Gastric ulcers are lesions that are found in the stomach. The stomach of the horse is made up of two regions, the upper "squamous" region which has a thin cell wall lining and the lower "glandular" region which has thick cell wall lining.  The glandular region is where gastric acids are secreted to assist the digestion of food, and so the pH is usually very acidic (pH 4).  The squamous, thin walled area of the stomach is less protected by mucous than the lower region.  The majority of ulcers are found in the thin walled area where food first enters the stomach

Digestion in the stomach.
Horses were designed to eat fibrous plants, and were not designed to eat large amounts of high grain (high NSC >12) diets. NSC is the sugar and starch or Non Structural Carbohydrate in the food. Food flows through the oesophagus and enters the upper region of the stomach where the pH is usually 5-6 ie not very acidic. The very soluble proteins and carbohydrates are broken down here by the enzymes in the saliva. The food then passes to the very acidic glandular region, where it is aggressively broken down by the gastric acids.

What causes ulcers.
There are many factors that can cause ulcers including stress and parasitic infection. One of the most common causes however is diet, and how it is fed. When horses are fed high grain (high NSC) diets, the sugars are also digested in the non glandular region, causing a very sharp decline in pH and highly acidic conditions. Because the squamous cells are not well protected by mucous, these cells can be damaged by the acids, and cause ulcers. 

Simply feeding low NSC (non grain) feeds is one way of avoiding the possibility of diet related ulcers. Horses normally eat little and often, usually grazing 18 hours a day, ie they are ?slow feeders?. With our modern and busy lifestyle, it is usually only possible to only feed twice daily, morning and night. This is not really and issue with hay, because it is slowly digested, and the horse will eat it slowly.

However the dilemma occurs when we require performances from our horses. To achieve high energy intakes we generally feed highly palatable grain based feeds twice a day and this can be the basis for real problems. Feeding high NSC feeds twice a day is called shock/pulse feeding. These high NSC feeds are eaten quickly, and to assist digestion, large amounts of gastric acid are released into the stomach, including the upper region. 

A further compounding factor with pulse feeding is that the horse can have an empty stomach for long periods between feeds, during which time the stomach acid can drop to a pH of 2. So how can you feed to avoid ulcers and still achieve high energy intake to achieve peak performance from your horse? There are several strategies ? which can be used both separately and in combination:

1. Select a low grain (low NSC <12%) feed
2. Feed little and often to avoid pulse/ shock feeding
3. Select ?slow high energy foods?, ie high energy feeds that do not cause highly acidic gastric conditions or glucose ?spikes?.  For further information see http://www.stanceequine.com/mediaroom_detail.php?Feeding-Slow-and-Fast-feeds-to-horses-94
4. Have hay available to avoid the stomach emptying

The problem with treating only the symptoms.
Previously we have presented the management, feeding conditions and science relating to horses becoming susceptible to gastric ulcers. In addition, the clinical signs of horses with ulcers, together with the veterinary diagnostic process and medication to successfully treat have been presented.

In the busy life of the horse owner it is convenient to ?treat the symptoms? and not treat? the cause?. The above discussion describes many methods to treat horses to attempt to prevent ulcers. Adding medication or preventive agents to the feed is convenient. Many of these treatments however ignore the underlying cause of ulcers, i.e. feeding high NSC (high sugar and starch) diets.  Continued feeding of high NSC diets, together with treatment to avoid ulcers could in fact be causing longer term problems including insulin resistance and laminitis. Now we will outlines the potential complications of continued feeding high NSC diets and treatment to prevent ulcers.

The anatomy of the GI tract
The gastro-intestinal "GI" tract that illustrates the stomach as a comparatively small component [<10%] of the total digestive tract. Secondly, as can be seen, it is a relatively short and simple compartment designed for rapid transit of food to the small intestine. The diagram also highlights the large caecum [>3 times the stomach volume] at the end of the small intestine. This anatomy means that horses are "hind gut fermenters" as distinct from cattle which are fore gut fermenters. The caecum allows for digestion of the fibrous diet by microbia, and the subsequent extra nutrients are absorbed in the colon. Overall digestion is efficient and in fact synergistic if the pasture being selected and eaten has a moderate to low NSC content. This GI tract has served horses well especially when grazing a roughage pasture for > 18 hours daily. This anatomy is designed for ?slow feeders?.  

Feeding high NSC feeds can cause ulcers in the stomach simply by causing increased acid secretion.  High NSC feeds can cause major complications further down in the small intestines and the hindgut, causing acidosis.

Other articles in this series describe the potential harm of high NSC feeds on the small intestines and the hind gut.  If dietary NSC is not managed, and horses are overfed and underworked, then the horse could be predisposed to insulin resistance, obesity, Cushing's disease, laminitis bad behaviour and trying up.

Some more science that is useful
Recent studies demonstrate the usefulness of "slow high energy foods" i.e. low NSC diets for horses in yards and stables. Until recently, most horse owners did not have the option of a high energy feed  with low non-structural carbohydrates "NSC" for their performance and/or hard working horses. New low NSC high DE feeds such as coconut meal are now available that reduce the risk of ulcers, and the other sugar and starch related disorders.

Conclusion
Treating ulcers without addressing the underlying cause can cause major long term metabolic problems in horses.  High NSC feeds are a major cause of stomach ulcers and hindgut acosis.  Treating ulcers is simply treating the symptoms, and could potentially be ignoring the potential for other long term problems such as obesity, insulin resistance, tying up and laminitis.  All caring horse owners should assess the level of NSC provided, avoid pulse feeding, and avoid overfeeding and under working.