What is Colic in Horses?

Apart from being a word that strikes fear into the heart of every horse owner, colic is the term used to describe any abdominal pain seen in horses. It is non-specific, meaning that it can be related to the stomach, small intestine, hindgut - or be unrelated to the gut altogether, as in the case of bladder stones (uroliths).

It’s important to work with your vet to try and identify the cause of a colic episode. If necessary, you can then make changes to your horse’s management or diet, to reduce the risk of future episodes.

Most colic cases are gut-related, and many diet-related risk factors for colic, and the recurrence of colic in horses, have been identified.>

Common diet-related risk factors for colic in horses

Gastric Ulcers

Studies have linked gastric ulcers – both squamous and glandular – with increased incidences of colic, but the results have been variable. Much of this variability seems to be because some horses essentially hide their pain well. In humans, gastric ulcers are associated with significant pain, but many horses can endure pain without obvious signs – which is thought to be a coping mechanism for survival in the wild.

All this means that some studies are confounded because some horses who present without colic symptoms are subsequently found to have rates of gastric ulcers just as high as those who did present with colic symptoms.

Anecdotally some horses do show colicky symptoms because of gastric ulcers. This is often seen when horses are removed from ulcer treatment before their lesions have properly healed and they then regularly experience colic after eating.

Large grain (high starch) meals

Horses with high energy demands are often fed large grain-based (high starch) meals, but several studies have shown that this practice significantly increases the risk of colic. Consuming 2.5kg-5kg of grain-based feed per day has been shown to increase the risk of colic by 5 to 6 times.

The problem here is that large grain-based meals essentially overload the horse's capacity to break down starch – so it winds up in the hindgut undigested (where it can cause a cascade of problems).

In the horse’s small intestine amylase (an enzyme) cuts up the long starch molecules into smaller glucose molecules which the horse easily absorbs and uses for energy. However, horses only produce a limited amount of amylase – so their capacity for digesting starch is also limited. What makes this worse is that large meals also move too quickly through the small intestine for the amylase to properly do its work. The upshot is that the horse ends up with undigested starch in the hindgut.

Once it’s in the hindgut, starch is rapidly fermented by bacteria who produce lactic acid as a by-product. This in turn reduces hindgut pH (from the normal ~ pH 7.0 to as low as pH 6.0). An acidic hindgut creates an unfavourable environment for the ‘good’ microbes (who ferment fibre), and in turn reduces conversion of fibre to energy and vitamins. It also changes the horse’s gut permeability (ie. causes leaky gut) which leads to it absorbing toxins into the bloodstream. Diarrhoea, impaction, inflammation, altered gut motility, distension with gas and hindgut displacement (twisted bowel) are all potential consequences – of which colic is often a sign.

Restricted grazing

Research has shown that pasture turnout is generally associated with a reduced risk of colic compared to stable confinement. One study found that horses who were fully stabled or who’d had their grazing time reduced, were 3 times more likely to experience colic than those at pasture full time.

Recent changes to feed (pasture, hay and concentrates)

Events such as changing the batch or type of hay, sudden reduction in grazing time, changing the quantity or frequency of feeding (particularly grain-based feeds) all significantly increased the risk of colic. Interestingly, it has generally been found that a recent change in hay or forage is more harmful than a recent change in grain-based feed. A change of hay in the previous 2 weeks has been shown to increase the risk of colic almost 10-fold. A separate study found that a recent change in hay posed twice the colic risk as a recent change in grain-based feed.

For horses grazing temperate or cool-season grass pastures (ie. in Southern Australia and New Zealand), sudden changes in pasture also increase the risk of colic eg. moving to a new paddock or a change in weather (generally autumn and spring). Fructans – which are indigestible sugars found in grasses – rapidly ferment in the hindgut (as discussed above for starch). While fructans only trickle into the hindgut (because grass is consumed over the entire day) they can still cause a gradual imbalance of the hindgut microbiome. It is less catastrophic than changes seen with starch, but diarrhea, inflammation, altered gut motility and distension with gas can result – and present as colic.

Poor forage quality

Poor quality (think stalky hay or straw) hay fed as round bales has also been found to increase the risk of colic.

In addition to nutritional quality, the hygienic quality of hay or haylage is extremely important. In one study, 30% of hays fed to horses that developed colic were of low hygienic quality.

Lower water intake

An Austrian study found that horses who consumed less water were at an increased risk of colic5. Hence, it’s important to provide horses with free access to clean, fresh water at all times, so that they drink plenty of it. Sudden changes in water sources such as changing from rainwater via tanks/troughs to dam access only, may increase the chances of colic. High sodium bore water can also lead to reduced water intake.

Ingestion of sand and dirt

Anecdotally, sand accumulation in the hindgut is a common cause of colic in horses (sand colic). Sand accumulation in the gut can present with unspecific symptoms in its early stages, such as ongoing episodes of mild colic, depression, unexplained weight loss or loose manure (or water with faeces). In horses with larger accumulations of sand, severe colic as the result of impactions or intestinal rupture can occur.

