Equine Gastric Ulcer Syndrome (EGUS)

Over the last decade, studies have increased our awareness and understanding of Equine Gastric Ulcer Syndrome but there is still much to learn. We know there are two distinct diseases which affect different areas of the stomach: Equine Squamous Gastric Disease (ESGD) and Equine Glandular Gastric Disease (EGGD). Whilst a recognised aetiology and recommended management regimes exist for ESGD, less is known about EGGD.

Types and grades of gastric ulcers

As the names suggest, ESGD are ulcers in the squamous region of the stomach and EGGD describes issues in the glandular region of the stomach which researchers now describe as inflammatory disease rather than ulcers. This is an important point to recognise in relation to both risk factors and treatment protocols; the two diseases should be viewed very separately. This distinction is also the reason that whilst a grading system exists for ESGD to define the severity of the ulcers, EGGD is not graded in the same way, if at all. In fact, a recent study showed the current grading system for EGGD had little value due to significant differences in grading by veterinary professionals (Pratt et al, 2022).

Equine Gastric Ulcer Syndrome Grading

The grading system for ESGD is on a 0 to 4 scale with 4 being the most severe. The table below shows the definitions for each grade

Symptoms of gastric ulcers in horses

Symptoms are not always very easy to distinguish from other issues or diseases but some common ones include:

• weight loss
• dull coat
• biting when being girthed
• intermittent colic

The same symptoms can apply to both ESGD and EGGD as they both cause digestive discomfort. It is important to consider that good doers and those that look healthy on the outside can have ulcers too. It is also apparent that there is no link between the severity of ulcers and the symptoms – some horses are clearly very stoic and can have grade 4 ulcers with no obvious clinical signs.

How do I know if my horse has ulcers?

An endoscopic examination aka gastroscopy is the only way to definitively diagnose ulcers but the following symptoms may be indicative of ulcers and mean you should be discussing the situation with your vet:

• Recurrent mild colic that seems to resolve without veterinary intervention
• Reluctance to go forward when ridden particularly if this is not normal for this horse
• Limited appetite
• Starts eating bucket feed and stops
• Poor condition and weight loss
• Starting or worsening of wind-sucking and/or cribbing
• Biting when being girthed

Why do squamous ulcers occur?

The squamous mucosa or tissue is about one-third of the horse’s stomach. It doesn’t have any built-in protection against the acid produced in the glandular region but instead relies on the almost continuous trickle of fibre and saliva entering the stomach to act as a physical barrier to the acidity and to buffer the acidity respectively. This is one of the key reasons why low fibre diets are so detrimental to gastric health. When the horse is exercised the stomach is compressed and if there is little or no fibre present, the acidic juices in the stomach can splash around and are in closer contact with the squamous mucosa. This increases the risk of ulceration occurring. In addition, feeding cereals which are high in starch, increases the level of acidity in the stomach which compounds the problem.

Key Points

• Feeding too little fibre reduces saliva production– chewing fibre produces more than double the amount of saliva compared to chewing concentrates as the horse uses more force through its jaw which is directly correlated with the amount of saliva produced
• Feeding 1% of bodyweight as cereals resulted in a marked increase in ulcers in non-exercised horses – keep the level of cereals in the diet as low as possible to reduce the risk of ulcers
• Feeding 2g/kg of bodyweight starch per day or 1g/kg of bodyweight per meal more than doubled the risk of a horse having ulcers

So if too little forage is a risk factor, how much forage should I feed?

Feeding forage to appetite is the simple answer assuming the horse isn’t overweight. Horses will typically consume between 2 and 2.5% of bodyweight per day as forage when fed to appetite. Ponies may consume more so it is important to watch for weight gain as a result. In fact, the challenge of feeding enough forage to reduce the risk of ulcers without promoting weight gain was a key issue for many of the 650 horse owners that participated in a survey about managing good doers in 2021.

Clearly in many cases we do have to limit our horses’ access to grass to manage their weight and so what do we replace it with to find that balance between reducing ulcer risk but maintaining digestive health? Grass hay or haylage can still be too much for some good doers especially if fed to appetite and so restricting the amount fed is often necessary.

