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Insulin Resistance (IR)

Insulin is a hormone secreted by the pancreas.  It signals the insulin sensitive cells (in skeletal muscles & fat) to take up glucose from the blood. All sugars and starches in the diet are converted to glucose before being absorbed.

Insulin Resistance is not a disease per se, but more of a type of metabolism. As of this writing, information points to a genetic basis for insulin resistance. Easy keepers such as arabians, morgans, mules, donkeys, ponies & miniature horses seem to be more prone to IR. While IR has often been compared to diabetes ...it's not the same. In equine IR the insulin levels are high but the glucose levels remain within normal range. In human diabetes the blood sugar is elevated and depending on the type of diabetes (type I or type II), the insulin levels can be low or high. For some reason, horses do not appear to progress to actual diabetes as easily as other species do.

To determine if your horse is insulin resistant, you want to get a non-fasting glucose/insulin from the same blood draw. It is important that it be a non-fasting draw because when we are dealing with an IR horse, we want to know what a typical meal causes in the way of a glucose & insulin rise. Feed either low sugar/starch hay or soaked hay  (not a grain meal) 2-4 hours before the blood draw. A horse that is fasting will have a much reduced glucose & insulin, some insulin levels will appear absolutely normal. We don't want to know what the insulin level is on an empty stomach but rather what the insulin rise when there is food to digest.

Once you have these results then you can calculate the insulin: glucose ratio. Your insulin & glucose results need to be in the proper units to determine this ratio.  Insulin in IU/L or U/L and glucose in mg/dl. Some labs use different measures. If your insulin results are in pmol/L divide this number by 7.1 to get IU/L results. If your glucose results are in mmol/L multiply this number by 18 to convert to mg/dl. Once you are in the proper units simply divide the glucose by the insulin number. A number below 4.5 is considered Insulin Resistant.
Too complicated? Or you can use this handy-dandy on-line IR calculator:
http://www.freil.com/%7Emlf/IR/ir.html

Symptoms of IR
While not all overweight or obese horses are IR, that is one of the earliest symptoms. Development of prominent fat deposits on the crest of the neck, at the tail base, along the withers or at other locations is also common. Sometimes geldings will have swollen sheaths.
Advanced cases of IR will display increased thirst & increased urination (polydipsia/polyuria) and lethargy. Skin & respiratory allergies are also common in IR horses. Keep an eye on those easy keepers! Occasionally, thinner horses can also be IR as in my late Tamera's case; although I'm sure her IR was a result of advanced Cushing's.

IR horses and ponies are at high risk for developing repeated problems with laminitis and it has been acknowledged that IR is a pre-disposing factor to laminitis. The exact mechanism for the laminitis is unknown, but likely related to the circulatory and inflammatory changes that are known to go along with IR in other species.  Over time this can develop into life threatening cases of founder.

Managing Insulin Resistance
The only way to manage IR is through strict diet & regular exercise. Feeds high in non-structural carbohydrates (NSC) should be avoided. Here at Shotgun Ranch we avoid any feed that has a higher sugar/starch level than 10%. We have our hay analyzed and only buy hay that have sugar/starch levels below 10%. Beet pulp (when properly rinsed/soaked/rinsed) is an ideal carrier of supplements for the IR horse because it produces an almost undetectable glycemic spike. In larger amounts beet pulp is also the safest way to put weight on an underweight horse.
I usually add a handful of tested (low sugar/starch) pellets to their supplements as well. In the beginning some horses are not too enthusiatic about beet pulp, but herbs such as peppermint, calendula, spearmint, chamomile, etc. can be added to spice up their low sugar/starch meal.
Treats such as carrots & apples & many store bought horse treats are high in sugar (mostly because they use molasses as a binder) & will cause a glycemic spike & should of course be avoided.
Some safe treats include, iceberg lettuce, celery & squash. Small amounts of apple peelings are okay too.
At  this time the only company that makes a tested & guaranteed low sugar/starch treat is Skode's Horse Treats
http://www.skodeshorsetreats.com/
Although I bake my own horse treats in many different flavors. I often buy some of Skode's Treats baked cookies or a ready mix as a back-up in case I don't have time to bake my own.


The Importance of Testing Hay

While it is true that soaking hay is a good way to lower the sugar level in the hay, it must be done properly. The hay must be totally submerged for ½ hour in hot water or 1 hour in cold water and then drained somewhere where the horse does not have access to the water. Soaking the hay in this manner can lower the sugar (ESC) level up to 30%. The key word here being... the sugar (ESC).
You need to know & remember that no amount of soaking will lower the starch level. If your hay has a high starch level, soaking will do no good what so ever.
I learned this lesson the hard way back in March of 2008.