The risk of sand accumulating in the gut is increased by feeding horses directly on the ground when pasture is short (1-5cm) or there is no grass. A lack of supplementary forage (eg. hay when pasture is short) also increases the risk of horses ingesting sand and dirt as they try to graze short pastures to meet their daily forage needs. Soil type is also another variable, with horses living on sandy soils at most risk.

Tips for reducing the risk of diet-related colic in horses

1. Provide access to plenty of forage - Minimum 1.5% of body weight per day

Feeding adequate forage has so many benefits for helping to prevent colic. Firstly, it is the type and style of diet horses evolved to eat a – ie. trickle feeding of fibrous feedstuffs over long periods of the day. Forage provides food (fibre) for the ‘good’ microbes in the hindgut, which in turn benefits the horse. These benefits include producing energy, vitamins and many other by-products which regulate not only optimal gut health but overall health as well. A hindgut with a healthy population of ‘good’ microbes is also more resilient and better able to cope with feed changes, such as seasonal increases in pasture fructans.

Forage also provides indigestible fibre which maintains gut fill and holds large amounts of water. Together this keeps the gut full and helps prevent torsions of the gut.

Feeding at least 1.5% of body weight in hay per day is suggested to be effective at clearing sand from the gut to minimise the risk of sand accumulation. Interestingly, feeding horses hay at 2.5% of bodyweight per day was shown to be more effective at clearing sand than feeding psyllium husks7. In addition, providing adequate supplementary hay when grass is short (less than 5cm), means that horses don’t need to graze short pasture close to the soil and risk ingesting sand in the first place.

A continuous flow of forage – and hence saliva – buffers gastric acid in your horse’s stomach for a large proportion of the day. The forage also provides a physical barrier to stop gastric acid splashing up onto the delicate upper (squamous) part of the stomach – reducing the risk of squamous gastric ulcers developing.

2. Feed limited amounts of grain-based feed

And ensure grains are digestible ie. cooked (with the exception of oats).

To limit the amount of starch reaching the hindgut and causing disturbances, AND to minimise the risk of gastric ulcers, grain-based feed should be fed at no more than 1g starch per 1kg body weight per meal (maximum 2 meals per day). See the table below for examples on how much grain or grain-based feed you can safely feed per meal (as the only grain source) for a 500kg horse.

Any grain or grain-based feed (apart from oats) that you do feed your horse, should always be heat treated/processed (ie. extruded, steam rolled/flaked, boiled or micronized) to ensure easy digestion of starch in the small intestine.

In situations where horses have high energy demands, preferential use of highly digestible fibre (eg. sugar beet pulp) and vegetables oils is recommended to reduce the reliance on large grain-based meals.  

3. Provide regular pasture turnout

In most situations, free access to grazing is good for intestinal health and many colic-prone horses benefit from it. It mimics a natural diet and enables normal feeding behaviour, gentle exercise, and social interaction.

However, pasture that is rich in fructans can be counterproductive for some colic-prone horses and caution should be taken during high-risk periods such as spring and autumn. Strip grazing and supplementary hay feeding (of low sugar hay) during these periods can help reduce the negative impact fructans have on hindgut health.

4. Make all dietary changes slowly over 2 weeks or longer

Including changes in pasture and hay.

Disturbance and maladjustment of the hindgut microbes is the root cause behind many colic episodes related to recent dietary changes. Therefore, it is essential to make any dietary changes gradually, over at least two weeks. This allows the horse’s body to gradually adjust to the ‘new’ diet, including upregulating enzymes such as amylase (the enzyme which breaks down starch) or lipase (the enzyme which breaks down fats) to ensure large quantities of undigested starch and fat do not end up in the hindgut. Gradual dietary change also allows slow shifts to occur in the hindgut microbial populations.

And remember, gradual changes between forages is just as important. Hays and pasture can contain varying levels of fibre, protein, fructan etc and it takes time for the horse’s body and gut microbes to adjust to the differences. Similarly, moving from a pasture-based diet to a hay-based diet or vice versa also requires careful transition. Whilst this may not always be practical, where possible it is important to follow this rule to minimise the risk of colic.

5. Ensure feed and water are of good quality

This sounds like common sense but can sometimes be overlooked. If feedstuffs or water look or smell unusual or unpleasant to you, always be cautious and don’t give them to your horse.

If a sudden change in water source is required, always observe your horse closely to ensure they are drinking normally.

How might Digestive EQ may reduce the risk of colic?

Digestive EQ aims to support optimal digestion, promote healthy fore- and hindgut environments, and hence may assist in eliminating common causes of gastric upsets, particularly in the hindgut.

The yeast-derived prebiotic and postbiotic in Digestive EQ aims to support the desirable hindgut microbes, acting as a food source that nourishes them, promotes a healthy balance of microbe numbers and encourages a favourable hindgut environment. The aim is that this in turn will create an environment that is more resilient to change, such as that which can occur when undigested starch or fructans enter the hindgut and undergo fermentation.

