Help stop colic before it starts by implementing these management and feeding practices.
The thought of colic can strike fear into the heart of even the most seasoned horse owner. Since it’s the second highest (14.6%) cause of death in horses in the United States, according to a NAHMS survey in 2005, this fear is perhaps justified.
Colic comes in many forms, and while we typically think of issues relating to the digestive tract, it may not be digestive distress that is causing the symptoms – “colic” is a general term used to refer to pain in the abdomen. There is no doubt, though, that an understanding of equine digestive tract anatomy and physiology can help you make informed management decisions that will reduce the risk of colic symptoms that do result from digestive issues.
As nature intended
Approximately 17 million years ago, the ancestors of today’s horse came out of the forests onto the plains of North America. Over the millenia that followed, horses have perfected their ability to live while eating grasses of low nutritional value. Think about modern day wild horses, for example. Their diets are still comprised of forages, and due to both the plants’ sparse nature and low nutritional value, they must eat for most of the day, sometimes travelling considerable distances in order to meet their nutritional needs.
As a result, the horse’s digestive anatomy is designed to consume large quantities of poorer quality forage. Horses constantly secrete stomach acid and bile in anticipation of the almost constant supply of forage. The stomach is small, and the small intestine secretes relatively little amylase (the enzyme necessary for starch digestion) due to the low starch nature of the diet. The cecum and large colon (hindgut), which make up almost 60% of a horse’s digestive tract volume, is dedicated to the fermentation of forage, and a symbiotic relationship exists with a host of bacteria. In fact, without these digestive tract bacteria, horses would be unable to digest the complex carbohydrates that make up the bulk of their natural diet.
When you feed your horse forage, you are actually feeding the digestive tract bacteria that reside in his hindgut, which through a process of fermentation, break down the complex chemical bonds in the forage carbohydrates. The bacteria then utilize the released energy for their own survival. The volatile fatty acids (VFAs) released by the bacteria during this process are absorbed by the horse and converted into various sources of energy. Without the bacteria, this energy would not be available to the horse. In fact, for a horse consuming an all-forage diet, about 80% of his energy intake comes from VFAs. When evaluating the horse’s digestive anatomy, it becomes clear that these animals are designed to eat forage of relatively low nutritional value, and lots of it.
When access to forage is restricted or higher amounts of processed feeds are given, less chewing is necessary, resulting in less saliva production. Saliva contains buffers such as bicarbonate, which act as natural protection from the constantly secreted stomach acid. Stomach acid is secreted by the lower portion of the stomach, where the cells also secrete protective mucin. The cells in the upper portion do not secrete mucin and are susceptible to ulceration should they come into contact with corrosive stomach acid. It is not surprising then that the majority of gastric ulcers in horses are found in the upper portion of the stomach. However, forage forms a mat that floats on top of the stomach acid, preventing the latter from splashing into the upper sections. When forage consumption is restricted or long periods pass between meals, this mat becomes depleted and ulcer risk is increased. Gastric ulceration can sometimes lead to colic symptoms.
The dangers of too much starch
While the majority of bacteria in the equine digestive tract exist in the hindgut, some do exist in the stomach, and they ferment starch and other easily digestible carbohydrates. Similar to the hindgut bacteria, the end products of this process are VFA gases. If rapid fermentation occurs, as can be the case when large amounts of starch are fed, gas can build up, leading to colic symptoms. Another problem with feeding large amounts of starch at one time is that it is possible to overwhelm the small intestine’s ability to digest and remove it. When this occurs, starch escapes into the cecum and colon where it is rapidly fermented, producing lactate, a very acidic VFA, and gas, which can cause colic. There are other bacteria that will use the lactate, but if lactate production exceeds removal, the environment in the hindgut can become increasingly acidic. Bacteria that ferment the complex carbohydrates found in forage need a neutral environment, and when this is not maintained they may be killed off, causing loose manure and, in severe cases, colic.
Avoid sudden changes
A similar situation can occur when sudden feed changes are made, or horses are grazed on rich pastures high in fermentable sugars. The bacteria in the digestive tract are specific to the diet being fed, and must change as dietary substrates change. Sudden shifts can lead to bacterial disruption. All feed changes should be made gradually over a seven to ten-day period; this will help reduce the risk of colic and other digestive disturbances.
Finding a balance
It should be clear by now that management practices can increase a horse’s risk of developing colic, and that frequent exercise, access to pasture, unrestricted access to forage and reduction of starch in the diet will all help reduce colic risk. The question then becomes: how do we offer unrestricted forage if it causes some horses to gain too much condition. Conversely, how do we maintain condition on the hard keeper if we can’t feed large amounts of high starch grains?
Feeding the easy keeper
For the easy keeper, the trick is to find low calorie forages so that a greater amount can be fed before the horse’s calories needs are met. Avoiding higher calorie alfalfa and grain hays, and feeding a grass hay that was harvested in a more mature state so the proportion of leaves to stems is lower, will allow you to feed larger amounts. When the amount of hay fed needs to be restricted, using one of the many slow feeders currently on the market is a great choice, as it will slow consumption and make what hay is fed last longer. Obviously, hay should not be so mature as to be a risk for impaction colic. In general, impaction risk increases if a horse is dehydrated, so ensuring that he is consuming enough water is vital.
The hard keeper
For the hard keeper, or the horse in work that cannot maintain weight on unlimited access to forage, high starch grains can be fed – but depending on the discipline the horse is used for, lower starch options may be a better choice. Any supplemental feed should be given in small meals at no more than four to five pounds at a time for an 1100-pound horse. This is especially true for higher starch feeds – the more small meals, the better. This will help ensure that the small intestine does not get overwhelmed.
A safer option than high starch grains is a high fat feed, or a feed that utilizes so-called “super fibers” such as beet pulp and soybean hulls. These super fibers require microbial fermentation in the hindgut like traditional forages, but yield levels of energy that are more similar to oats. A caution, though – more fat is not always better, because while horses do utilize it very well, it can disrupt microbial fermentation when fed in large amounts.
Given that many of us live in urban areas and wish to enjoy our horses for riding and other disciplines, it is not possible to keep them on the open plains from which they evolved. However, by having an understanding of digestive tract function, and keeping their heritage in mind, it is possible to make management decisions that honor the equine digestive system and thus reduce the risk of scenarios that might lead to colic.
The level of sodium in the blood is one part of the thirst mechanism, so ensuring adequate salt intake is a critical management technique to reducing dehydration and impaction risk. Horses should always have access to plain salt, and additionally, one tablespoon per 500-pound body weight can be added to the ration per day to ensure maintenance sodium levels are being consumed. Fresh grass has very high water content, where hays may only be 10% water. Therefore, another way of increasing water intake and reducing impaction risk is to soak hay before feeding. This has the added benefit of reducing dust and soluble sugar.