The increasing frequency with which ulcers is being diagnosed may account for why the recommendations for minimal dry matter intake tend to increase in more recent studies. Rendle et al (2020) cite 1.5% of the horse’s bodyweight on a dry matter basis which is the level most equine nutritionists would work to for the long term management of good doers. The veterinary perspective in some cases may be to restrict intake to below 1.5% in the acute scenario to deal with significant obesity, hyperinsulinaemia and acute laminitis but the aim should always be to return to 1.5% of bodyweight for the long term health of the horse. There are other potential health issues aside from EGUS to consider too. It has been shown in trials in mice for example, that a low fibre diet increases the permeability of the gut – a phenomenon known as leaky-gut syndrome. When fibre is fermented in the hind gut, one of the volatile fatty acids produced is butyrate and this is the energy used by the colonocytes (gut cells) themselves. Insufficient fibre and therefore butyrate, can compromise the health of the cells creating bigger gaps between them which allows contents of the gut that shouldn’t pass through, to do so. Therefore, the better strategy for feeding to maintain gut health without promoting excessive weight gain is to feed a lower calorie forage so that more can be fed.

Using straw for horses with ulcers

Back in 2009, a study that looked at the incidence of gastric ulceration in a population of horses found that those that were fed straw as the sole or predominant fibre source were more likely to have ulcers. The reasons given related to the structure of straw and the fact that straw contains low levels of calcium and protein. This makes sense given that it is alfalfa’s naturally high protein and calcium levels that are thought to make it a superior buffer.

However, the key here is that straw was used as the sole or predominant fibre source which is not typically done in the UK. Recognising that straw can be useful as a low-calorie forage source for good doers, a follow up study has been published investigating the safety of feeding 50% wheat straw to replace haylage. This study by Jansson et al (2021) found no ill effects and specifically looked for gastric ulcers. Some simple calculations show that if straw replaces 1/3 of the weight of an average hay, a reduction in energy intake of 16% is achieved. Obviously replacing half the haylage ration will achieve an even greater reduction.

Forages for horses that aren’t good doers

The more stereotypical horse with ulcers is one that doesn’t hold weight and looks in poor condition. In these scenarios the key challenge is promoting weight gain without increasing starch intake. The first step to achieving this is to use as digestible a form of forage as possible and feed plenty of it.

Can I use haylage for a horse with ulcers?

The concern about using a true haylage for horses with ulcers is that the fermentation process used to conserve the forage produces acids and feeding a forage with increased acidity levels would not be helpful in trying to manage EGUS. However, a more accurate description of many so-called haylages would be ‘wrapped hay’ as they are often very dry which has meant that little or no fermentation has occurred. This means the levels of acidity are no different to a normal hay which can be seen in table 2. A possible benefit of using wrapped hay is that it may well have been harvested earlier and so is likely to be more digestible meaning that the horse is likely to do better on it. Forages containing more moisture and cut earlier are often more palatable which is useful for poorer doers who may not have a big appetite. For poor doers, feeding forage to appetite is ideal as there is no reason to restrict them.

Table 2 – A comparison of different forages (data from Dengie analysis records and Muller and Uden (2007))

EGGD aetiology

The glandular region of the stomach contains glands that secrete hydrochloric acid, pepsin, bicarbonate and mucus. The stomach secretes acid continuously; as the horse is a trickle feeder it needs to continuously produce digestive compounds and it is important to note that this process continues even when the horse isn’t eating. The volume of secretion has been shown to be around 1.5l of gastric juice per hour although this does vary at different times during the day. The pH of the stomach contents ranges from 1.5 to 7 depending on location with the area at the oesophagus around 7 (neutral), which decreases to between 3 to 6 around the margo plicatus which is where the stomach tissue type changes and then down to 1.5 to 4 in the glandular region. Remember that a lower pH means the stomach is more acidic and so a pH below 4 in the squamous region contributes to an increased risk of ulceration occurring.

Risk factors for EGGD

A great review has been written by leading veterinary researcher Mike Hewetson of the RVC – click here to read it. Some key takeaways from this review are:

• Even if a horse has both ESGD and EGGD it doesn’t mean they are associated
• EGGD is likely to result from the breakdown of normal defence mechanisms that protect the stomach tissue ie the secretion of mucus.
• An increasing amount of evidence exists to suggest an association between stress and EGGD
• In Thoroughbred racehorses, the trainer has been identified to be a risk factor independent of other management factors
• EGGD was inversely correlated to the experience of the horse in both polo ponies and show jumpers which may suggest a degree of adaptation to physiological stress, differences in management of elite horses or selection for horses that do not develop EGGD.
• Exercise is also a risk factor – exercising more than 4 or 5 days per week was found to be a risk factor for EGGD in racing Thoroughbreds and showjumpers respectively
• In endurance horses, the prevalence of EGGD doubled during the competition season compared with the inter-season period

The link between stress and the incidence of EGGD is one reason why the problem is difficult to resolve. Removing the cause of stress can be difficult for performance horses as stress is inherent in their role, owners and trainers can therefore face difficult choices if EGGD persists.

