Colic conditions in the horse are very common, impacting likely upwards of 20% of all horses at some point in time in their lives.  Not all horses do experience colic, as noted by the percentages.  In those horses that do experience colic, some are isolated events, while some tend to recur over and over again. Those are the chronic colic cases and the ones that should raise some questions and concerns.  What creates the chronic cases of colic in the horse and is there a connection with those isolated colic events?  Is there a link between colic and overall digestive health in the horse?

Horse Digestion and Colic

Horse Digestion and Colic

A high majority of colic cases in the horse are linked back to intestinal related problems.  Colic, by definition, simply means abdominal or belly pain.  There are other organs in the abdomen that can create colic pain, but by far, most cases of colic are associated with intestinal related problems.  In most of the cases of intestinal related colic pain, the pain is created due to distension or swelling of that section of intestine.  This is due to either excess gas production or a blockage of some form, which allows for gas, fluid, or feedstuff accumulation, which then creates distension over time.

There are many different types of colic, but for simplicity reason, let’s try to break them down based on the origin.  These types would then include:

  1. Excess gas production
  2. Gas accumulation
  3. Infection (enteritis, colitis, diarrhea)
  4. Ulcer formation (foregut or hindgut)

Those factors are the underlying secondary pathologies that are present and often we have several factors at play in any given case of colic.  You can have a horse with excess gas production and flatulent colic, or you can have a horse with a large colon torsion, that also may have underlying excess gas production.  In either of those cases, as time progresses, you can then incorporate other pathologies including ulcers and infection.

The main point here is that I am not specifically mentioning a colic condition by name, such as a large colon torsion or small intestinal obstruction, but simply pointing out events or pathologies that are shared between colic conditions or types.

Digestive Health and Colic

No matter what type of colic you are referring to in your horse, whether if mild or severe, resolving spontaneously or requiring surgery, the root problem is often poor digestive health.  A horse can be at a weekend event competing and develop gas colic or another form, which is often short lived and responsive to therapy.  Those events often unfolded due to a change within the digestive tract, an alteration of the microbiome, which then created excess gas or maybe slowed digestion or transit time. This can be linked to stress associated with transportation, competition, being away from home, a change in the diet, feeding routine, or simply and inability to relax.

The most common links to colic and digestive health include:

  1. Dietary related
  2. Stress (emotional or physical)
  3. Poor dentition
  4. Medication related

These are the 4 main connectors with most cases of colic.  In some others, there may be parasite issues, but this is most common in foals or those horses with underlying medical concerns and immune impairment.

The bottom line is that in almost every case of colic, one of the above factors if not more, is contributing to digestive health ailments on some level, which then creates the colic situation.  A horse does not gain a large colon displacement due to rolling on the ground and scratching their back.  This act of rolling may assist the colon to slide out of normal position, but there has to be other factors at play to further create the situation.  In most cases, this other factor is excess gas production, which in this particular case allows the large colon to essentially lift up or float out of normal position.

All 4 of the factors mentioned above can impact gastrointestinal health and digestion in the short and long term, altering the microbiome balance, absorption of nutrients, excess gas production, loose stools, and inflammatory conditions. 

The Gut Microbiome in the Horse and Colic

The gastrointestinal microbiome in the horse consists of the hundreds of species of bacteria, fungi, and protozoa which colonize various sections of intestine.  This group of organisms not only impacts digestion of food stuff and nutrient absorption, but can impact the inflammatory status of the horse, hormone balance in the body, performance, recovery and healing, and even their mental status.

Think about this for a minute and realize the high incidence of one type of colic condition, referred to as gastric ulcers.  Think about how many horses have this problem and how many are on continuous ulcer medications to aid in their management.  Now, think deeply on those horses, especially if you own one.  Is the ulcer a primary problem or is it secondary?  Meaning, did the ulcer come first or was there something else?  In most of these cases, there is an anxiety condition which is behavioral in nature. Some horses express their emotions openly with pacing and are hard to handle.  Others may be more stoic, internalizing their emotions.  These emotions are the primary problem, and then feed back via the gut-brain axis and influence digestive health.  Given the gut-brain axis, considering that it works both ways, the emotions could be secondary to a dietary problem or gut problem.  It can be really hard to say, but either way the emotions are then tied back to gut health.

In most of those ulcer horses, this anxiety creates changes in intestinal motility patterns and alters the acidity of the overall patient.  The ulcers are not really created due to excess acid production in the stomach, but more so due to changes within the microbiome, which then impacts cellular health and inflammation, and leads to a breakdown of the stomach lining.  This weakness in the stomach lining is then more susceptible to irritation by the stomach acid.

