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10th September 2006


Colic is one of the most dangerous and costly equine veterinary problems in Australia. It is estimated to occur in one out of every ten mares each year.

The following article from the WA Breeders Association magazine Sunspeed Racing is a discussion paper on several management aspects which will help you to understand and hopefully reduce the incidence of colic.

Risk Factors for Colic

  •  Change in diet
  •  Change in feed type and intake
  •  Poor quality indigestible hay
  •  Grain intake greater than 2.5
  •  Eating sand
  •  Spoiled feed
  •  Restricted water access or intake
  •  Electrolyte abnormalities
  •  Change in activity/management
  •  Teeth problems
  •  Transport
  •  More time in stable
  •  Parasites
  •  Administration of wormer
  •  Previous history of colic
  •  Breed – arabs
  •  Age – new born foals and older horses
  •  Cribbing
  • Medications inc NSAID

Signs of Colic

The signs of colic are quite variable – remember colic is the term given to any horse showing abdominal pain. Signs depend upon the cause of the colic and are listed in the table below along with the frequency at which particular signs are shown by horses with colic.

Signs shown by horses with Colic

  •  Rolling 44%
  •  Pawing 43%
  •  Lying down 29%
  •  Getting up and down 21%
  •  Flank watching 14%
  •  Lip curling 13%
  •  Backing into corner 10%
  •  Kicking at belly 7%

Internal Parasite Control

Parasitic load has long been considered as a potential cause of colic. There are several mechanisms by which internal parasites could cause colic symptoms in horses.

Two of the most obvious mechanisms include damage to the blood supply and decreased motility of the digestive system. Research has reported the benefits of routine administration of oral anthelmintics to reduce the incidence of colic. Therefore, it is recommended that horses be maintained on a regular internal parasite control program tailored to their individual parasite load.

Quantity of Fibre

Anatomically, horses have developed a specialized digestive system, which allows them not only to survive, but also to thrive on high fibre diets. The caecum and colon collectively hold approximately 80 to 100 litres of liquid, and house billions of bacteria and protozoa, which produce enzymes that ferment plant fibre. The horse’s small, one-compartment stomach stresses the need for a continual intake of feedstuffs. Taken together, a small stomach coupled with the large capacity of the fibre fermenting hindgut, make the horse ideally suited to graze.

Horses on pasture graze for up to 17 hours a day and nearly continuously with distinct breaks in grazing activity occurring only between 3.30am and 4.30am. Researchers have established a link between access to pasture and the incidence of colic in horses. They reported that there was a significant decrease in the odds of a horse with colic if the animal had access to pasture. These studies point to the need for horses to graze continuously and a decreased likelihood of a colic problem if horses are allowed to graze. It is the experience of these authors and our field experience that lush, high-moisture spring pasture can also be a colic risk in horses. Colic problems in horses consuming large amounts of high-moisture, low-fibre grass virtually disappeared when horses were offered dry hay while grazing these pastures. Therefore it is recommended that horses have access to pasture whenever possible, and be provided with additional dry hay when pastures contain a high-moisture and a low-fibre content (lush spring pasture).

Horses confined to stables have an increased likelihood of colic. Many mechanisms could account for this increased risk. First, stabled horses have the desire to consume forage in a continuous manner; however, they are routinely fed their forage in two distinct meals (morning and evening).

Secondly, stabled horses may not be receiving adequate forage to maintain proper gastrointestinal function. This may be the case with horses being fed restricted amounts of hay and chaff hay to maintain or reduce bodyweight. Lucerne hay typically contains more calories per kg than grass hay or oaten/wheaten chaff. Therefore, horses fed lucerne are often fed fewer kg of hay per day than horses consuming grass or oaten hay. Not only are horses fed lucerne receiving fewer kg per day, reducing the amount of time spent eating, but lucerne hay also contains less fermentable fibre than grass or oaten hay.

Since horses seem to have an absolute requirement for forage in the diet to prevent colic, it is recommended that a minimum of one kg of dry forage (hay/pasture) per 100 kg of body weight per day be provided. For horses confined to stables, the selection of lower calorie hays or chaff (grass type) will provide the horse with more forage and mimic the continuous feeding behaviour during grazing.

When horses are fed chaff rather than hay there is often a reduction in the quantity of fibre fed, as chaff is very light and fluffy compared to hay. A 20 litre bucket of chaff only weights a little more than a biscuit of hay. This means it is common to feed less chaff than you would if you fed hay, and this is especially important in horses that are stabled full time. Another consideration is that chaff is mainly short fibre compared to the long fibre in hay. In cattle there is a requirement for some long stem fibre in the diet and our experience is that there is a higher risk of colic in horses fed all their fibre as short cut chaff. For that reason do not be concerned if you are feeding rougher cut chaff which has longer fibre length and in fact it is probably a digestive benefit for your horse. For one thing, chewing time and saliva production will be increased with larger fibre particle length.