Thunder, our little Morgan has always been an easy keeper & always stayed trimmer when being exercised regularly.  Even though his weight fluctuated, he never seemed to have any other problems, that is until March of 2008. The end of February that year, we ran out of our yearly supply of bermuda hay and bought a small stack at the local feed store to tide us over until our regular supplier's first cutting. I did test the hay but really didn't look at the results too closely since I had decided not to balance the minerals, as I only considered this to be an interim hay until we could get our yearly supply from our regular supplier.  By the end of March, Thunder was overweight, lethargic, drinking & urinating excessively and stumbling. He could not stay in a trot for more than 8-10 strides. Even though in my heart I knew Thunder was IR, I was still dealing with Doc's (our Quarter horse) lameness issues & had turned a blind eye to Thunder's cries for help. Finally, on April 28th,  I took a good look at Thunder & had our vet out thereby confirming Thunder's Insulin Resistance. Thunder's insulin was 171.3  (lab range 5-20) & his glucose was 111mg/dl  (lab range 60-120). His G:I ratio was 0.65 with an RISQI of .08.
His status was: severe IR, with a high laminitis risk.
I was racked with guilt, how could I have ignored all these symptoms?
But no time to beat myself up...it was time to act.
That day I started soaking hay for all three horses....I saw no improvement in Thunder after one week of soaking. How could this be? Suddenly, the light bulb went on & I went though my files and looked at my hay analysis.  The starch level was 9.0% ...no wonder I saw no improvement. Soaking will not lower starch & you can only soak out 30% of the sugar. I knew this! My sugar & starch level was 12.4% and by soaking it I was only lowering the level by 1% at the most.That same day I sold that hay to a neighbor & got a new batch that had a sugar level of  8.1% & starch 3.8%. By soaking this hay I could conceivably lower the levels to 9.5%. So, I continued the soaking routine. Within 2 days Thunder's stamina improved drastically.
The pictures below tell the story...


Thunder on 3-20-08, overweight,  lethargic, dull & lifeless
coat from lack of mineral balancing.

 On 6-2-08 after one month on low starch soaked hay, 20 minute lungeing 5 days a week & minerals balanced to his hay.


7-7-08 One month later,  lungeing at liberty, shiny, sleek & full of pep.

When I look at these pictures & realize how close Thunder was to coming down with laminitis, I thank my lucky stars for opening my eyes when I did. It is so easy to turn a blind eye when you feel overwhelmed & have too much on your plate already.
The important thing is not underestimate the importance of a low sugar/starch diet in an Insulin Resistant horse.
Today, no hay comes through our gate unless it tests below 10% in sugar/starch, not only for Thunder's sake but for Doc our PSSM horse & our sweet donkeys as well.


Gus, one of our donkeys is IR as well. In this photo you can see the classic IR fat pads.
Even though he has been on a low sugar/starch diet since he has been with us, his fat pads have stayed about the same....well, maybe a little smaller...but not much. I believe that losing those fat pads is a slow process. However, his coat has become much softer due to the 2 ounces of flax in his diet. I'm also starting to see better hoof quality due to the trace mineral balancing & added biotin in our custom mineral mix.
Donkeys are hardy little creatures designed to survive in the harsh & sparse conditions of the desert therefore making them easy-keepers (there's that word again.)
Internal parasites are the #1 killer of donkeys, so like horses they require a parasite control program. They also have the same mineral & vitamin needs as horses. Our donkeys are fed the same minerals & vitamins as our horses, just in ½ of the amount.


About Pasture
Whether IR horses should be allowed on pasture is a subject of great controversy.
I think it depends on the animal, the severity of their IR (any laminitic history), the pasture conditions & the time of year.
We only have ½ acre of bermuda grass, it is very sparse & poor quality but a good psychological exercise.
I would venture to say that they are lucky to consume a pound of grass during several hours of nibbling.
Now our back yard is a different story, it's lush & thick and I could see where they could eat 1 pound in a matter of minutes.
They are never allowed in our backyard unless someone forgets to put the clip on the gate & Doc declares it "partytime" and lets everyone out. Luckily that rarely happens & we've always been right there to escort them back to their home.

I was very fortunate that our Cushing's/IR mare Tamera  was able to enjoy pasture time with no complications.
As of this date, Thunder who has never had laminitis or displayed any foot soreness has access to pasture with no problems (knock on wood). But remember, he most certainly reacted to that high starch hay.
Gus has limited pasture time with no problems, but I'm always checking for pulses & increased heat in his hooves or any change in his IR symptoms, such as changes in the texture & size of his crest & fat pads, increased drinking/urination, etc.

So... my advice is be careful. Has your horse ever had laminitis? How severe are his IR symptoms? What about lab values?
If you feel your horse's IR is under control & he is getting regular exercise, you might start with 15 minutes of grazing & watch him carefully....keep your eyes open.

About Hoofcare

I'm not going to get into a lengthy discussion about barefoot vs. shod horses.
Although my horses have been barefoot since 2001, if a situation warranted shoes, I would not hesitate to shoe my horse. If there is one thing I have learned in 40 years of owning horses, it is "Never say never!" However, like with anything else, there are good farriers and there are incompetent farriers. Our responsibility is to recognize the difference. A properly shod horse, starts with a properly balanced trim.
We as horseowners need to educate ourselves. Learn what a well-trimmed, healthy, balanced hoof looks like.
Learn to recognize: long toes, underun heels, contracted hooves, overlaid bars, balance issues, over-grown frogs, false sole, etc.
Even though I'm not a trimmer, I'm not afraid to use a rasp or even a hoof knife when needed in between my horses' regular trims.


References/Resources
While some of the information you read here comes from personal experience, most of  my opinions have been influenced  by the  many years of membership in the Equine Cushings group. The group's files & message archives are a veritable treasure of cutting edge information. If you have an IR horse I highly recommend you join this list. It could save your horse's life.

http://pets.groups.yahoo.com/group/EquineCushings/

Dr. Kellon's excellent on-line courses are invaluable for anyone who owns or works with horses:, she even has a "Cushing's & Insulin Resistance" course

  http://www.drkellon.com 





Updated 9/03/09