Written by: Shannon Pratt-Phillips, PhD.

How the horse’s diet is important in preventing gastrointestinal disturbances that can be painful and even life-threatening.

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Pam Mackenzie photo

Colic is a term used to describe digestive upset which can be caused by several conditions associated with the gastrointestinal tract. The pain associated with colic is often due to some kind impaction (blockage), twist (torsion) or displacement of the intestines. This can result in impaired blood flow to the digestive tract tissue and tissue death, which causes pain and could be life-threatening.

Horses are at risk for such issues in part because of the anatomical design of their digestive tract, with several turns, such as the pelvic flexure where there is a 180-degree turn, and changes in diameter throughout the intestinal tract. Adding to the complexity of the situation is the microbial population that lives within the horse’s large intestine in their own fragile ecosystem. A common saying among veterinarians and nutritionists is “healthy bugs, healthy horse.”

A multitude of causes

Some causes of colic have little to do with feeding or nutrition, such as impactions caused by parasites such as roundworms (ascarids), and some relatively uncommon events such as strangulating lipomas – benign fat tumours that “strangle” off a portion of intestine.

Impaction colic may be caused by parasites, but can also be a result of inadequate water intake, whereby feed material moving through the intestines is too dry and gets lodged. Some types of feed are also suspected of increasing the risk of impaction colic, even when water intake is normal, such as Bermuda grass hay. The fine stems of such hay is not always chewed properly, causing relatively large boluses of hay to be swallowed intact, which can cause blockages. (Bermuda grass hay can be perfectly fine, but when it is older and more mature, it is coarser and harder to chew).

Older horses and others with poor dentition may also be at risk for impactions, similarly due to lack of adequate mastication of feed. Thus, prevention of some types of impaction includes management strategies to ensure sufficient water intake. These include heating water in cold weather to ensure intake doesn’t decrease, ensuring dentition is adequate by regular veterinarian and dental checks, and making sure the feed quality is high.

Horses consuming pasture in sandy soil, or even consuming hay off the ground in a dry lot, are at risk of consuming significant quantities of sand. This sand may settle within the intestines, causing blockages, or may irritate the intestinal lining. Enteroliths are balls of mineral that have surrounded some kind of foreign substance (in many cases sand; similar in theory to how a pearl forms). Enteroliths can become quite large – even the size of a baseball! – and can block the intestines. Prevention of sand-related colic includes avoiding feeding the horse off the ground where possible, or if fed in sandy pastures, offer a regular psyllium supplement which has shown to be effective in helping to move sand through the digestive tract to avoid it settling.

One of the most common causes of colic is related to dietary-induced disturbances to the microbial ecosystem within the large intestine. Within the cecum and colon are millions of microbes including bacteria, fungi and protozoa which ferment the fiber found in hay and pasture grasses within the horse’s diet. The composition of, or changes to the diet, results in different fermentable substrates to the microbes, which can cause a shift in fermentative activity and byproducts, as well as a shift in the microbial populations. This may result in an increase in compounds such as hydrogen (and an associated drop in pH), methane gases and lactic acid. Gases can accumulate and cause parts of the digestive to “float” and move out of place, resulting in torsions and twists, or gases may affect motility, resulting in spasmodic colic. Lactic acid and a drop in pH can irritate the intestinal wall lining and kill off other populations of microbes that may release toxins upon their death.

Feeding and management strategies

Maximizing the amount of forage (hay, pasture) you feed your horse is one way to help decrease the risk of colic. Forage is what the horse’s digestive tract was “designed” to deal with, and we tend to see more problems in horses when forage is limited. A basic rule of thumb is to feed at least 1% of a horse’s body weight as forage, and ideally more.

Some horses, however, have a higher nutritional requirement than what can be provided for in hay alone, and therefore need concentrated nutrients such as those found in grain mixes. Feeding grain can be a risk factor to colic, as the risk of colic increases by almost five times when between 2.5-5kg is fed per day, and six times when more than 5kg of grain is fed. Grain is problematic, because it appears that the horse has an upper limit to the amount of starch – the main component of most grains – they can digest in the small intestines. This means that more starch will reach the large intestine, affecting the fermentative activity, and ultimately causing large amounts of gas and lactic acid to be produced.

If you do have a horse that needs extra nutrition above what can be provided in hay, you can either increase the number of meals fed per day (smaller meals decrease the load on the intestines) or look for feeds that have less starch (often measured as non-structural carbohydrates, or NSC). Good choices of feeds that are low in starch and high in digestible energy include fats (such as vegetable oil), rice bran* and beet pulp. Avoiding sudden changes to the diet will also help to keep the microbes stable. If a new feed needs to be introduced – even a new type of hay – it is best to introduce it slowly, ideally over a few weeks.

Feeding and management strategies to minimize the risk of colic include regular deworming schedules and dental check-ups, ensuring adequate water intake, as well as maximizing the amount of forage your horse consumes (ideally through pasture), minimizing grain (starch) intake or at least making each meal as small as possible, and making any changes to the diet slowly. Always consult your veterinarian and equine nutritionist when assessing your horse’s diet.

Health Q & A

Q: What are the signs of colic? A: The word “colic” is defined as “paroxysmal pain in the abdomen or bowels.” There are a number of causes (including feed-related, see “Feeding for Colic Prevention” above) and degrees of severity, ranging from mild to life-threatening – or even fatal. All cases of abdominal pain should be taken seriously, and learning to recognize the symptoms of colic in the early stages so that it can be carefully monitored may save your horse’s life.

The most common clinical signs of colic include:

Careful observation while keeping your veterinarian apprised of the situation can ensure that treatment can be administered quickly if the bout does not resolve on its own. Your vet will determine if either medical or surgical treatments are required following a rectal examination and/or ultrasonographic evaluation of the abdomen of the horse.

– restlessness – pawing the ground – refusal to eat or drink – lying down and getting up repeatedly – rolling frequently (especially without shaking afterward) – looking at the abdomen while lying or standing – standing in a “sawhorse” stance – spending more time lying down than usual – appearing to strain to defecate – grunting or groaning – no evidence of fresh manure in stall or paddock – displaying the “flehmen” response (curling the upper lip) – kicking or biting at the abdomen – sweating and appearing anxious – distension of the abdomen – capillary refill time of more than 1.5 seconds – pale, dry mucous membranes indicating dehydration – depression – elevated pulse and respiration – absence of abdominal sounds