The art and science of feeding horses prone to gastric ulcers

Words - Sarah Nelson

Risk factors for squamous or ‘non-glandular’ ulcers are well documented and include low forage diets and long periods without eating, diets high in non-structural carbohydrate (NSC) or ‘starch and sugar’, intensive exercise and stress, as well as prolonged periods of stabling and travelling. While some risks may be unavoidable for racehorses in training, diet is one that can be influenced relatively easily. 

In this article, Nutritionist, Sarah Nelson, discusses some of the science and provides practical advice on the nutritional management of horses prone to non-glandular ulcers. While glandular ulcers may be less responsive to changes in diet, the same nutritional management is generally recommended for both glandular and non-glandular ulcers. 

Evidence that diet makes a difference

Research published by Luthersson et al (2019) was the first to show that changes in diet can reduce the recurrence of non-glandular ulcers following veterinary treatment. In this 10-week trial, fifty-eight race/ competition horses were paired according to their workload, management and gastric ulcer score (non-glandular ulcers graded 0-4). One horse from each pair continued with their normal diet while the other had their normal ‘hard feed’ replaced with the trial diet which was divided into three equal meals. Horses with grade 3 and grade 4 ulcers were also treated with the recommended dose of omeprazole for four weeks. All horses were scoped at the start of the trial, immediately after omeprazole treatment had finished and 6 weeks after treatment had stopped. 

The majority of horses improved as a result of omeprazole treatment regardless of diet. Diet had no effect on grade 2 ulcers. At the end of the study, gastric ulcer scores in the horses that were fed the trial diet were not significantly better or worse than in horses that were not fed the trial diet. Overall, gastric ulcer scores in horses that were fed the trial diet remained improved 6 weeks after treatment had stopped. Six weeks after treatment had stopped, gastric ulcers scores had worsened in the majority of horses that remained on their normal feed so that overall, there was no difference between pre and post treatment scores.  

Importantly, this research shows that changes in diet can help to reduce the risk of gastric ulcers recurring after treatment, even if other changes in management are not possible. There was also no apparent long-term benefit of omeprazole treatment alone, highlighting the importance of other strategies in the long-term management of horses prone to gastric ulcers.  As this study only evaluated changes in ‘hard feed’, it is possible that greater improvements could have been achieved if changes to forage were also made. 

Recent research reveals unexpected results

Regular turnout often isn’t possible for horses in training and while the risk of gastric ulcers generally seems lower in horses at pasture, recent research carried out in Iceland by Luthersson et al (2022) has highlighted this may not always be the case.

In Iceland, horses typically live out at pasture, often in large herds and if stabled, they are generally fed a high forage, low starch and low sugar diet. While Icelandic horses do get gastric ulcers, it’s been suggested that the over-all incidence is low. 

The aim of this study was to investigate the incidence of gastric ulcers in Icelandic horses moving from pasture into light work. Prior to the study, all horses had lived out in large herds for their entire adult lives (age range 3-7 years), had never been in work and were fed supplementary forage in winter months only. All horses were scoped within two weeks of being removed from pasture (prior to starting ‘training’) and were scoped again approximately after 8 weeks of being stabled and doing light work. Most horses were fed forage only during the training period, but 11 were given very small amounts of soaked sugar beet and 3 were given a small amount of commercially produced feed. However, in all cases, starch and sugar intake from ‘hard feed’ was equivalent to less 250g per meal for a 500kg horse which is well within the current recommendations for horses prone to gastric ulcers.

Approximately 72% of horses had non-glandular ulcers (grade 2 or above) at scope 1. The prevalence and severity of gastric ulcers improved after eight weeks of stabling and light work - approximately 25% of horses had non-glandular ulcers (grade 2 or above) at scope 2. Horses given forage three times per day as opposed to twice per day were almost 18 times more likely to improve! Over-all, the incidence of glandular ulcers decreased from 47% to approximately 41% 

The high prevalence and severity of non-glandular ulcers at the start of the study, and the subsequent improvement following the training period was unexpected. Not only is this research an important reminder that horses at pasture are still at risk of gastric ulcers, it highlights the importance of regular forage provision. 

Forage focus

Forage is critical for mental wellbeing and digestive health in all horses but sometimes receives less attention than ‘hard/ concentrate’ feed, particularly for performance horses. When it comes to reducing the risk of gastric ulcers, one of the main benefits is promoting chewing. 

Saliva provides a natural buffer to stomach acid but unlike people, horses only produce saliva when they chew, which is why long periods without eating increase stomach acidity. In one study, the risk of non-glandular ulcers was found to be approximately 4 times higher in horses left for more than 6 hours without forage, although the risk may be greater during the day. 

