Gastric Ulceration & Colic

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Horses in hard work are traditionally fed a diet that is relatively high in hydrolysable carbohydrates (starch & sugars). In some performance horses such as racehorses, this is often combined with a restricted forage intake, as either hay or haylage. This common diet in combination with other management practices and environmental stressors increases the risk of the development of digestive disorders such as gastric ulceration (Bell et al., 2007b) or various forms of colic (Archer & Proudman, 2006)(see table 1).

Gastric Ulcers Colic
Meal Feeding Large Meals
High Starch Diet High Start Diet
Restricted Forage Intake Restricted Forage Intake
Lack of Grazing Abrupt Change to Diet
Intense Exercise Travel
Prolonged NSAIDS

Table 1: Feed related factors involved in the development of gastric ulcers & colic.

Are gastric ulcers a Man made disease?

Gastric ulcers, which are most often located in the non-glandular region of the stomach, have been identified in a wide range of horses including performance horses, and those engaged in leisure type activity and even in broodmares (Le Jeune et al., 2008). However, there is no doubt that the incidence of gastric ulcers is greater in horses in hard work, such as racehorses, eventers and showjumpers, that are more likely to be subject to many of the risk factors described above (see table 2).

Concentrated feed increases the risk of colic in horses.

Gastric ulceration arises from the prolonged exposure of the relatively unprotected areas of the stomach to the aggressive effects of gastric acid and other enzymes involved in the breakdown of protein. The horse is unusual in that as an evolutionary grazer, it secretes gastric acid continuously. However, both the physical presence of food in the stomach and the secretion of bicarbonate rich saliva offer some protection for the stomach mucosa against the ravages of gastric acid. The negative impact of diet on the development of gastric ulcers is probably brought about through its effect on both gastric acid secretion and on the secretion of saliva. Certainly the characteristic high starch – low forage ration of many performance horses is central to the development of gastric ulcers when combined with other management and environmental factors.

Population Prevalence (%) Reference
Racing (Thoroughbred)







Endurance Horses

Showing Horses


Leisure Horses

80 – 90




72 – 88







(Hammond et al., 1986;

Vatistas at al., 1999;

Johnson et al., 2001;

Begg & O Sullivan, 2003;

Bell et al., 2007a)

(Jonsson & Egenvall, 2006)

(Mitchell, 2001)

(Nieto, et al., 2004)

(Hartmann & Frankeny, 2003)

(Chameroy et al., 2006)

Table 2: Prevalence of gastric ulcers in horses engaged in different equestrian sporting disciplines.

Is crib biting a coping mechanism for gastric ulcers?

Oral stereotypic behaviour such as wood chewing or crib biting has previously been suggested to be an indication of the potential presence of gastric ulcers in horses, and it has been suggested that the stereotypic behaviour may be an attempt by the horse to stimulate the flow of saliva (Moeller et al., 2008).

Gastrin is a hormone produced by specialised cells in the stomach that stimulates gastric acid secretion. High starch rations have been shown to extend the secretion of gastrin for longer following feeding, which could result in greater exposure to gastric acid (Sandin et al., 1998). This is more likely to be an issue when forage intake is restricted, and so the protective effects of bicarbonate from saliva are reduced due to deceased chewing. Remember that as well as being physically restricted, a horse may self-limit forage intake when the intake of concentrate is high, and so reducing starch intake and extending the time spent eating forage is desirable. Other components in the diet such as ‘antacid’ ingredients e.g. aluminium hydroxide, magnesium hydroxide or calcium carbonate may also offer some transient protection during this critical period following feeding (Clark et al., 1996).

Fermentation can occur in the stomach

There has been some recent research published that suggests that the local fermentation of starches and sugars within the stomach may further contribute to gastric ulcer development. Exacerbated by large meals, this fermentation leads to the formation of volatile fatty acids (VFA) such as propionic, acetic and butyric acids. These VFA’s become more fat soluble in the acidic environment in the stomach and so their potential to damage the cells of the gastric mucosa increases (Nadeau et al., 2003). Reducing meal size may help to reduce fermentation in the stomach but other nutraceutical ingredients such as fructo-oligosaccharides (FOS) show some potential benefit.

