Equine Grass Sickness

Over time, the minimum amount of forage recommended for maintaining gut health in horses has increased, largely in recognition of the increased prevalence of gastric disease. Fibre provided by forages has other important functions, not least that it is utilised by the microbiota or ‘bugs’ that live in the horse’s digestive system.

These bugs are an important part of the horse’s immune system. Signs of dysbiosis – a disruption of the population of bugs in the gut – are often very visible. Loose droppings, poor condition and colic are some of the most common problems that we can see in horses, but what we tend to overlook is that changes to the microbiota might have been occurring for weeks, months or even years prior to those problems becoming apparent on the outside. At some point, a perfect storm of events occurs, or a tipping point is reached, where the horse changes from looking in good health to having a problem.

The beneficial microbes in the digestive tract help to keep potentially harmful ones at bay by out-competing them for resources – a phenomenon known as competitive exclusion. If we keep the good bugs well fed and in an environment that they prefer (i.e. not too acidic), they should thrive. If we don’t give them enough to eat however, they will start to look for food elsewhere and that includes the mucus that lines and protects the horse’s gut. If the mucus layer is eroded, the gut cells are exposed to things they shouldn’t be which compromises their tightly organized structure – a phenomenon known as leaky gut syndrome. Whilst harmful bacteria are always a threat to an animal’s health, if the mucus layer is eroded, bacteria that are normally present in the gut performing important functions, may become problematic too. This is an important point as it might not be inherently harmful microbes that are the cause of disease.

Different horses can have different preferences so it can take some trial and error to determine the best choice of feed for your horse. Here are some things to try that may help encourage your horse to eat:

• Hand feed from a raised bucket to start with.
• Use a shallow bucket on a raised platform
• Try grated succulents such as apples and carrots – you can also put them through a blender and mix in to a mash if it will tempt them
• Add flavours like mint, garlic or diluted apple juice or fruit cordial. Appetites may vary day to day so having a variety of flavours on hand can help to stimulate interest and provide some different tastes without having to repeatedly change the base feed.
• Other herbs or flavours that your horse might find tasty include cinnamon, honey, banana, thyme, oregano, ginger, rosemary or fenugreek.
• Split the ration up into several smaller meals across the day (ideally 4-5 meals) to avoid over-facing them, starting off with small handfuls in each.
• Try different consistencies; some horses may prefer a drier feed over time whereas others may prefer a mash or wet feed.
• Try mixing it with warm water as this can enhance the aromas from the feed.
• Picking some fresh grass or hand grazing can help to increase forage intake.
• Feeding alongside or in sight of a friendly equine companion may also encourage eating.

If the horse’s appetite starts to increase, then the aim is to increase the energy (calorie) and protein levels in the feed to try and restore the weight and condition that has inevitably been lost as a result of EGS. Given the extreme disruption to the gut, providing some digestive support is recommended. There are no live bacterial probiotic supplements approved for use in horses and so the following categories of digestive aid are recommended:

• Probiotics – live yeast is approved for use in horses. Yeast are fungi and fungi are an important part of the fibre digestion process so supplementing with yeast helps horses to get more out of their forage.

• Prebiotics are ingredients that feed beneficial bacteria in the gut. FOS prebiotics provide a food source for bacteria helping them to flourish and thereby keeping pathogenic species at bay.
• Postbiotics are non-living microorganisms or fermentation products that provide health benefits. They can help support the gut’s natural defences, particularly during times of stress or digestive upset.

A combination of these digestive aids is recommended in an extreme case such as EGS. They are all approved ingredients which means they have demonstrated a good level of safety and efficacy.

A longer term feeding strategy for an EGS case will largely be influenced by how much the horse will eat each day especially in relation to forage. For those whose appetite is still very limited, liquid oil or high oil feeds are very energy dense and so can provide a lot of calories in a small volume of feed. However, they tend to be less palatable than feeds higher in carbohydrates, so may not be well-received.

Feeds that already contain a high level of oil as part of the formulation commonly have added flavours to help aid palatability as well. These may come in the form of high oil pelleted supplements or chopped and pelleted fibre feeds containing added oil. Micronised linseed is another option which can be tastier than liquid oil, and up 100g per 100kg of bodyweight daily is an appropriate quantity to aim for if the horse will tolerate it (i.e., 500g per day for a 500kg horse).

Balancers provide some quality protein and vitamin and minerals in a small volume of feed and so although they aren’t high in calories, they are a useful way of trying to supply a lot of nutrients. Broad spectrum vitamin and mineral supplements are easy to mix into a mash but are unlikely to supply as much quality protein. This may not be an issue depending on what else is being consumed. We really recommend speaking to a nutritionist to help ensure the diet is balanced for the longer term.