Managing a horse with EGGD

Whilst there is no evidence-based link between diet and EGGD, the advice is still to implement the same feeding management as for ESGD which amounts to reducing starch intake and feeding plenty of fibre. More crucially, trying to minimise stress by ensuring continuity of carer and reviewing any practices on the yard that may be distressing the horse are key. Providing at least 2 rest days a week are also recommend.

Should my ulcer prone horse have a bucket feed?

UK pastures and forages produced from them, lack a number of key trace minerals including zinc, copper and selenium and so even horses and ponies at rest or in light work, benefit from a source of these essential nutrients. They are important for many different functions such as energy breakdown and utilisation and as part of the body’s antioxidant defence system. Topping up these nutrients by adding a broad-spectrum vitamin and mineral supplement or balancer helps to ensure a balanced diet is supplied.

Feeding a double handful of a chopped fibre feed in the 20-25 minutes before exercising is also recommended to help prevent ‘acid splash’ in the squamous region of the horse’s stomach. The fibre ensures the stomach isn’t empty and suppresses the movement of the acidic contents when the horse moves. If a horse has been eating grass or forage then this performs the same function.

For poorer doers and those in harder levels of work, forage may not be sufficient to keep them in an acceptable condition and so the bucket feed is an important part of the ration. There are a range of feeds with the BETA approval mark for horses and ponies prone to EGUS which range in ingredients and type. This is an independent assessment of the suitability of a product for those prone to EGUS. Part of the approval process involves the Veterinary Medicines Directorate – a government agency responsible for ensuring medicines are safe and efficacious as well as ensuring false claims aren’t attributed to products such as feeds and supplements. Choosing an approved product means you can be sure companies are not making claims about products they can’t substantiate.

What ingredients are good for horses with ulcers?

The most important requirement is that an ingredient should be low in starch. This tends to mean that ingredients high in fibre and/or oil are most popularly used. There are published studies to support the use of ingredients such as alfalfa and sugar beet for horses with ulcers. Studies back in the early 2000s (Nadeau et al, 2000; Lybbert et al, 2007) showed that alfalfa was more beneficial for horses with ulcers (ESGD) compared to grass forages, as the high levels of calcium and magnesium it contains act as natural buffers to acidity. More recently studies carried out by the Lab to Field research group based in Dijon, France have shown the protective effects of alfalfa in horses in training. Their findings demonstrated that clinical success with horses with EGGD was 47.7 times more likely in horses fed alfalfa pellets as part of their ration compared to those on concentrate only rations.

A study published in 2024 showed that a combination of alfalfa, sugar beet and oat fibre aided reduction in recurrence of gastric ulcers when fed during the healing and post-medication periods in addition to the usual ration. This is key for when ulcer medication is stopped and the rebound increase in acid production can occur (Menzies-Gow and Shurlock, 2024).

Why does alfalfa contain more calcium than grass forages?

Alfalfa has really deep roots – about 3 to 4 metres – and the calcium at this depth in the soil is more available for absorption. This means that alfalfa plants can take up more calcium than grass – chopped alfalfa contains between 30 and 50% more calcium than grass forages. Early studies suggest that omeprazole is reducing calcium absorption in the horse as is seen in humans and in Swanhall et al’s (2018) study, they recommend using bio-available calcium sources in the diet to help counteract this effect. Plant based sources of calcium such as alfalfa are much easier for the horse to absorb than inorganic sources such as limestone flour.

How much alfalfa should be fed?

Researchers suggest adding around 200grams, which is about half a Stubbs scoop, when cereals are fed to help counteract the increases in acidity generated by the starch.  In many cases, high quality fibre sources can be used to provide the horse with sufficient energy for the work they are doing reducing the need to feed cereals and thereby reducing starch intake. This has been demonstrated in a recent study by Martin et al (2023) who showed that horses in training fed a third of their total ration as alfalfa with just 7% oats performed comparably with those fed 33% oats (the remainder of the diet was hay). The replacement of oats with alfalfa had no detrimental effects on performance or muscle tone and in fact, altered energy metabolism in such a way as to potentially improve performance and recovery.

Why is alfalfa so low in starch?

Like other plants alfalfa makes sugar when photosynthesising but it stores any surplus sugar as starch in its roots – the part that horses don’t eat! Grass plants tend to store sugar as fructan in leaves and the stem which is why they supply the horse with more sugar.

