The incidences and severity of cases of Equine Gastric Ulcer Syndrome (EGUS) are sadly, on the increase. Indeed, some recent studies suggest that approximately 93% of Thoroughbred, racehorses and endurance horses suffer from ulcers.
Starting with the gastro-intestinal tract
The horse, as a non-ruminant herbivore, is well suited to a high fibre, low starch diet, and would, in it’s natural environment, spend 18 hours a day foraging, rarely fasting for more than 2 – 4 hours at a time. Saliva is generated in response to chewing and, in a natural grazing environment this helps to buffer gastric acid, which is secreted continuously into the stomach. In addition, natural living conditions encourage the horse to move freely, which is believed to assist with the normal movement of stomach contents through the gastrointestinal tract.
Modern management practices, such as feeding meals often in an enclosed environment with limited opportunity for free movement, low fibre / high concentrate (starch) laden rations, early weaning and intensive training programmes are believed to contribute to producing poorly buffered, acidic conditions in the stomach (Davidson and Harris, 2002, Andrews et al., 2006). This is thought to be associated with the high prevalence of gastrointestinal ulcers, particularly in intensively managed horses.
Up until now, much of our diagnosis and traditional nutritional management of EGUS has concentrated on the upper, ‘squamous’ part of the horse’s stomach. Equines with ulcers present in this region are referred to as having, ‘Equine Squamous Gastric Disease’, ESGD; whilst equines with ulcers present in lower, ‘glandular’ section of the stomach constitute a distinct and different disease – ‘Equine Glandular Gastric Disease’, EGGD (Sykes et al., 2015a).
It’s important to draw a distinction between the two diseases as management of them differs. Indeed, the nutritional strategies that we use for managing ESGD, such as ensuring ad-lib access to a high-fibre diet and reducing the amount of starch content levels in the ration, will not necessarily improve and reduce EGGD.
A number of contributory factors
It is widely accepted that all gastric ulcers occur when there is an imbalance between those factors that are protective to the gastric mucosa (such as mucus, bicarbonate, prostaglandins, mucosal blood flow and the epithelial restitution) and those that are ulcerogenic (including the presence of hydrochloric acid, volatile fatty acids (VFA), pepsin or bile acids) (Ethell et al., 2000; Lester, 2004). There are a number of contributing factors that are thought to affect this balance.
The amount of starch fed per day, and per meal, in particular, is a very important factor. There have been numerous studies showing the development of EGUS when equines are fed high starch content diets (Frank et al., 2006)
Nadeau et al., 2000, demonstrated that high starch diets tend to result in higher VFA production in the upper layers of the gastric mat and possibly higher lactic acid production in the lower layers due to failure of the gastric acid to penetrate the less moist bolus and stop rapid fermentation from occurring (Harris et al., 2006).
High starch diets tend to reflect a high cereal intake, which can also promote acid splashing (Argenzio, 1999, Lorenzo-Figueras and Merritt, 2002); in addition, cereals tend to be low in calcium and possibly, other buffering agents that might also lead to the increased risk.
It is widely accepted therefore, that reducing the amount of starch given each day as well as the amount provided in each meal, may reduce the likelihood of EGUS (Luthersson et al., 2009).
2. Feeding Straw as the only forage provided
Luthersson et al., 2009 also concluded that there was an increased likelihood of EGUS formation when straw was the only forage provided for horses.
Straw is low in protein and calcium and is thought not to provide buffering support. It can also be highly lignified and there is the potential therefore, that if not properly chewed, some irritation of the gastric mucosa could result from high levels of intake. It is also possible that the high lignin and silica nature of straw alters the fibrous mat in some way to increase the risk of the squamous epithelium being exposed to acidogenic factors (Luthersson et al., 2009).
3. Deprivation of food and water
Deprivation of food for repeated periods has been shown to cause gastric ulcers in the squamous non-glandular region (ESGD), but not the glandular region (Murray and Grady, 2002). Feed deprivation is associated with highly acidic conditions in the stomach and the more liquid, less saliva buffered contents may be easily displaced or ‘splashed’.
In addition, Luthersson et al., 2009 demonstrated that horses without access to water were more likely to have both EGUS and non-glandular ulcers (ESGD).
Transportation has been associated with an increased risk of EGUS (McClure et al., 2005) and may be associated with disturbances in feed as well as water intake. Water intake may result in dilution of gastric fluid (Andrews et al., 2006) and therefore, pH, although the passage of water through the stomach may depend on the nature of the gastric contents.
Several studies have demonstrated potential associations between EGUS and level of exercise (Murray et al., 1996, Orsini, 2000, Lester, 2004, Chameroy et al., 2006, Jonsson and Egenvall, 2006).
With squamous disease (ESGD), during a horse’s exercise, acid splashes up onto the squamous mucosa, so the longer spent exercising, the more damage that will be done. It is a cumulative effect, so that over a period of time, the amount of exercise done, at trot or above, will contribute to the risk of squamous disease.
For glandular disease (EGGD), although the risk factor is exercise, it’s the number of days spent exercising that matter. In one study, show-jumping horses exercised six or seven times a week were found to be approximately three and a half times more likely to develop glandular disease than those exercising five days or less. Similar research focusing on racehorses who were exercised five days or more, versus those working four days or less, showed a ten-fold increase in the risk of glandular disease. Rest days are therefore vitally important when managing EGGD.
Stress isn’t directly associated with squamous ulcers (ESGD), but it is with glandular (EGGD). Indeed, we know that equines with glandular ulcers have a more pronounced response to stress testing, so effective management of the condition, involves giving them rest days as well as trying to reduce their daily stress levels.
In conclusion, we know that certain factors can contribute to all gastric ulcer formation. In particular, reducing the total amount of starch fed each day, as well as the amount provided in each meal may significantly reduce EGUS prevalence. Ensuring that water and food is available, and that straw is not the only form of forage provided, is also advisable. Finally, avoiding leaving horses without forage provision for more than 6 hours should be avoided (Luthersson et al., 2009); as well as reducing stressful and over-strenuous exercise schedules.
However, it’s important to know which type of ulcers that your horse has, in order to manage the condition appropriately. Whilst squamous ulcers (ESGD), are undoubtedly, the most prevalent - the incidences of glandular ulcers (ESGD), are increasing. One recent report estimates that 30 – 50% of the domestic horse population are suffering with glandular ulcers, with environmentally stressed horses at high risk, even if they are in low-level work.