A phenomenon called refeeding syndrome exists whereby if too much is fed too soon, a rapid rise in blood glucose and an associated surge in insulin ensues. The insulin drives glucose and potassium into cells which also utilises other minerals and electrolytes. These are depleted because of the horse’s illness, and so the sudden shift away from other functions can cause organs to fail – most commonly the kidney, lungs, and the heart. The most common time for this to occur is three to seven days after refeeding starts and it can be a major problem. Though the temptation may be to feed a higher volume as soon as your horse seems like they want to eat it again, it is important to reintroduce feeds slowly and to use feeds that are less likely to result in refeeding syndrome.

Independent research from the US has shown that one way to reduce the risk of refeeding syndrome is to use high fibre feeds like alfalfa as it is low in starch and so doesn’t cause the increase in glucose and insulin associated with feeding cereals. It is also relatively abundant in minerals such as potassium, magnesium and calcium and provides good levels of quality protein to support the horse’s recovery. Alfalfa pellets may work well here as they can be soaked for ease of chewing. Although not included in the study, the same can be said of unmolassed sugar beet pulp which is also low in starch and sugar and contains a valuable level of calcium.

There is currently no diet or feeding programme that has been identified to prevent EGS. However, given the recognised associations between EGS and factors such as grazing, conserved forage, dietary change and stress, there are sensible steps that owners can take to support digestive health and potentially reduce exposure to some of the associated risk factors.

Feed plenty of fibre
For long term health and well-being, a horse should consume a minimum of 1.5% of their current bodyweight in forage on a dry matter basis per day. For a 500kg horse, this equates to 7.5kg in dry matter per day.

However, different forages contain varying amounts of moisture which dilutes the fibre and nutrients supplied, so the amount required when weighing out their haynet will need to be slightly higher. For example, 7.5kg in dry matter equates to approximately:

• 8kg of hay as fed if it is 85% dry matter (15% water)
• 5kg of haylage as fed if it is 65% dry matter (35% water)

These figures represent a minimum daily intake and can be adjusted according to grazing availability and the individual’s needs. Horses who are underweight or struggling to maintain condition will likely require more forage. Even if forage is fed to appetite, it is good practice to weigh how much is provided and how much is left over to monitor intake and ensure your horse or pony is consuming enough. It can be helpful to speak to an equine nutritionist for individual advice on forage quantities.

If your horse or pony gains too much weight at this level of intake, then it is better to use a lower nutritional value forage rather than reducing the amount fed. Straw can be a great option for making a difference to calorie intake – replacing one third of the weight of an average hay with straw reduces a horse’s calorie intake by around 16%. Replacing a better-quality forage such as haylage with straw can make an even bigger difference. Recent studies have shown that up to 50% of the forage ration can safely be fed as straw with no increased risk of gastric ulcers. Do check with your vet before introducing straw if your horse or pony has a history of impaction colic or doesn’t have the best teeth!

Use conserved forage at high-risk times
If you can’t provide access to conserved forage all year round then ensure it is supplied at high-risk times such as when introducing new horses to the herd, moving fields, or during greater differences in temperature or weather conditions. This includes during drought conditions or over the winter when grazing is reduced.

Ensure the diet is balanced
Good doers are often underfed vitamins and minerals as they are kept on restricted rations. These essential nutrients are an important part of the horse’s immune system. Low calorie ways exist to supply a balanced diet in the form of broad-spectrum vitamin and mineral supplements or balancers. It is important to ensure these are fed at the manufacturer’s recommended amount for the horse’s size and level of exercise.

Make dietary changes slowly
Sudden changes to the diet (including a change in forage) can impact on the gut microbiota, so it is important to make any changes gradually over a couple of weeks. The bacteria in the horse’s digestive system thrive in a consistent environment. Sudden changes to the diet can cause bacteria to die off as their environment becomes less hospitable. This can result in the production of toxins which may result in problems such as colic or other digestive disturbance. It is important therefore that any changes to the forage are made gradually wherever possible as well, such as changing onto a new batch of hay or haylage or moving to a different field.

Try to keep stress to a minimum
Since stress is a recognised risk factor for EGS, it is sensible to objectively review practices on the yard and identify any that may be causing stress. This could include social isolation, unsettling herd dynamics with companions or field mates, or having multiple different handlers or riders. Pain or discomfort from other causes can also be a source of stress so take steps to rule out any other potential issues. Adding a digestive aid to the ration at times of unavoidable stress like a change of yards, a loss of companion or when travelling or staying away may help to minimise the disruption to the microbiome.

Given the unique circumstances of Equine Grass Sickness, we recommend contacting a nutritionist for advice and guidance for each horse as the appropriate amounts of each feed will vary considerably. The Equine Grass Sickness Fund is a good source of further information and advice.