Digestive EQ contains added enzymes to aid the digestion of starch (from grain-based feeds) in the small intestine. The aim here is to reduce the likelihood of undigested starch entering the hindgut.

Digestive EQ also contains marine-sourced calcium and magnesium oxide which both act to buffer stomach contents. For horses fed grain-based meals, this may limit the effects of bacterial fermentation of starch in the stomach – which can be a cause of squamous gastric ulcers.

Maintaining the integrity of the gut is also important. Digestive EQ provides a ready supply of amino acids (threonine, serine, proline and glutamine), which are building blocks used to repair and regenerate the gut lining and protective mucous layer. Digestive HP includes these and one more, leucine, for enhanced support.

What about using Stress Paste?

Stress Paste can be used to help minimise the risk of colic, and during recovery from colic episodes.

Illness, travel, strenuous exercise and other kinds of stress events, can all negatively impact healthy gut function and balance. Stress Paste is specifically designed to support gut health during these acutely stressful periods - and minimise the cascade of events which could otherwise result in colic.

Like Digestive EQ, Stress Paste contains a yeast-derived prebiotic and postbiotic to help promote a healthy balance of ‘good’ microbes. During times of acute stress, this may make the microbial populations more resilient to change. For horses recovering from colic, the prebiotic and postbiotic may promote the restoration of a healthy balance of ‘good’ microbes.

During times when horses aren’t eating enough forage to supply the ‘good’ microbes with all the fibre they need (like during long trips or while staying away from home for competitions), the yeast-derived prebiotic and postbiotic in Stress Paste may help bridge the gap and provide them with a food source.

Stress Paste also contains magnesium hydroxide and pectins. These nutrients work to buffer and protect the stomach from acidic contents, which have the potential to cause squamous gastric ulcers. On occasions when horses aren’t eating for prolonged periods of time, due to necessity ie. during travel or due to decreased appetite, these ingredients may help protect the stomach.

Stress Paste also supplies a readily available supply of four amino acids (threonine, glutamine, proline and serine) which are critical for gut health. These amino acids are used directly by the gut to continuously regenerate and grow new, healthy gut tissue. They are also needed to support the production of the protective mucus in the gut. In horses recovering from colic, gut integrity may have been compromised and hence these amino acids may aid in its repair.

Additional ingredients contained in Stress Paste include betaine, B-vitamins, vitamin C, and vitamin E, with the aim of keeping your horse eating well, hydrated, and protecting their working muscles.

Take-home messages about colic

Horses have evolved to thrive on a high fibre, low starch diet – mainly comprising a diversity of lower quality forages, consumed over prolonged periods of the day. The best diet for avoiding colic-inducing gut disturbances is one that closely mimics the natural diet – both behaviourally and nutritionally. In horses with higher energy demands (such as high performance horses) whilst it is not possible to exactly mimic the natural diet and environment, you can at least minimise the risk of colic by following some basic rules of thumb.

Here are the most important feeding tips again, for reducing the risk of diet-related colic:

1. Provide constant access to adequate amounts of forage
2. Limit how much grain-based feed you give your horse
3. If possible, allow constant or regular pasture turnout
4. Make any dietary changes slowly, including changes in forage
5. Provide daily gut support PLUS extra gut health support during high-stress periods

Colic can often be easily resolved, but sometimes it can be devastating. Always seek veterinary attention to try and identify possible causes. The risk of colic episodes that are related to diet can be minimised with appropriate management.

References

1. Sykes, B.W., Bowen, M., Habershon-Butcher, J.L., Green, M. and Hallowell, G.D. Management factors and clinical implications of glandular and squamous gastric disease in horses. Journal of Veterinary Internal Medicine. 2019, Volume 33, Pages 233– 240.
2. Tinker, M.K., White, N.A., Lessard, P., Thatcher, C.D., Pelzer, K.D., Davis, B. and Carmel, D.K. Prospective study of equine colic risk factors. Equine Veterinary Journal. 1997, Volume 29, Pages 454-458.
3.  Hudson, J., Cohen, N., Gibbs, P. and Thompson, J. Feeding practices associated with colic in horses. Journal of the American Veterinary Medical Association. 2001. Volume 219, Pages 1419-1425
4. Cohen, N.D., Gibbs, P.G. and Woods, A.M. Dietary and other management factors associated with colic in horses. Journal of American Veterinary Medicine Assoc. 1999, Volume 215, Issue 1, Pages 53-60.
5. Kaya, G., Sommerfeld-Stur, I. and Iben, C. Risk factors of colic in horses in Austria. Journal of Animal Physiology and Animal Nutrition. 2009, Volume 93, Issue 3, Pages 339-349.
6. Husted, L., Andersen, M.S., Borggaard, O.K., Houe, H. and Olsen, S.N. Risk factors for faecal sand excretion in Icelandic horses. Equine Veterinary Journal. 2005, Volume 37, Pages 351-355.
7. Lieb, S. and Weise, J. A group experiment on the management of sand intake and removal in equine. In proceedings, 16th equine nutrition physiology symposium, 1999. Page 257.