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The Metabolic Horse; Digging Deeper into Insulin Diagnosis Part Two

The metabolic and insulin resistant horse.  Quite a complex situation and one that is often poorly managed, as most chronic health ailments are in the horse and other species.  In part one of this article, I discussed the underlying biochemical problems in the average horse with metabolic syndrome and insulin resistance.  It may appear to be a very complex problem, and it is to some extent, but if you can see the problem and not ignore it, then options become readily available for improved management in the horse.

The Metabolic Horse and Insulin
The Metabolic Horse and Insulin

Metabolic syndrome and insulin resistance in the horse is a chronic disease, a direct effect of ongoing inflammatory and oxidative stress damage in the body.  As discussed in part one of this article, oxidative stress is a fact of life, and the reason our horse’s age.  However, in many cases, certain factors ignite that pilot light of oxidative stress, fueling the fire, and speed up damage in the body.

Defining Insulin Resistance and Metabolic Syndrome in the Horse

In part one of this article, I defined metabolic syndrome and insulin resistance in the horse, but let’s take a closer look.  In the horse, if blood work is done, normal insulin levels are reported in the range of 10-40 uIU/ml.  That is a pretty wide margin of normal values.  Take into further consideration that these normal values were once established by selecting a large group of horses, testing them, and establishing the mean values or average values, which then gives us the ‘normal’ values used by laboratories. Despite this, keep in mind that there are other factors at play.  First, we may have ‘normal’ horses that are either above or below this normal range as reported.  Second, when establishing those normal values, how do we know the horses in the higher end range were really healthy??

In my research, what I have found is that the horse often mirrors human values in many regards. Blood sugar levels in the horse are often reported at normal with a range of 75-115 mg/dl.  This is not too far off from human standards.  In the not so distant past, human medicine regarded a fasting blood sugar level of 100 mg/dl to be ideal.  Now, in light of developing metabolic and obesity issues in people, physicians are seeing the importance of this number, connecting with insulin levels.  They are now pushing for ideal fasting sugar or glucose levels in the range of 90-95 mg/dl.  Bottom line, their standards have been adjusted.

When it comes to insulin resistance in the horse, most are diagnosed when the levels of insulin rise above that 40 uIU/ml mark.  If they are below that number, they are not deemed insulin resistant and many veterinarians and even owners do not see them at risk of metabolic issues or even pasture associated carbohydrate problems.  In my practice, I see stages to metabolic disease in the horse and deem many of them as ‘pre-metabolic‘ and at risk of many health issues.  Many of my colleagues differ in this regard and some even do not recognize a ‘pre-metabolic’ stage in the horse.  It is certainly seen and recognized in human medicine, so why not in horses?  Why do we wait until that insulin level rises above 40 uIU/ml to take action?  If we did, could it lead to better outcomes?

I would venture to propose that the insulin normal values in the horse need to be re-evaluated and lowered.  I would further propose that a horse with a level of insulin around 20 uIU/ml is actually insulin resistant.  This is not hard to determine just by looking at the horse physically.  They often cannot be discriminated from the horse with a level of 45 uIU/ml, as both are overweight, have health issues, laminitis, and circulatory disturbances, not to mention thrush, white line disease and carbohydrate sensitivity. So, really, it is just a number that separates them, but that number is often what compels us to either take action or let things be what they are for now.  My point is that many of these horses are truly metabolic with insulin resistance, despite perceived ‘normal’ values.  They are being overlooked and therefore not acted upon appropriately.

Insulin Resistance in the Horse; A Bigger Problem?

Many of my colleagues do look at insulin:glucose ratios, which is helpful in some situation in determining if there is a problem.  While this is helpful, it still does not help us to see the larger population that is at risk.  The reality is that many of our perceived ‘normal’ and potentially non-overweight horses are at risk, but it is not diagnosed or tested for in the horse.  How about the average 3-day eventer?  The upper level dressage or jumper horse?  How about the average racing Thoroughbred?  Do they develop insulin resistance?  You bet they do! But when tested, often their insulin levels are ‘high-range normal’ and thus not deemed to be a problem.

In our facility, for the most part we are working with OTTB’s and their multitude of health and lameness problems.  Honestly, only until recently did I start to dig deeper, testing not just insulin levels but antioxidant and free radical loads.  Some of these horses have been on our supplements, yet still had lingering problems or issues that would come and go.  I’d scratch my head at times in the past. I’d culture feces initially, which many had major problems, then with a regimen the problem would be remedied on repeat cultures….yet, some still had lameness or health issues.

Then, several months ago, while testing metabolic and insulin resistant horses, I decided to start testing our OTTB’s with ongoing issues.  Interestingly enough, they shared some similarities with their metabolic and insulin resistant counterparts.

The average insulin resistant horse demonstrated an insulin around 90 uIU/ml or sometimes much higher.  The average OTTB for rehab would demonstrate an insulin level of 15-25 uIU/ml.  Then, look at blood glucose levels, which the metabolic horse with IR would average fasting in the upper 80-100 mg/dl, while the OTTB would not be far off from that value.

