Written By Dr. Kris Hiney 

The digestive tract of our equine companions is typically the system which most often goes awry. Colic and other digestive related upsets are the leading cause of death in the equine, but luckily can largely be avoided with careful management. If we understand the normal digestive physiology of the horse, we can avoid errors in our feeding program.

One of the most important features of a good feeding program for horses is providing an adequate amount of good quality forage for our horses. If we think about how a horses’ digestive system is designed to function, the relatively small stomach of the horse is designed to ingest small amounts of material throughout the day. This provides a constant influx of roughage to the hindgut, where it undergoes microbial fermentation. This is certainly the most healthy system and natural way of feeding horses. However, most horses managed in current stabling scenarios are meal fed, typically twice per day. While perhaps unavoidable, we try to offset this somewhat unnatural system by ensuring the horse receives enough forage for both its digestive health, and mental health as well.  Typically, horses will consume 2% of their body weight per day in dry matter. Most hays are usually around 85% dry matter (meaning they still retain 15% moisture after drying). For a thousand pound horse, that means that we should offer at least 23 to 24 lbs of hay per day. See calculations below:

1000 lbs x .02 = 20 lbs of DM

20 lbs DM/.85 = 23.5 lbs of hay as fed (or what you would actually weigh out)

Beyond just the shear amount of hay we offer, we should also think about the time the horse spends consuming that feed. If we again think about the natural feeding behavior of the horse, they eat for about 18 hours a day, continually traveling and searching for the most tender, nutritive grasses. When horses are deprived of feed, the pH of their stomach begins to drop, making them more susceptible to ulcers. In fact, a drop in pH of the stomach begins within 5-6 hours after the horse ceases eating. At 10 hours post feeding, the horse’s stomach is completely empty.

Beyond the obvious health risks this poses, the horse is unable to perform its natural foraging behavior. This encourages the development of stable vices such as cribbing, wood chewing, etc. which can be further detrimental for the horse’s health.

Therefore, our feedings should be spread out through the day to account for this.  Alternatively, we can offer more hay to our horse then the previously discussed 2% to allow them to participate in their normal desire to pick through their feed to select the most desirable parts. Realize this may increase the amount of hay wastage and economic loss. In addition, offering more hay can result in horses gaining more weight than desired if not offset by adequate exercise. If this is the case, look for hays that are lower in digestible energy (typically grass hays). However, this does not mean a decrease in quality such as the inclusion of dust, molds, weeds, etc.

In addition, the regular intake of roughage allows for a more stable population of bacteria in the gut. When the diet of the horse is radically altered, a shift in population of bacteria in the gut occurs, responding to the new environment supplied to the bacterial. This sudden shift in bacteria can result in digestive upsets, as well as development of laminitis. Therefore, any feed changes should occur gradually.  This includes the new pasture growing in the spring. Horses which are kept stalled or in dry lots should not be suddenly turned out into rapidly growing pastures in the spring. Ideally they should be introduced gradually, increasing the duration the horse has access to the pasture.

While maximizing forage intake is certainly ideal, what if you have a horse which cannot meet its energy needs through forage alone? Such horses usually fall into our moderate to heavy work category, or our lactating mares and growing babies. These horses then need to have a more calorically dense energy source, such as concentrate (or grain). When we feed a large amount of concentrate to a horse, the pH of the digestive system also changes, which may be detrimental. To avoid this, it is advisable to feed no more than .4% of the horse’s body weight in non-structural carbohydrate at any one meal. Our traditional grains such as corn and oats are abundant in nonstructural carbohydrates, which provide an excellent source of energy, but more care should be taken in feeding substantial quantities. Alternatively, we can provide feeds which are higher in rapidly digestible fibers, such as beet pulp, citrus pulp and rice bran. Many horse feeds now contain these ingredients as energy sources. In addition, rice bran is high in fat, which provides an extra boost of calories. Fat is 2.25X more calorically dense than carbohydrates, and provides a great way to increase calorie consumption with a lower risk of digestive upsets. Fat added to feeds may also dampen the increase in blood glucose seen after feeding concentrates. Finally, a horse will need less feed by weight when consuming a fat-added feed than a traditional concentrate.

One of the final considerations to maintaining a healthy digestive system of the horse is to ensure it receives adequate water every day. Horses on harvested feeds need adequate water intake to maintain the fluid environment of their digestive tract. If forage is higher in fiber and less digestible, it is imperative that the horse receives enough water to keep digesta moving normally through the tract. Most horses consume at least ten gallons of water a day. It is ideal to provide more water than the horse consumes (i.e., the bucket should not be empty before refilling).  Also be sure that, in the winter, the horse has access to water. In cold environments rapidly freezing water may lower a horse’s overall intake and make him at risk for impaction colic. Using bucket or tank heaters or a more frequent watering schedule will ensure that everything keeps moving regularly through your horse!