bran mashes to horses is a common tradition dating back a long time, and is often thought to be a help in preventing colic through a laxative effect. Bran is believed to be a laxative in people, but to get that effect in horses, you would actually have to feed it in quantities bigger than your horse could eat.  Some horses do produce softer stools the day after eating bran, but this probably reflects bran’s tendency to irritate the lining of equine intestines.  If fed daily over a long period of time, bran may actually contribute to the formation of enteroliths. 

The bigger danger in feeding bran to horses is the calcium:phosphorus ratio of bran.  Calcium and phosphorus work together to build sound bones and assist muscle function.  To do so, they must be absorbed in appropriate proportions (preferably 1.2 or more parts calcium to 1 part phosphorus).  If, over a long period of time, phosphorus exceeds calcium in the diet, the horse’s body will pull extra calcium from the horses bones to meet it’s needs, and eventually weaken the skeleton.

Wheat bran and rice bran contain approximately 10 times more phosphorus than calcium.  Therefore, an occasional bran mash won’t harm the horse, and he will likely relish the treat.  However, daily bran regimens in large quantity should be avoided, unless calcium is supplemented in sufficient quantities elsewhere in the diet.

Management Practices: Reducing the Risk of Colic

Colic is one of the leading health problems facing horse owners. According to the USDA’s National Health Monitoring System (NAHMS) Equine Study 1998, about 4% of the horse population experiences colic each year. Colic rated second only to old age as the cause of death in equines. The same study indicated that horse owners most commonly identified “unknown” causes for colic, followed by gas colic and feed related.

Feeding management and non-feeding-related management practices can all have an impact on reducing the risk of colic.

The following management practices can aid in reducing the risk of colic:

  1. Parasite Control: Includes proper sanitation and regular deworming per program.
  2. Dental Care: Be sure to schedule regular dental exams as needed.
  3. Fresh Clean Water: A lack of water in both cold and warm weather may increase risk of colic.
  4. Consistent Diet: Avoiding sudden changes in either hay or grain may help reduce risk.  A survey by Dr. Noah Cohen et al in Texas indicated forage changes are associated with colic more frequently than changes in the grain portion of the diet.
  5. Avoid Starch Overload. Starch overload, or allowing undigested starch to get to the hindgut, is a major cause of gas colic.  Limiting meal size, maintaining equal feeding intervals, and selecting controlled starch feed products for a feeding program, may help reduce the risk of starch overload. 
  6. Feed Additives. Some feed additives, such as direct fed microbials and yeast culture, may also be beneficial in improving forage utilization and digestion.

Colic prevention—rather than colic treatment—is clearly much better for both the horse and the horse owner.