Quality of Fibre

The quality of fibre fed can also influence colic potential. Mycotoxins, which are toxic compounds produced by moulds, have been linked to colic in horses. Do not feed mouldy feeds to horses and store feed to reduce the risk of it going mouldy. Other toxic substances occasionally ingested with forage can also cause colic symptoms. Another indicator of fibre quality is fibre digestibility. Wheat or oat straw, a relatively indigestible fibre source, has been implicated as causing impaction colic in horses. The high lignin and silica content help the plant hold the grain up and the silica gives it the shiny appearance. Rice straw and rice hulls are even less digestible as they have an even higher lignin and silica content. Impaction may result from a lack of fermentation of the indigestible material in the hindgut. Horses cannot digest or utilise these poor quality forages as effectively as cattle. Data on the precise amount of poorly digested fibre that can safely be included in the diets of horses are not available. However, the poor physical appearance and performance of horses fed this type of diet should set practical limitations. Be careful feeding tropical forages as these hays can also be very indigestible.

Enhanced fibre digestibility has been reported with the addition yeast culture to the diet of mature horses. The addition of live yeast culture may provide a mechanism whereby horses can more efficiently utilize forage of marginal quality and we include yeast culture in several Equivit supplements and Pegasus feeds formulated by Kentucky Equine Research. Yeast Culture may stimulate activity of beneficial microbes in the large intestine, particularly bacteria that digest cellulose. This can lead to an increase in the fermentation of cellulose and other fibre fractions. There are anecdotal reports of a reduction in the incidence of colic when yeast culture is added to the diet.

Grain Feeding

Since horses are anatomically designed to digest fibre, the addition of grain concentrates to the diet is a potential risk factor for colic. US researchers reported that daily feeding of grain concentrate from 2.5 to 5kg per day and above 5kg per day increased the risk of colic 4.8 and 6.3 times, respectively, compared to horses fed no grain. The exact mechanism for this increased risk for colic was not determined; however, several studies on the site of grain digestibility offer at least a partial explanation.

Normally, grain concentrates contain large amounts of starch that are enzymatically digested with their end products (simple sugars) absorbed in the small intestine. Several factors are known to influence the rate and extend of grain digestion in the small intestine. One factor is the source of starch. Various sources of starch (i.e. oats and corn) differ in the architecture of their starch granule, which has a large impact on how well they are digested in the horse’s small intestine. The precaecal (small intestine) digestibility of these two starch sources averaged 84% and 29% for oats and corn, respectively. Starch, which is not digested in the small intestine spills into the large intestine where it is fermented by bacteria. Unfortunately, one of the end products of microbial starch fermentation is gas and another lactic acid, which irritates the gut lining and decreases intestinal pH. The increase in acidity causes other bacteria to die and release potentially fatal endotoxins. All of these situations can potentially cause the horse to colic.

Processing the starch in grain (crimping, rolling, grinding etc.) can also influence small intestine digestibility. Finally the amount of starch fed in a single meal and its rate of intake will influence precaecal digestibility and safety of the feed and the water content of hindgut. Large meals of grain don’t stimulate drinking like a meal of hay does and can reduce the water content of the large intestine, increasing the risk of impaction colic.

This knowledge regarding starch digestibility would lend several recommendations to grain feeding in horses to decrease the risk of colic. First, processing of the grain will increase digestibility in the small intestine and decrease dangerous changes in hindgut gas and acidity. Steam flaking/rolling, pelleting, micronisation and extrusion are efficient methods for processing grains intended for horses. Second, limit the amount of grain provided to no more than 2.5kg in a single meal. When high intakes of grain are required by the horse, a number of small meals are preferable to one or two large meals. The use of dietary fat or digestible fibre eg lupins as an energy source is also a valid method to reduce the amount of grain needed in the diet. Don’t forget that forage in the form of hay and chaff can contribute a lot of the energy and protein needed by the horse for the horse that is spelling or in light/intermittent work.

Sand Colic

Sand colic is a particular problem in horses kept in sandy areas, even if they are not grazing. Horses often eat dirt or eat their feed on the ground this taking in sand in the process. Some of the sand then accumulates in the lower parts of the large intestine and can lead to a blockage or impaction. If you suspect your horse to have a sand buildup you can add water to the manure, mix it up and then see if the sand settles to the bottom of the mix. If you are in a risky area, try to prevent your horse eating sand by making sure all feed is fed in bins or racks off the ground and the horse can’t tip the feed bin over. Feeding enough hay will also help keep the sand moving through the gut and reduce the accumulation. Pysllium husks are also used for the same purpose, but some horses require regular paraffin oil drenches to move the sand on.

Water Intake
Water is the most vital nutrient of all and dehydration from sweat loss or reduced water intake will lead to an increased risk of colic. This is sometimes associated with electrolyte abnormalities that lead to changes in gut motility but more commonly, it causes the contents of the hind gut to dry out and can lead to “tight balled” droppings or to impaction colic. If water is too hot or cold, or tastes differently, it can lead to a reduced intake and an increased likelihood of colic. It should be pretty simple to supply a horse with free choice palatable water but it doesn’t always happen.

Action if your horse has Colic

Colic is a veterinary emergency as horses are often in serious pain, early treatment gives better outcomes and the horse can hurt itself when reacting to the pain of the colic. So you need to call your veterinarian, take away feed and water and prevent the horse from hurting itself. Walking a horse with colic may prevent it rolling, but many horses prefer to lie quietly rather than being marched around on the end of a lead rope.

Insured Horses

It is most important that you immediately advise your insurer once Colic has been diagnosed.

With thanks to Sunspeed Racing – www.watba.com.au