Research by Husted et al (2009) found gastric pH drops in the early hours of the morning, even in horses with free access to forage. Not only do horses generally stop eating/ grazing for a period of time during the early hours of the morning, they are normally less active at night, reducing the risk of gastric splashing.

It should also be remembered that forage is a source of fuel – even average hay fed at the minimum recommended amount may provide close to 45% of the published energy requirement for a horse in heavy exercise. Forage analysis can be a useful tool, especially if you can source a consistent supply. 

Routine analysis normally includes measuring / calculating the water, energy and protein content, as well as providing an indication of how digestible the fibre is - more digestible forages yield greater amounts of energy and can help to reduce the reliance on feed.

Minimum forage intake

Ideally all horses, including racehorses in training should be provided with as much forage as they will eat. However large amounts of bucket feed, intense training and stress can affect appetite so voluntary intake (how much is eaten) should be monitored wherever possible. 

In practice, this means weighing the amount of forage that’s provided, as well as any that is left in a 24-hour period.  Ideally, total daily forage intake should not be restricted to less than 1.5% bodyweight per day on a dry matter basis, although an absolute minimum of 1.25% bodyweight (dry matter) is considered acceptable for performance horses, including racehorses in heavy training. 

On an ‘as fed basis’ (the amount of forage you need to weigh out), this typically equates to (for a 500kg horse without grazing):

• 9kg of hay if it is to be fed dry or steamed (or an absolute minimum of 7.5kg)

• 11-12kg* of haylage (or an absolute minimum of 9-11kg*)

The difference in feeding rates can cause confusion but essentially, even unsoaked hay contains some water and the water doesn’t count towards the horse’s forage intake. 

*based on a dry matter of 65-70%

How much starch and sugar is ‘too much’?

The fermentation of starch by bacteria in the stomach results in the production of volatile fatty acids which in conjunction with a low pH (acidic environment), increases the risk of ulcers forming. Current advice, which is based on published research, is to restrict non-structural carbohydrate (NSC) or ‘starch and sugar’ intake from ‘bucket feed’ to less than 1g per kilogram of bodyweight per meal and ideally less than 2g per kilogram of bodyweight per day. For a 500kg horse, this is equivalent to:

• Less than 500g per meal 

• Ideally less than 1kg per day

Traditional racing feeds are based on whole cereal grains and as a result, are high in starch. By utilising oil and sources of highly digestible fibre such as sugar beet and soya hulls, feed manufacturers can reduce the reliance on cereal starch without compromising energy delivery. 

Meal size matters

There are several reasons why horses should be fed small meals but one that’s of particular importance to managing the risk of gastric ulcers is reducing the amount of starch and sugar consumed in each meal. 

Large meals may also delay gastric emptying and in turn, lead to increased fermentation of starch in the stomach, especially if cereal based. Restrict total feed intake to a maximum of 2kg per meal which is equivalent to approximately 1 Stubbs scoop of cubes.  

Feeding ‘chaff’ to prevent gastric splashing

The horse’s stomach produces acid continuously (although at variable rate). Exercise increases abdominal pressure, causing acid to ‘splash’ onto the stomach lining in the non-glandular region where it increases the risk of ulcers forming. Exercise may also increase acid production.

Feeding short chopped fibre helps to prevent ‘gastric splashing’ by forming a protective ‘fibre mat’ on top of the contents of the stomach and may be of increased benefit to horses on restricted forage diets. Current advice is to feed 2 litres of short chopped fibre volume – equivalent to 1 Stubbs scoop – within the 30 minutes prior to exercise. Ideally choose a fibre containing alfalfa as the high protein and calcium content is thought to help buffer acid.

Supplements safety & efficacy

Supplements are often an attractive option, with owners and trainers from various disciplines reporting benefits. Unfortunately, scientific evidence is currently limited with some studies producing conflicting results which means specific recommendations regarding the optimum blend of ingredients and recommended daily intakes have not been established. 

However, ‘ingredients’ that may help to support gastric health include pectin and lecithin, omega 3 fatty acids, fenugreek, threonine, liquorice and maerl, a marine derived source of bioavailable calcium. But don’t forget, there are some important safety considerations, both for horse health and mitigating the risk of prohibited substances. 

• Supplements should never be used as an alternative to veterinary treatment or an appropriate diet.

• Beware of bold claims – if it sounds too good to be true it probably is!

• It is illegal for manufacturers to claim products can cure, prevent or treat gastric ulcers. Words like ‘soothe’ and ‘improve’ are also prohibited. While bold or illegal claims do not automatically mean a supplement presents are unsafe, it does raise questions over the company’s ethics. 