The action of FOS was originally thought to be limited to the large intestine, but recent research reports its additional action in the stomach (Respondek et al., 2005). Although the balance of microflora in the stomach in this trial was not changed significantly through the addition of FOS to the diet, there was a tendency for the level of lactate utilizing bacteria to be increased. Perhaps more interesting was the fact that gastric pH was increased in those horses supplemented with FOS, leading to speculation that this may offer potential benefits in maintaining gastric health (see fig 1). Whilst supplements that combine ingredients of this nature, should not be regarded as an alternative to veterinary medication, they may have potential for use in horses as an adjunct to veterinary treatment for those at risk from gastric ulcers. They may also be useful following recovery, particularly for horses racing or competing under other competition rules, where anti-ulcerogenic veterinary medicines cannot be used.


Other feeding factors that may be beneficial to incorporate into the diet of performance horses include:

  • Alfalfa – Represents an additional form of forage to stimulate chewing and saliva flow. But in addition, the high protein content of this forage and some of the amino acids present have the ability to ‘buffer’ stomach acidity to reduce the likelihood of gastric ulceration (Nadeau et al., 2000).
  • Oil – addition of relatively low quantities of oil to the diet (45mls) has been reported to reduce gastric acid secretion and to increase the production of factors (prostaglandins) that stimulate the secretion of bicarbonate rich mucous, as well as blood flow to the stomach (Cargile et al., 2004). This effect needs further substantiation as these preliminary results were not reproduced in a later study (Frank et al., 2005).

The traditional high starch and low forage diet seen so commonly in performance horses also puts other areas of the equine digestive tract under pressure, particularly the hindgut. The hindgut is a well-developed region of the digestive tract that has specialised in the fermentation of fibre to produce volatile fatty acids. These provide a major energy source for all types of horses. The hindgut is also, however, instrumental in the re-absorption of water and electrolytes and the synthesis of water-soluble B vitamins. The presence of a large and diverse population of microflora, including bacteria, yeasts and protozoa, help to achieve these functions. Many of the digestive ailments to which horses are susceptible, such as scouring, colic and even laminitis can be attributed in part to disruption in the healthy balance of microflora in the hindgut.

The population of microflora in the hindgut is not static and adapts to the nature of the horses’ diet as it also provides an essential food source for the resident bacteria (Fombelle et al., 2001; Julliand et al., 2001).

The population can also change in response to dietary induced changes in the level of acidity and oxygen present in the hindgut. For example, the population of microflora in the hindgut of horses fed a high fibre diet will be somewhat different to that found in horses chronically fed a high starch and low fibre diet, where a significant quantity of starch escapes digestion in the small intestine to reach the hindgut.

Dietary change and high starch diets put horses at risk of colic

The risk of digestive disturbance such as colic is heightened significantly when concentrate feed intake is increased, (Tinker et al., 1997), (fig 2) especially where high starch diets are fed. In addition, the risk of colic is also increased during an acute change in the content of the diet. These effects are probably brought about through the impact of diet on the balance of microflora in the hindgut and how this affects the pattern of fermentation therein, as well as the level of acidity present.

Prebiotics support hindgut health

Ingredients such as prebiotics including fructo-oligosaccharides (FOS), which are commonly derived from chicory or sugar beet, potentially offer some support to help maintain digestive health. FOS cannot be digested enzymatically in the small intestine, but provides a selective food source to beneficial hindgut bacteria, promoting their growth. The beneficial effects reported for FOS may arise from the ability to limit the level of lactic acid produced during fermentation, particularly in the colon (Respondek et al., 2006). Lactic acid is produced by certain bacteria known as ‘lactate producers’, especially when readily fermentable substrates like starch are available, which can commonly escape digestion in the small intestine. FOS can therefore help to reduce the detrimental impact of high starch diets on the hindgut microflora helping to maintain digestive health. There is also some evidence that FOS can help reduce the likelihood of colic. Volter et al reported a reduced incidence of colic in a group of 126 horses supplemented daily with short chain FOS (Volter, 1999). These findings were then repeated in a subsequent trial, where the effectiveness was suggested to be related to the quantity of prebiotic fed (Julliand, 2006).


Bottom line

So whilst appropriate feeding and management are crucial to maintaining digestive health, both in terms of gastric ulcers and colic, there are a number of beneficial ingredients that are found within some feeds and supplements such as antacids and FOS that can offer further support. It is important when considering such products that regard is given to the presence of suitable scientific trials to support their effectiveness.