So why are some people concerned about feeding alfalfa?

There has been a study published that has caused confusion about the use of alfalfa. It explored the incidence of ulcers in foals and used the weaning process to induce ulcers. The researchers then compared groups fed alfalfa chaff or alfalfa pellets or hay. Foals were fed 3kgs (7.5 Stubbs scoops) of alfalfa chaff (way more than is typically used or what would typically be recommended for foals), 2.7kgs of oats and 0.25kgs of soybean meal. It’s also important to note that the alfalfa chaff used was 40% lower in calcium than the alfalfa pellets used. Evidence of EGGD was found in foals fed alfalfa chaff but not in those fed alfalfa pellets or hay but none showed any clinical signs. It is important to reiterate the link between stress and EGGD; those foals might well have had EGGD regardless of what they were fed – as evidence from other studies suggests. The same research group have recently published another study comparing grass and alfalfa hay in adult horses and found no issues with feeding alfalfa (Bauerlein et al, 2020)

So what can we conclude?

• There have been no negative effects in the squamous region of the stomach in horses of any age from feeding alfalfa
• The only group where an effect with alfalfa chaff has been seen is weaned foals but it was fed at much higher levels than is typically done – there were no issues associated with feeding alfalfa pellets which would still provide some natural buffering from the calcium they contain
• Alfalfa chaff or chop is widely considered beneficial for adult horses at risk of or prone to EGUS due to its natural buffering potential

Summary

• ESGD and EGGD are very different diseases and even when concurrent may not be related
• ESGD risk factors are well established and include too little fibre, too much starch and exercising on an empty stomach
• Feeding at least 1.5% of bodyweight on a dry matter basis is the minimum amount of forage required for long term gastric and digestive health
• Feed a lower nutritional value forage so you can feed 1.5% of bodyweight without resulting in excessive weight gain
• Straw is a safe ingredient to use at up to 50% of the forage ration
• Wrapped hays that have not fermented and so are no more acidic than hay are also appropriate to use for horses with ulcers
• EGGD is still not fully understood but increasingly it is acknowledged by researchers that stress is a key contributing factor
• Alfalfa is safe to use for all horses with ESGD and adult horses with EGGD. One study suggests a possible increase risk for foals who were fed much bigger amounts than is typically done – if concerned use alfalfa pellets for their natural buffering benefits
• Studies have shown alfalfa to be beneficial as an alternative energy source compared to cereals for horses in training

References

• Bauerlein et al (2020) Effects of feeding alfalfa hay in comparison to meadow hay on the gastric mucosa in adult Warmblood horses. Pferdeheilkunde – Equine Medicine 36.
• Dugdale et al (2010) Effect of dietary restriction on body condition, composition and welfare of overweight and obese pony mares. Equine Veterinary Journal, 42 (7) 600-610.
• Jansson et al (2021) Straw as an Alternative to Grass Forage in Horses—Effects on Post-Prandial Metabolic Profile, Energy Intake, Behaviour and Gastric Ulceration. Animals. 11.
• Julliand et al (2023) Effect of diet composition on glandular gastric disease in horses. Journal of Veterinary Internal Medicine
• Lybbert et al (2007), Proceedings of Annual Convention of the AAEP, Orlando, Florida, 2007.
• Martin et al (2023) Effect of high-starch or high-fibre diets on the energy metabolism and physical performance of horses during an 8-week training period. Front. Physiol. 14:1213032. doi: 10.3389/fphys.2023.1213032
• Menzies-Gow and Shurlock (2024) The effect of feeding a commercial feedstuff on equine gastric squamous disease. Journal of Equine Veterinary Science. 133.
• Morgan et al (2016) Treatment of Equine Metabolic Syndrome: A clinical case series. Equine Veterinary Journal. 48. 422-426.
• Nadeau et al (2000) Evaluation of diet as a cause of gastric ulcers in horses. American Journal of Veterinary Research. Jul;61(7):784-90.
• Pratt et al, (2022) Assessment of agreement using the equine glandular gastric disease grading system in 84 cases. Veterinary Medicine Science, 8 (4) 1472-1477doi: 10.1002/vms3.807
• Rendle et al (2020) Tackling obesity and related laminitis in equine patients. Veterinary Times Equine, 6 (1) 6-9.
• Swanhall et al (2018) Mineral and Vitamin Supplementation Including Marine Derived Calcium Increases Bone Density in Thoroughbreds. Proceedings of the Australasian Equine Science Symposium