Carbohydrate Overload in Horses

By Garrett Metcalf, DVM

The old saying that a little bit is good for you but a lot of anything will kill you. That is very much how it is with just about anything in life but especially grain or carbohydrates and the effects on the horse’s gastrointestinal tract.  Grain diets are great sources of caloric dense feeds for horses but when consumed quickly in one setting is a recipe for disaster. Unfortunately this happens all too often but hopefully this article will help you know what to do if this happens to your horse.

Many times we all have heard the story of horse breaking into the feed room and helping themselves to whatever grain or feed is in there. Oftentimes it is difficult for owners to know how much grain was stored in the feed room or be able to tell which horse ate the most when multiple horses are involved. The boss horse on the farm will be the most likely suspect to have gotten the most grain. The type of grain or feed source can be a factor on how dangerous the carbohydrate overload will be and how serious to take the situation when it comes to treatment. For example sweet feed can be more dangerous vs.  whole oats. What makes grain so dangerous is that it is a very caloric and carbohydrate dense energy source that can be consumed in large quantities in a very short time frame.

The physical fact that a large amount of grain entering the gastrointestinal tract of a horse is not as big of deal other than a really full stomach in comparison to what the bacteria do with the carbohydrates makes the situation very serious. Certain bacteria in the large colon of a horse like carbohydrates just as much as the horse does. These bacterium like it so much that they will rapidly overgrow and produce more of each other while harming other good bacteria with over production of volatile fatty acids, lactic acid which leads to pH changes and acidosis in the large colon as they feed on the carbohydrates. The acute overgrowth with a simultaneous destruction of mostly gram negative bacteria is what makes the horse really sick. The cell wall or membrane of gram negative bacteria contains a compound called LPS (lipopolysaccharide) or endotoxin and horses are much more sensitive to its detrimental effects than other species. LPS has very toxic effects on multiple organ systems including the cardiovascular and gastrointestinal system as well the feet leading to laminitis or founder.

Whenever a horse is suspected of getting into too much grain it is important to get the horse looked at by a veterinarian as quickly as possible. If the horse is seen with a few hours of ingesting the grain there is a chance to recover some of the grain from the stomach before it reaches the colon. The other benefit of early treatment is products such as activated charcoal, Biosponge and mineral oil can be administered into the stomach. These products will help bind carbohydrates, endotoxins (LPS) and other harmful byproducts produced by the bacteria feeding on the carbohydrates. Other steps to be taken is preventing laminitis or foundering. The endotoxins that are rapidly absorbed by the colon are harmful to the feet. Endotoxins set off a firestorm of inflammation and enzymatic destruction of the lamina. To slow this reaction down in the feet icing can be used. Just like in science class if you want to speed up a reaction you add heat but if you want to slow it down you cool it. Icing the feet buys times and helps reduce the damage to the feet.  X-raying the feet early to monitor for rotation is important as well. As another preventative measure, sole support device can be used to help prevent rotation of the coffin bone.

Horses can also develop serious colitis (inflammation of the colon) and significant dehydration from grain overload. These horses require more intense care and hospitalization. Often these horses will require IV fluids, antibiotics, pain management and drugs to combat endotoxemia. Protein losses from the blood secondary to the colitis can lead to further dehydration and dependent edema requiring supplementation with synthetic colloids or plasma transfusions. 

It is often difficult to know what amount of grain a horse ingests when it breaks into the feed room and how serious the horse’s condition will get. Most veterinarians’ error on the side of caution and treat horses aggressively in these situations to avoid a poor outcome. It is important for treatment to be initiated sooner rather than later so don’t hesitate to call a veterinarian to see what the best course of action is whenever faced with a grain overloaded horse.