• Speak to a nutrition advisor before feeding supplements containing added vitamins and minerals as some can be harmful (or even toxic) if oversupplied.

• Avoid supplements (and feeds) containing added iron.

• Be cautious of supplements containing iodine, including naturally occurring sources such as seaweed.

• Ensure the total diet provides no more than 1mg selenium per 100kg bodyweight (5mg per day for a 500kg horse).

• Natural does not always equal safe – avoid herbs of unknown origin.

• In the UK, use only BETA® NOPS (British Equestrian Trade Association, Naturally Occurring Prohibited Substances) approved feeds and supplements.

• Only use supplements produced by an authorised feed manufacturer (supplements are classified as feeds in the UK and the EU and regulated by the same legislation). Approval numbers must be included on the label but knowing what to look out for can be tricky. That said, any supplement carrying the BETA® EGUS approval mark will have been produced by an authorised manufacturer.

The BETA EGUS approval mark 

Although they are by no means the only suitable option, you can be assured that feeds carrying the BETA® EGUS approval mark have been through a rigorous independent review process to ensure:

• The combined starch and sugar content is less than 25% for high energy feeds and less than 20% for low-medium energy feeds

• They provide less than 1g of starch and sugar (combined) per kilogram bodyweight per meal when fed as recommended

• No inaccurate or medicinal claims are made on the packaging or in marketing materials

• The feed is correctly labelled

• It fulfils the nutrient specification – this includes independent laboratory analysis

Full references for scientific research available on request.

Nutrition and the new science of the "Gut-Brain connection"

Article by Scott Anderson

Trainers are always looking to gain an edge in performance. But what about their mental state? Are they jittery, distracted or disinterested? No matter how strong the horses, their heads must be in the game to succeed.

Surprisingly, much of that mental attitude is driven by gut health, which in turn depends on the collection of microbes that live there: the microbiota. In a horse, the microbiota is a tightly packed community of about 100 trillion microbes, composed of bacteria, archaea, fungi and protozoa. It colonises the entire GI tract but is largely concentrated in the hindgut, where it works to ferment the prebiotic fibre in forage. The microbial fermentation of fibre into fatty acids produces 70% of the animal’s energy requirements and without it, the horse couldn’t get sufficient energy from simple forage. Intriguingly, byproducts of that fermentation can affect the brain. 

It is easy to be sceptical about this gut-brain connection, but over the last decade, research has made it clear that gut microbes have an outsized influence on mood and behaviour. Microbes that improve mental state are called psychobiotics, and they may completely change the way you train and manage your horses. A horse’s health – and consequently its performance – starts in the gut.

Inflammation

When the microbiota is unbalanced by stress, diet or sickness, it is said to be dysbiotic. It loses diversity, and a handful of bacterial species compete for domination. Without the pushback of a diverse population, even beneficial bacteria can become pathogenic. Surprisingly, that can affect the brain. Multiple studies in various animal models have shown that transmitting faecal matter from one animal to another also transmits their mood. This demonstrates that a dysbiotic microbiota can reliably cause mental issues including anxiety and depression, thereby affecting performance. 

An important function of the microbiota is to fight off pathogens by outcompeting, starving or killing them. However, a dysbiotic microbiota is less diligent and may permit pathogens to damage the gut lining. A degraded gut lining can leak, allowing bacteria and toxins into the bloodstream. The heart then unwittingly pumps them to every organ in the body, including the brain. This makes the gut the primary source of infection in the body, which explains why 80% of the immune system is located around the intestines. Over time, a leaky gut can lead to chronic systemic inflammation, which weakens the blood-brain barrier and interferes with memory, cognition and mood. 

Inflammation is a major component of the gut-brain connection, but not the only one.

Neurotransmitters and hormones

Horses and humans use neurotransmitters to communicate between nerve cells. Brains and their attendant nerve bundles constitute a sophisticated network, which makes it somewhat alarming that microbes also produce neurotransmitters. Microbes use neurotransmitters to converse with each other, but also to converse with their host. The entire gut is enmeshed in nerve cells that are gathered up into the vagus nerve that travels to the brain. Microbial neurotransmitters including serotonin and dopamine thus allow certain microbes to communicate directly with the brain via the vagus nerve. We know this happens with specific bacteria, including Lactobacillus species, because when the vagus is severed, their psychobiotic effects disappear. 