Now, let’s look at antioxidant and free radical loads.  Normal values here for sake of discussion would be around 250 for free radical levels (d-ROM) and >2500 for antioxidant loads (PAT).  The average metabolic and insulin resistant horse demonstrated a d-ROM of 182 and an antioxidant load of 1400-1800.  The OTTB had similar values, all a sign of generalized cellular hyporeactivity, which was discussed in part one of this article. The bottom line, in both groups of horses, their cells were not functioning correctly, which impacted not just insulin function, but cellular energy production, immune response, tissue health, and healing.  To the average horse owner and veterinarian, these OTTB’s would not be considered for insulin testing, but yet, it was playing a major role in their health.

Here is the interesting part, at least to me as a researcher and veterinarian.  In seeing the global problem of cellular dysfunction or hyporeactivity, I took a different approach with these OTTB horses that were in our facility for rehabilitation.  I took an approach to improve cellular function and with that, internal antioxidant generation and cellular REDOX balance.  As I took this approach, on repeat antioxidant and free radical level analysis, their levels dramatically improved, often just in 48 hours! Free radical levels (d-ROM) went up to 260 and antioxidant potential climbed to 3400 in most on fasting samples.  That is pretty incredible and now those levels are more in balance, more protective to the horse’s body, and yet, stimulating to the immune response.  All good!  The REALLY interesting part is that on repeat blood work in evaluating insulin levels in those same OTTB’s, their insulin levels often dropped to below or at 10 uIU/ml!

I did nothing directly to impact insulin in regards to medications or specialized low NSC diets.  All I did was stimulate the cell to function more effectively, regain balance, and improve internal antioxidant production.  As a result, the body naturally lowered the insulin levels.  This, at least in my opinion, raises the debate regarding our perceived ‘normal’ insulin levels in the horse.  If all is well and in balance in the horse’s body, my research experience tells me the insulin levels should be much lower than we think.  If I had to take a guess, I would put normal resting insulin levels in the horse at a range of 8-15 uIU/ml.  That is actually just a bit above what is perceived as normal currently in humans. This goes to show us that the average horse with an insulin of 25 uIU/ml may actually be insulin resistant and signal some significant cellular problems that are not being addressed.  Thus, we tend to put them on the back burner, adjust diet, and wait for the insulin levels to rise…which they will, and with that more health and lameness problems.

In Part ONE of this article, I mentioned that there were some concerning issues regarding this data of antioxidant and free radical levels as compared to 7 years ago.  In 2012, we did a pilot study involving some actively racing Thoroughbreds and gathered both d-ROM and PAT levels.  The data gathered from that group mirrored horses in our general practice at the time, with an average d-ROM of 240 and PAT level of >2500.  This was partly how we arrived at our normal values for the horse.  The alarming part is that 7 years later, the average horse has a d-ROM <200 and a PAT level of <2000. These levels are often found in the every day competitor or back yard pleasure horse.  This is concerning to me as a veterinarian, as it indicates a potential overall deterioration in the health of the horse, possibly due to contributors in the current diets and forages that are being fed, in addition to many sugar-loaded supplements and poor digestive health.  

Getting More Information About YOUR Horse

Insulin panels, leptin, and ACTH levels are important indicators in the horse.  There is no doubt, as when they are abnormal, they signal some problems, however we just tend to see isolated events and miss the bigger elephant in the room.  For me, personally, I test for insulin and usually do not go further.  The reason being is that I more so rely on antioxidant and free radical loads to indicate a real problem.  If insulin levels are high, then often this is reflected one way or the other in the d-ROM or PAT levels.  If these two are abnormal, then it would be no surprise to see an increased ACTH or Leptin.  In reality, most of these horses also have abnormal fecal cultures, so again, it is not surprising to see the connections.

Antioxidant and free radical load testing is not a part of normal laboratory work for the horse, nor even for humans.  The sad thing is that it is very valuable and actually very reflective and revealing of what is going on in the horse on a cellular level.  At this time, we do routine testing in all of our horses, along with fecal cultures, not just once but as a part of their recovery.  I view it as a gauge of fitness, health, and a measuring stick for recovery.  I don’t just implement a regimen and hope for the best.  I choose to monitor their recovery and make adjustments as needed.  Antioxidant and free radical levels are an indicator of oxidative stress and a marker of inflammation.  It gives you something to monitor and keep tract of regarding health improvement in the horse.  If you would like to have your horse tested, feel free to email me (

In PART THREE of this article, I will discuss exactly how we transformed the cell and encouraged it to function more effectively in the horse, which then impacted insulin levels and function naturally.


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

2 thoughts on “The Metabolic Horse; Digging Deeper into Insulin Diagnosis Part Two”

  1. I would like to know more about getting my horse tested. Other than frequent laminitic episodes he has none of the other ailments associated with IR.

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