University of Vermont AAHS

Faulty Fueling Systems: Equine Version

Elizabeth Greene, Ph.D.
Extension Equine Specialist
University of Vermont
Member, AAHS Board of Directors

[reproduced from Caution:Horses, Vol. 4, No. 4, Winter 1999]

What if horses were cars, and "equi-mobile" producers were held accountable for the safe and proper function of their products? If this were the case, there could be potential class action suits against major equi-mobile producers, such as "Pegasus" and "Spottybody" for gazillions of dollars. Why? The plaintiffs would be able to prove beyond the shadow of doubt that numerous design faults exist in these prototype vehicles. Once the media got the word out to the consumers, all equi-mobiles would be recalled.

Imagine the following courtroom argument:

Plaintiff's Lawyer: My client bought her 1999 Pegasus without the knowledge of flaws in the design of the fueling system. As a result, she has incurred multiple vet-mechanic bills, has experienced severe anxiety, pain and suffering. And, the engine of her Pegasus completely locked up and cannot be repaired. My client's equi-mobile is a total loss.

Defense Lawyer: Although some design "challenges" with the Pegasus have been identified, it is clear that the plaintiff was not following equi-mobile maintenance protocol. In fact, we have witnesses that will testify that she used improper fueling methods, did not provide adequate water for the cooling system, and did not provide recommended work hours for the fuel mix that was utilized.

Does this sound far-fetched? Unfortunately, this scenario is an appropriate metaphor for the gastrointestinal tract of the horse. In order to become familiar with the design flaws of our equi-mobiles, we should examine "life before humans" in the horse's evolution and compare it with the "typical horse" of today. Then, with the proper understanding and maintenance of the system, we may be able to prevent many "engine lock ups" on our horses.

Many of the "design flaws" were once a natural and functional part of the horse's daily existence. The horse was designed as a free roaming animal that constantly grazed on low to medium quality forage. As a result, he developed a very small stomach in relation to his size and intake. This was not a problem, since his main exercise involved fighting, playing, breeding or the occasional sprint from a predator. In addition, the horse has a one-way valve (cardiac sphincter) at the entrance to the stomach. This prevents the horse from vomiting if he ingests something inappropriate. Horses are not likely to consume poisonous plants unless there is nothing else to forage. Since there were no fences, they were free to move to a new grassy spot in search of forage. Also, in those days, if the horse did eat something bad, the "survival of the fittest" form of selection came into play. The dumb, slow, sick and injured horses simply did not make it. Other significant design flaws in the GI tract include several sites throughout the intestines where the digesta path quickly changes from a four-lane highway to a single lane tunnel with several hairpin-curves along the way. Therefore, there is a high predisposition for physical blockage or impaction at these sites.

The cecum, located at the beginning of the large colon, is a large pouch where fiber digestion occurs through bacterial fermentation. Here is another potential area for incomplete passage of digesta and for other problems with the microflora that live within the cecum. If the horse has a sudden change in diet, it can cause a major change in environment in the cecum. This can cause the death of bacterial microflora and subsequent release of endotoxins into the cecum. If the endotoxins are absorbed into the blood system, colic and/or laminitis can result. When microbe changes occur, there is often an increased gas accumulation and lactic acid production due to bacterial endotoxins.

An additional characteristic is that a large portion of the horse's GI tract is "free floating." In addition to a high potential for a twist or torsion, there are a few "booby traps" including the renosplenic ligament, where a portion of the gut can become lodged or tangled. Also, the internal diameter (lumen) is not always large enough to accommodate foreign objects passage. If something becomes lodged between folds (saculations), it may immediately cause a blockage or instead continue to collect material through crystallization and eventually form an enterolith. Finally, the small intestine is dependent on one source (cranial mesenteric artery) for blood supply. If this artery is damaged or flow is compromised due to the migration of strongylus vulgarus, for example, it has the potential to affect a large area of the GI tract.

There are factors that we may not usually think about that may have a strong impact on horses' digestive abilities. For example, exercise or extreme cold may cause a pulling or diverting of the blood from the gut to either the skeletal muscle or the extremities, brain and heart. Also, if a horse is "stressed out" or is very excitable, this alone may lead to a colic bout. The gut motility is controlled by the autonomic nervous system, which is affected by "state of mind." When the horse has a fight/flight response, the body will channel blood away from the gut and toward muscles/head/heart to "allow escape" to occur. So, a "Maalox moment" in your horse's day may affect gut motility, leading to colic. To understand how fast changes can occur due to stress, think back to an equine friend that didn't want to go in the trailer and remember just how little time it took for his manure to take on a more liquid form.

Let's examine a horse of today's world in an intense training program for a competitive event. This horse is asked to work or train significantly harder than he ever would on his own. He carries an additional 10-20% added weight (the rider) and works longer. His diet is completely at the mercy of the human and is usually comprised of high quality forage and a concentrated ration that has significant amounts of energy and protein. The diet may be broken into two feedings per day with ad libitum water. The roaming and grazing capabilities have ended with the construction of high quality fencing and/or continuous stalling. So, rather than grazing throughout the day, the horse is presented with two high-energy concentrated meals. Sometimes, the grain ration remains the same even when the horse is given a few days off from training. This, too, may lead to other metabolic problems. The typical racehorse may spend 22-23 hours per day in a 12x12 stall. Also, crowded or overpopulated areas may make it more conducive to his having an increased parasite load in his system. Parasite infestation and/or damage can predispose horses to colic.