As well as neurotransmitters, hormones are involved in gut-brain communications. The hypothalamus-pituitary-adrenal (HPA) axis controls the stress response in animals. The hypothalamus is located low in the brain and responds to stressors – such as a lurking predator – by producing hormones that stimulate the neighbouring pituitary, which then triggers the adrenal gland to produce cortisol, the stress hormone. Cortisol acts as a threat warning and causes the horse to ramp up glucose production, supplying the energy needed to escape a predator. This is the same hormonal circuit that trainers exploit for racing.

The HPA axis produces cortisol in response to stress. Cortisol inhibits the immune system, which in combination with a leaky gut allows pathogens to enter the bloodstream. Susequent systemic inflammation and vagal feedback lead to stereotypies.

The production of these hormones redirects energy to the heart, lungs and muscles at the expense of the immune system. From an evolutionary point of view, the tradeoff makes sense: first escape the predator and deal with infections later. After the danger has passed, cortisol causes the HPA to return to normal – the calm after the storm. 

However, continued stress disrupts that cycle, causing anxiety and diminishing the brain’s ability to store memories. This can dramatically interfere with training. Stress can also induce the release of norepinephrine, which promotes the growth of pathogenic bacteria including Campylobacter jejuni, Listeria, Helicobacter pylori, and Salmonella. Prolonged high cortisol levels can increase gut leakiness, potentially leading to infection and further compounding the situation. In the long term, continued stress leads to systemic inflammation, which is a precursor to problematic behaviours.

Short-chain fatty acids

When microbes consume proteins and fibre, they break them down into their constituent molecules, such as amino acids, fatty acids and sugars. These are the metabolites of the microbes. As well as neurotransmitters and hormones, the gut-brain conversation is mediated by metabolites like butyrate, an important short-chain fatty acid which plays multiple roles in the body. 

In the gut, butyrate serves as a preferred nutrient for the cell lining. It encourages the differentiation of stem cells to replenish gut cells that are routinely sloughed off or damaged. It plays an important role in the production of mucus – an essential part of gut protection – which coats the gut from mouth to anus. In the muscles, butyrate boosts the growth of skeletal muscle, crucial to athletic performance, as well as inducing the production of glucose, the primary muscle fuel. One-quarter of systemic glucose is driven by butyrate. In its gut-brain role, butyrate passes through the blood-brain barrier, where it nourishes and enhances the growth of new brain cells. 

These factors make butyrate a star player in the gut-brain connection. They also highlight the benefits of prebiotic fibre, especially when high-energy, low-fibre feeds are provided.

Starting a microbiota

We’ve explored the major pathways of the gut-brain connection: inflammation, neurotransmitters, hormones and fatty acids. Some of these pathways are at odds with each other. How does such a complicated system come together?

As mentioned, the microbiota is an animal’s first line of defence against pathogens, attacking and killing them often before the immune system is even aware of them. That means a healthy microbiota is an essential part of the immune system. However, the immune system is designed to attack foreign cells, which includes bacteria. For the microbiota to survive, the immune system must therefore learn to accept beneficial microbes. This lesson in tolerance needs to take place early in the foal’s development, or its immune system may forever fight its microbiota.

There are multiple ways nature ensures that foals get a good start on a microbiota that can peacefully coexist with the immune system. The first contribution to a protective microbiota comes from vaginal secretions that coat the foal during birth. After birth, microbes are included in the mare’s milk. These microbes are specially curated from the mare’s gut and transported to the milk glands by the lymphatic system. Mare’s milk also includes immune factors including immunoglobulins that help the foal to distinguish between microbial friends and foes. An additional way to enhance the microbiota is through coprophagia, the consumption of manure. Far from an aberration, foals eat their mother’s manure to buttress their microbiota. 

Microbes affect the growth and shape of neurons in various brain sites as the foal develops – a remarkable illustration of the importance of a healthy early gut microbiota. 

The cooperation between the immune system and the microbiota is inevitably complex. Certain commensal bacteria, including Clostridiales and Verrucomicrobia, may be able to pacify the immune system, thus inhibiting inflammation. This is a case where microbes manage the immune system, not the other way around. These convoluted immune-microbial interactions affect the mental state – and consequently the behaviour – of the horse, starting at birth.

Stereotypies

A 2020 study of 185 performance horses conducted by French researchers Léa Lansade and Núria Mach found that the microbiota, via the gut-brain connection, is more important to performance than genetics. They found that microbial differences contributed significantly to behavioural traits, both good and bad. A diversified and resilient microbiota can help horses better handle stressors including stalling, training, and trailering. A weakened or dysbiotic microbiota contributes to bad behaviours (stereotypies) and poor performance. 

