One of the most common problems that occurs in horses is gastric or stomach ulcers.  One reason is that although saliva is a buffer that increases the pH in the horse’s stomach to protect the stomach from the gastric acid that causes ulcers, horses only produce saliva when they chew but they can produce stomach acid 24 hours a day.  So, this works great for horses that are out in pasture grazing all day, but is a problem for horses that are fed only twice a day with no turnout.  This is why 90% of the racehorses have ulcers:  horses were designed to eat small meals over the majority of the day and not to be stalled and fed large amounts twice a day. 

As far as the horse’s stomach, the stomach of a mature 1100-pound horse can hold about 2 to 4 gallons of fluid. and food can be retained in the stomach for 1 to 5 hours depending on the type and consistency of it.  Treatments to prevent gastric ulcers include the drug omeprazole, and although it increases the pH by decreasing gastric acid, this is not without potential adverse effects.  The pH of the horse’s stomach is low to prevent bacteria from growing in the area and if you increase the pH to prevent ulcers, the bacteria could proliferate and allow an infectious process to develop.  Also, using omeprazole can have an effect on calcium balance and increase the risk of fractures.  However, a 2015 study showed no difference on calcium levels and bone density after 60 days of treatment, but the study only lasted 60 days and involved compounded omeprazole that may not be effective. 

Considering the size of horses, they have a short, small intestine and do not have a gall bladder, so bile is continually produced for digesting fats.  However, they have a long and complicated large intestine, and in contrast to ruminants in which microbial fermentation occurs in the first section of the stomach, their microbial fermentation occurs in the large intestine.  A horse’s stomach is similar to a human’s in that regard. 

The Waltham Center in England says the foundation of a horse’s diet should be forage, and many horses do not need additional feed other than added vitamins and minerals.  Forage is not only important nutritionally but is necessary for normal function of the GI tract.  Horses that are on pasture 24 hours a day generally graze about 60% of the time, and most normal horses need about 1.5% of their body weight a day which in a 1000-pound horse would be about 15 pounds.  That 15 pounds includes hay and grass.  However, some ponies will consume up to 5% of their body weight per day in a 24-hour period and will consume 1% within the first 3 hours of turnout.  This is one reason many ponies are fat and develop laminitis and founder.  If a horse is stabled 24 hours a day, then 100% of their forage needs to come from hay but if they are out to pasture 4 to 8 hours per day, feed only 50-75% of calculated hay ration, and if out on pasture 8 to 12 hours a day, feed only 25-50% of the calculated hay ration.  If your horse is on pasture 24 hours a day, then feed less than 25% of the calculated hay ration depending on the quality of the pasture.

Complementary feeds are those given to increase nutrition in horses that need some extra for work or pregnancy.  The veterinarians at Waltham Nutrition say that complementary feeds were considered to be high in energy and rich in cereal grain, but this is no longer the case.  Today’s complementary feeds deliver energy from a variety of sources ranging from high starch cereal grains to highly digestible fiber such as sugar beets.  Many of these feeds are supplemented with vegetable oil as a fat source and they also contain a vitamin and mineral supplement to balance the diet.  However, you have to give the recommended amount of feed, which is usually about 2 pounds per 1000 pounds of horse to meet the mineral requirements.  If the label recommends 2 pounds per day and you are only feeding 1 pound, you would need to add another supplement.  Ration balancers are also available that provide protein, vitamins and minerals if fed at the recommended amounts but do not provide energy, and this is a good option for those horses in light work that are on forage and you just need to balance the ration. 

Although it was common in the past to feed one cereal grain such as corn, when feeding a straight ration with only one ingredient you have to be careful because cereal grains are high in phosphorus and low in calcium while sugar beet pulp and alfalfa are high in calcium and low in phosphorus.  Feeding a straight ration with one ingredient can lead to an unbalanced ration and potentially cause disease.  For this reason, it is probably better to use a commercial feed that has been analyzed rather than trying to mix your own ingredients.     

Water is the most important nutrient in a horse’s diet. Normal water intake is required for normal function of all organs, especially the GI tract.