The knowledge of a horse in its natural habitat should make it clear that human management or mismanagement does play a big role in the health of the horse's gastrointestinal tract. Ready to sell that equi-mobile yet?

Horses can have extremely variable pain thresholds. A few gassy bubbles may cause one animal to drip sweat and try to roll, while his pasture mate in the same situation may look at his flank and go back to grazing. This makes it very difficult for a veterinarian to give a confident opinion on the type and potential outcome of a colic bout. It can be very beneficial for the outcome if the owner is observant and aware of the horse's normal behavior. You can peruse the following examples of some situations that I have been exposed to and see just how much variation can be found between colic cases.


The Stoic Old Man-Chance, 16 yr old Appaloosa: Chance was very docile. His normal behavior involved very little unnecessary movement, and it was fairly normal to see him lying down out in the pasture or field. One of the Horse Cooperative students noticed that he was lying down when she came up to ride in the morning, and that he had not moved when she stopped by later. His signs were much less severe than many colic cases, but the vet could palpate a small blockage in his large colon. He was treated around 8:00 p.m. at the barn with banamine to decrease pain and was "tubed" with oil to help pass the impaction. He got more banamine on a recommended schedule during the night when his respiratory rate rose and he began to show discomfort. At 7:00 a.m. we brought him to the vet school, and they continued treatment. He was put on intravenous fluids to help combat dehydration. People were fairly optimistic that he would pass the blockage on his own based on behavior and rectal palpation, but he did not. He began to bloat, and the toxins were being reabsorbed into his system, poisoning him from the inside out. As we were trying to justify a minimum of $2500 for colic surgery on a horse that was not economically worth more than $1000, Chance made the decision for us and died on his own.


The Wimpy Guy-Seneca, 7 yr old Morgan gelding: Seneca is bred for the show ring and is somewhat high strung and energetic. He was very uncomfortable in the paddock. He was breaking out in a sweat, trying to roll a little, obviously in distress. He pawed, looked at his flank, had an increased respiratory rate, and had a pained expression. He was walked for a while, given banamine and did not improve. It appeared to be a very serious situation. We took him to the vet school that evening, where they "oiled" him and watched him around the clock. He was basically recovered the next morning with little or no further intervention. Was he a wimp? Did the trailer ride get the "bubble" moved on down the tract? Who knows? He is fine and functioning today.


Rosebud, 6 yr old Thoroughbred Mare and her foal, Blossom: Rosebud, our "borrowed broodmare" was not drinking and was showing mild signs of discomfort around 16-24 hours post-foaling. She had passed minimal feces and was showing signs of dehydration when we performed the skin elasticity test. She and "Blossom" took a late night trip to the vet school, where they performed an examination, took a blood sample to look for any abnormality in her blood work, and did a "belly tap" to check for signs of a perforated bowel or infection. A rectal palpation did not seem to show any problems. She was put on intravenous fluids and watched. She took 2-3 days without feed, and only I.V. fluids and water, gradually returning to normal. There was no dramatic change, just a gradual recovery until she finally passed manure and regained hydration.


Artemis, aged Tennessee Walking Horse: Artemis was a show mare that had experienced a serious bout of colic the prior summer. During the second bout, she was treated on the farm with oil and painkillers to lessen her discomfort. She was walked for most of the night, because she refused to stand still, and would try to roll. When conservative methods of treatment had failed, the local vet indicated that surgery would be our only option for saving her. When she was opened up, the veterinarians found and removed two five-gallon buckets worth of necrotic (dead) intestine. She survived the surgery, but when she was taken off fluids, she eventually died. Her problem was most likely related to a previous severe worm infestation. The digesta had been passing through the dead gut, until finally, one day it had become twisted or blocked.


Weanling Thoroughbred Colt at Horse Sales: The horse sales can be an exciting and exhausting time for the young animals. Not only do they have a complete change of scenery, but they usually go from playtime at the farm to 24-hour stalling with continuous "hounding" by grooms, vets, handlers, and potential buyers. This particular colt had been shown a great deal and had submitted to numerous sets of radiographs (strong, clean joints), testicular palpation (future breeding potential) and endoscoping (clean respiratory tract for racing) by the veterinarians for potential buyers. When he went through the auction ring he was sold for $350,000. Upon returning to his stall, the colt began to show mild signs of colic. He was given a painkiller and walked. He seemed to be getting better until the medication wore off. He appeared to have a gas build up that would calm with painkillers. That evening, he had not improved, and was taken to the vet clinic in a fast (and hair-raising) van ride down the windy back roads of Kentucky. When the veterinarians opened him up, they found that he had a portion of his bowel "hung up" on the renosplenic ligament. The gas would build up at the hang up spot. Then drugs would allow some relaxation, some passage of gas, and thus temporary relief. He would not have recovered on his own, but as a result of the surgery, he recovered completely.


Mature Palomino pleasure mare: You couldn't kill this mare with a nuclear explosion. She was a boarder at Legacy Farm. During daily stall cleaning, we would come upon the latest things that she chose to ingest, including the parts of a light bulb (from which she had torn the protective wire caging prior to eating it) and a glove that was completely full of manure in various stages of digestion. How these things did not get held up in or damage her gastrointestinal tract is beyond the imagination.


Take home Message: Know what is normal for your horse and provide him with an appropriate diet and environment based on his needs. Do not make sudden changes in the diet, and provide plenty of fresh, clean water and good forage to keep his fueling system running smoothly. 

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