The horses in this study were all carefully managed performance horses, yet the rates of stereotypies were surprisingly high. A kind of anxiety called hypervigilance was observed in three-quarters of the horses, and almost half displayed aggressive behaviour like kicking or biting. 

The study found that oral stereotypies like biting and cribbing were positively correlated with Acinetobacter and Solibacillus bacteria and negatively correlated with Cellulosilyticum and Terrisporobacter. Aggressive behaviour was positively correlated with Pseudomonas and negatively correlated with Anaeroplasma. 

Some of these behaviours can be corrected by certain Lactobacillus and Bacteroides species, making them psychobiotics. That these personality traits are correlated to gut microbes is truly remarkable. 

Intriguingly, the breed of a horse has very little impact on the makeup of its microbiota. Instead, the main contributor to the composition of the microbiota is diet. Feeding and supplements are thus key drivers of the horse’s mental state and performance. 

The gut-brain connection and training

How might the gut-brain connection affect your training practices? Here are some of the unexpected areas where the gut affects the brain and vice-versa:

High-energy feed. Horses evolved to subsist on low-energy, high-fibre forage and thus have the appropriate gut microbes to deal with it. A high-energy diet is absorbed quickly in the gut and can lead to a bloom in lactic acid-producing bacteria, which can negatively impact the colonic microbiota. High-energy feeds are designed to improve athletic output, but over time, too much grain can make a horse antisocial, anxious and easily spooked. This can damage performance—the very thing it is trying to enhance. Supplementary prebiotics may help to rebalance the microbiota on a high-starch regimen.

Changing feed regimens quickly. When you change feed, certain microbes will benefit, and others will suffer. If you do this too quickly, the microbiota can become unbalanced or dysbiotic. Slowly introducing new feeds helps to prevent overgrowth and allows a balanced collection of microbes to acclimate to a new regimen. 

Stress. Training, travelling and racing all contribute to stress in the horse. A balanced microbiota is resilient and can tolerate moderate amounts of stress. However, excessive stress can lead, via the HPA axis, to a leaky gut. Over time, it can result in systemic inflammation, stereotypies and poor performance.

Overuse of antibiotics. Antibiotics are lifesavers but are not without side effects. Oral antibiotics can kill beneficial gut microbes. This can lead to diarrhoea, adversely affecting performance. The effects of antibiotics on the microbiota can last for weeks and may contribute to depression and anxiety. 

Exercise and training. Exercise has a beneficial effect on the gut microbiota, up to a point. But too much exercise can promote gut permeability and inflammation, partly due to a lack of blood flow to the gut and consequent leakiness of the intestinal lining. Thus, overtraining can lead to depression and reduced performance.

Knowing how training affects the gut and how the gut affects the brain can improve outcomes. With a proper diet including sufficient prebiotic fibre to optimise microbiota health, a poor doer can be turned into a model athlete. 

References

Mach, Núria, Alice Ruet, Allison Clark, David Bars-Cortina, Yuliaxis Ramayo-Caldas, Elisa Crisci, Samuel Pennarun, et al. “Priming for Welfare: Gut Microbiota Is Associated with Equitation Conditions and Behavior in Horse Athletes.” Scientific Reports 10, no. 1 (May 20, 2020): 8311.

Bulmer, Louise S., Jo-Anne Murray, Neil M. Burns, Anna Garber, Francoise Wemelsfelder, Neil R. McEwan, and Peter M. Hastie. “High-Starch Diets Alter Equine Faecal Microbiota and Increase Behavioural Reactivity.” Scientific Reports 9, no. 1 (December 9, 2019): 18621. https://doi.org/10.1038/s41598-019-54039-8.

Lindenberg, F., L. Krych, W. Kot, J. Fielden, H. Frøkiær, G. van Galen, D. S. Nielsen, and A. K. Hansen. “Development of the Equine Gut Microbiota.” Scientific Reports 9, no. 1 (October 8, 2019): 14427.

Lindenberg, F., L. Krych, J. Fielden, W. Kot, H. Frøkiær, G. van Galen, D. S. Nielsen, and A. K. Hansen. “Expression of Immune Regulatory Genes Correlate with the Abundance of Specific Clostridiales and Verrucomicrobia Species in the Equine Ileum and Cecum.” Scientific Reports 9, no. 1 (September 3, 2019): 12674. 

Daniels, S. P., J. Leng, J. R. Swann, and C. J. Proudman. “Bugs and Drugs: A Systems Biology Approach to Characterising the Effect of Moxidectin on the Horse’s Faecal Microbiome.” Animal Microbiome 2, no. 1 (October 14, 2020): 38.