Diet is an influencing factor and the type of feed used along with the timing of feeding is important in the management of this condition.
Gastric ulcers are a common problem associated with performance horses, especially racehorses where the prevalence is highest. Murray et al.,1996 cited in NRC 2007 found gastric ulcers in 100% of horses actively racing and in 91% of horses in training. Although exercise is the key factor to ulcer development, the diet and environment also contribute to the risk of ulceration and degree of ulceration. Of all the contributing factors, nutrition and dietary practices are the easiest to adjust within a current training program.
The key influencer in development of gastric ulcers is the intensity and regularity of exercise. Exercise influences gastric volume, increasing exposure of the squamous mucosa to gastric secretions, hydrochloric acid and pepsin. Exposure of the squamous mucosa to gastric acid is thought to be the primary cause of ulcers. Other acids, Volatile Fatty Acids (VFAs) or Short Chain Fatty Acids (SCFAs) from fermentation within the stomach will also contribute, along with possible bile reflux from the small intestine and the influence of pepsin.
With a high bacterial population within the stomach the use of diets high in Non Structural Carbohydrates (NSC) leads to the production of various SCFAs including lactic and acetic acid. These two acids are found in the greatest concentrations in grain fed horses with values reported at >10mmol/L (Al Jassim,2006; Nadeau et al.,2000 cited in Durham 2010).
Studies into the effects of SCFAs and VFAs have shown a connection with ulceration. Nadeau et al.,2003 cited in NRC added 60 nmol/L of VFAs and noted increased tissue damage. Andrews et al.,2006 cited in Durham 2010, studied the influence of SCFAs in vitro concluding at >0.5kg grain/100kg BW horses were at a higher risk of squamous mucosal ulcers. With a common practice of ‘two bowls at night’ with weights ranging from 3-4kg as fed, the grain intake is typically higher than 0.5kg/100kg BW. In line with this finding horses receiving more than 2g of starch /kg BW / meal had double the risk for development of ulcers than horses on lower starch intakes (Luthersson et al.,2009 cited in Durham 2010).
The influence of SCFAs is connected with acidity whereby once the pH is greater than 4.5 the SCFAs have little injurious effect. The reality within training programs where pasture access is frequently limited and forage intake is intermittent, is that pH is often lower than 4.5, with a pH of less than 4.0 being seen when hay consumption is less than 0.3kg in a 4 hour period (Husted et al.,2009 cited in Durham 2010). Typical feeding practices will provide additional forage at evening feed, however this is often consumed within a matter of hours and the stomach will be without forage for significantly more than 4 hours before morning feed, at which point the pH will be such that any SCFA’s produced will promote ulceration.
Even with ad libitum hay the horse will often have a lower pH. Murray & Schusser 1993 (cited in NRC 2007) noted a median pH of 3.1 in horses fed ad libitum grass hay versus horses undergoing feed deprivation with a median pH of 1.6 (24 hour deprivation period). Dried forages will satisfy the appetite and dry matter requirements of the horse much faster than pasture that has a low dry matter content. It is the constant chewing action on pasture that generates high volumes of saliva that act as a natural defence mechanism to gastric acid. The pattern of feeding when stabled is equally as important as what is fed to the horse.
References: Durham,E.(2010) Conditions affecting gastrointestinal health tract health. In A.D.Ellis, A.C.Longland , M.Conen & N.Miraglia (Eds) The impact of nutrition on the health and welfare of horses (pp 145-160) The Netherlands: Wageningen Academic Publishers,National Research Council (2007) Nutrient Requirements of Horses 6th Ed. Washington DC: The National Academic Press.