Now, step back and think about how 99% of these equine ulcer cases are managed.  Do the current therapies with ulcer medications (PPI’s, or H-2 blockers) really address the problem?  Simply put, the answer is no. This is why most continue to suffer the effects of ulcers, needing to be treated intermittently or continuously by their owners.  Despite these therapies, the horses are often no better off physically or emotionally.

This same scenario plays out in almost every case of colic, no matter what type or form of colic that horse has been diagnosed with.  Those 4 factors above impact the digestive health and the microbiome. It is just a question of to what degree, what period of time, and how severe the damage is.  This then dictates the colic condition.

Thus, many owners with a case of gas colic often just feel relief after their horse responds to traditional therapy.  They should feel relief, but the question is are they, as the owner, paying attention and seeing the road signs that are presented to them?  Are they connecting the dots or do they simply walk away and wait for the next colic event?  The next time may be more severe than the last, if changes are not made.

The Equine Digestive Microbiome and Contributors

The microbiome is a vast organ system really, considering that balance in that organ system can either enhance or damage health on many levels.  The balance in this organ system can either make or break health, and even impact soundness.  It really is a delicate system, consisting of likely hundreds of different organism species, which can be impacted negatively or positively by diet, stress, medications, and other events.

In past equine research studies, there have been observations of the overgrowth of some bacterial species, namely Lactobacillus and some Streptococcal species.  These overgrowths were seen in cases of metabolic syndrome and laminitis in horses.  The microbiome has been further studied recently, using more up to date technology such as DNA evaluations, which allow for a broader evaluation of the microbiome present in the equine feces.

In human research, the main concern has been revolving around an imbalance between two main groups of bacteria, Bacteriodetes and Firmicutes.  This is not too far removed in horses, and in some more recent studies, there are indications that the Firmicutes group is more represented, indicating a higher level.  When this is noted, there is then an imbalance present, as compared to more ‘healthy’ horses.  This Firmicutes group of bacteria contains Lactobacillus and Streptococcal species.  So, past and more current research is in agreement.

What does this mean for the colic equine patient?  A lot actually.  Those past studies have focused on metabolic syndrome and laminitis, but when we look at most of the equine colic patients, many of them do have some similarities.  Many horses that develop colic are easier keeper types, being more overweight, and some have documented insulin resistance.  Other horses that colic are the leaner types, but on repeat fecal cultures, they too often have obvious dysbiosis or imbalance in the microbiome.  Interestingly enough, many of the leaner colicky horses have a predisposition to ulcers and anxiety, of which both have demonstrated dysbiosis in our research studies.  This is also noted in human research additionally.

When there is an imbalance in the microbiome, some bad things can happen, but this is not generally acute in nature.  Generally, the negative changes created by the shift in the microbiome take time, from months to years.  The horse that demonstrates colic today may actually have had an underlying problem for some time.  This may explain why many do respond to traditional therapies but relapses or have another bout in a few months.

The Gastrointestinal Microbiome and Negative Health in the Horse

The digestive microbiome in the horse is susceptible to alterations in balance at almost the drop of a hat.  There are many factors that contribute to health or imbalance within this system.  Everything can be fine in your horse while on the farm, but take a weekend trip to an event and all chaos can break loose due to stress and other factors.  Those perceived minor events can alter the microbiome in your horse within a matter of hours, and are likely responsible for the acute colic crisis seen in many out of town cases.

When the gastrointestinal microbiome is out of balance, your horse may experience:

  1. Digestive upset (gas production)
  2. Reduced nutrient absorption
  3. Gastric ulcer predisposition
  4. Intestinal pH changes
  5. Intestinal inflammatory changes
  6. Increased gut wall permeability (leaky gut)
  7. Loose stools or diarrhea
  8. Altered gastrointestinal motility
  9. Bacterial translocation (movement into the bloodstream)
  10. Immune alteration
  11. Systemic inflammatory response

This is a laundry list of events that can happen as the digestive microbiome is disturbed and out of balance.  Not every horse experiences all eleven events, but many experience at least one or two.  Think about the many horses that experience loose stools or diarrhea just with the thought of a trailer ride.  That is the impact of stress upon the GI tract, and inevitably the microbiome.

Considering that the vast majority of equine colic patients experience intestinal colic, and that most of them are gas related, it is not far stretch to then make connections with the microbiome.  Then you have to remember that many of these horses are repeat colic cases, which infers that the microbiome concerns continue despite therapy.  It should at least make you realize that a colic episode is not an isolated event.  It is more than likely a signal of a deeper seated problem within that horse.

Taking this all into consideration, along with financial aspects of colic care and the morbidity/mortality statistics, it should make you wonder if there is not a better means of intervention, more along the lines of prevention?

Read “Management Options in the Horse with Colic


We will discuss this in another article.


Author:  Tom Schell, D.V.M., CVCH, CHN

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