Horse Foregut and How a Prebiotic Can Help Reduce Risk Factors

How Do Prebiotics Work in the Horse Foregut? How Do Prebiotics Help My Horse?

Before answering these two common questions about prebiotics and the horse foregut of the digestive system; it helps to have an understanding of some basics of the horse’s digestive system. The horse digestive system is divided into two parts as shown in the photograph: The foregut, and the hindgut. Each have very different functions. The foregut, shown in pink, is comprised of the esophagus, stomach, and small intestine. The hindgut, shown in orange, includes the cecum, large colon, and the small colon. This article will address the benefits of prebiotics in the foregut. The hindgut and probiotics will be covered in a separate article.

The Horse Foregut

  • The foregut comprises only 37% of the digestive system. After feed is swallowed via the mouth and esophagus, it moves to the stomach and then the small intestine.

The Horse Stomach:

  • The stomach is small (holding about 2-4 gallons), and makes up only about 10% of the whole digestive system.
  • Normally food remains in the stomach for about 30-45 minutes. 
  • The rate of passage of feed 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.
  • The stomach is designed to digest small amounts of food in a continuous flow; it is never more than two-thirds full.
  • The stomach’s job is to breakdown food in preparation for digestion. Parietal cells continually secrete acid, activating enzymes that break down the proteins in foods, and also killing microorganisms in feed, reducing the potential for infection.
  • If large meals are eaten too quickly, food may pass into the small intestine before it has been sufficiently broken down by the stomach’s digestive juices
  • Gastric ulcers can occur in the squamous portion of the stomach from excess acid or improper digestion.

The Horse Small Intestine.

  • The small intestine has three parts: the duodenum, jejunum, and the ileum
  • Is about 60-70 feet in length and holds about 10-12 gallons.
  • The small intestine is  where ab­sorption of fats, protein, simple carbohydrates, vitamins, and minerals takes place.
  • Food passes through in 1-3 hours. Pelleted feed will pass through the small intestine more quickly than fiberous feed such as hay and textured grains..

PREBIOTICS: What They Are:

  • Mannan Oligosaccharides (MOS), are extracted from the outer wall of the yeast cell. Bio-Mos® is the registered trademark for a type of MOS developed by Alltech.
  • Bio-Mos® is a non-digestible carbohydrate , consisting of a long string of sugar molecules; the horse’s gut does not digest it, or break it down.
  • Bio-Mos® is a “food” that stimulates growth and activity of good bacteria in the horses’ gastrointestinal tract
  • Bio-Mos® has the same binding surface as the walls of the small intestine, so pathogens (bad bacteria) bind to it and are carried out through the digestive tract with the waste rather than remain in the gut to cause illness or disease.


  • Prebiotics such as Bio-Mos® support the foregut and the horse, beginning work in the stomach by altering the pH, thus reducing the chance of gastric ulcers.
  •  The small intestine helps prevent pathogens from reaching the hind gut. A prebiotic, such as Bio-Mos®, binds with these bad bacteria, and carries them through the digestive tract and out with the waste.
  •  When pathogens are present they can damage the integrity of the gut wall, and increase the chance for ulcers. Removing the pathogens can help the gut wall return to normal.
  • Prebiotics provide extra food for the good bacteria to survive and increase. If the horse eats too much grain too quickly so that it passes into the small intestine before it is fully broken down by stomach acids, or, if you are changing feeds, prebiotics can help the gut adapt without upset.
  • The small intestine is where most nutrients are absorbed in the gastrointestinal tract. The increase in good bacteria improves the absorption of nutrients from the diet.
  • A prebiotic such as Bio-Mos®, provides support for the digestive tract, the horse’s largest immune system
  • A healthy digestive system means a healthier horse

To learn more details about the digestion that takes place in the horse foregut,’s-foregut
should be helpful.

You might find the information at Colorado State University helpful in explaining more details about the digestive system:

Hygain feeds in Australia also has a detailed explanation:

It is impossible to cover every aspect of equine nutrition here. Your veterinarian can help you design a feeding program that is right for your horses, and provide important information about dietary-related illnesses such as obesity, founder, ulcers, colic, and orthopedic disease. There are also good books available on equine nutrition–ask your veterinarian to recommend one .