You Can’t Always Follow Your Gut With An IR Horse

Following your gut instinct is good advice in some situations but gut, and even good old common sense, can also be wrong.  This is where fact and science come in.

Correctly caring for a horse with insulin resistance takes some major lifestyle changes. It is up to the caretaker to implement those changes. This can be a major advantage for the horse, who doesn’t have to rely on his own will power, or it can throw any number of obstacles in his path.

We hear things like ‘The horse can’t possibly be happy without pasture’, despite the fact that millions of horses around the world are; many of which do not even have pasture as an option. Another is that they can’t possibly be healthy on a diet restricted in amounts or types of food, when in truth it is the human imposing their own emotional reaction to that possibility on the horse.

Most dangerous are objections that sound like they are based in science when they are not. One is that not permitting an IR horse 24/7 access to food will cause stress and a cortisol increase that will actually make him worse.  This has a ring of truth to it, but it’s wrong.

Sticker et al 1995 fed mares either 100% of requirements or restricted calories by 50%.  The restricted mares had a drop in cortisol levels.

DePew et al 1994 fasted mares and stallions for 19 hours then fed a pellet and hay meal. Cortisol rose after feeding and did not change in response to fasting for 19 hours.

Glunk et al 2015 fed adult Quarter horses a restricted hay diet of 1% of their body weight either as loose hay or from slow feeder nets, divided into two feedings with 15 hours between the afternoon and morning  meals.   The floor fed horses finished their meals much quicker.  There was no difference in cortisol levels between the two types of feeding. Cortisol dropped in both groups over the 28 day trial despite the markedly restricted feeding and weight loss. [Horses were sampled every 30 minutes after meals and hourly between feedings.]

Storer et al fed both normal and hyperleptinemic (IR) mares either constant pasture, free choice hay or hay and pellets only once daily.  The mares fed only once daily had an expected exaggerated insulin and glucose peak after feeding but their cortisol levels were lower than the mares with constant access to hay or pasture at all testing times.

Freestone et al 1991 did find small (but not statistically significant) rises in cortisol in ponies fasted 24 to 72 hours, consistent with the tendency of ponies, but not horses, to develop exaggerated release of fat into the bloodstream with fasting. The metabolism of ponies (and minis, donkeys) is distinctly different from horses.

What about the fact that feral horses spend 18 to 20 hours a day eating? This observation does not automatically mean horses have to spend this much time eating to be metabolically healthy.  You have to remember that grass is over 70% water while hay is typically around 10% and a much more concentrated calorie source than pasture.  They have to spend that much time eating native pasture to get enough calories.

By all means feed your insulin resistant horse with a slow feeding set up to avoid long gaps with no food that might lead to insulin peaks and also just to keep her busy but don’t worry that going without food for even short periods will increase cortisol and make IR worse. Research has proven that’s simply not the case. In fact, in study after study a drop in cortisol has been found with fasting or restricted feeding of horses.

Eleanor Kellon, VMD


About Dr. Kellon

Graduate of University of Pennsylvania Veterinary School. Owner of Equine Nutritional Solutions,, industry and private nutritional consultations, online nutritional courses. Staff Veterinary Expert at Uckele Health and Nutrition.
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16 Responses to You Can’t Always Follow Your Gut With An IR Horse

  1. Dr. Kellon says:

    You don’t have to mow off the seed heads. The grass will drop the seed within about 10 days. Yes, the mature grass that remains has the lowest sugar and starch levels. Don’t worry about soaking depleting the hay. Protein does not soak out. Only sodium (very low anyway), potassium (always high) and sugar soak out to any significant extent.

  2. Alison says:

    Excellent! Just what I needed to hear! Thank you.

    • L. says:

      Any idea how cortisol levels and hindgut organisms are affected if the horse turns to eating manure during times of reduced feed? In addition to use of a slow feeder, do you have suggestions of how to minimize the problem in a paddock?
      Since I took my IR mare off pretty-much-free-choice grass hay a few months ago, my horse has been eating manure quite a bit (though I’m thinkng she might also have other nutritional issues going on that contribute to the issue. I’m sure her worm load is greatly increased, at the least.)

      • Dr. Kellon says:

        Have you heard of fecal transplants? It’s the placement of “donor” fecal matter into a patient with intestinal disease. Vets have been transplanting fecal matter into horses by stomach tube for many years. It’s a harmless way to give a blast of probiotics and has no effect on cortisol. Slow feeder nets with holes as small as 1/2 inch are available and these can be doubled up – whatever you need to do to make the day’s supply of calories last longer. Toys like the Nose It which dispense hay cubes can also help. If you suspect a nutritional issue you best action is to have you hay analyzed and supplement accordingly. Several species eat manure when protein is insufficient. Keeping manure picked up throughout the day is the best parasite control but don’t guess about parasites. Test her.

  3. Lucy says:

    Thank you so much! It is so refreshing and reassuring to read an article based on research and fact instead of unsupported opinion. I almost killed my fatty (but not IR) horse with the free-choice low everything hay.

  4. Elizabeth Yensan says:

    My IR horse is currently on a large dry lot. The hay I have now is what you would call “low quaility” ESC 4.5 starch 0.6 WSC 5.8 protein 9.6. If you know you have low sugar hay is it ok to give them free choice in that case? It seems like pretty low quality to restrict intake. Thank you.

    • Dr. Kellon says:

      Low quality doesn’t just mean low sugar and starch. Your protein level is good and if fiber fractions are ADF 40% or lower, NDF 60% or lower with no mold or heavy dirt, weeds, it’s still a good quality hay. Free choice does depend on calorie level. You could use your horse’s daily calorie requirement to figure out how much hay you would need to feed to meet it. If what the horse consumes voluntarily over 24 hours is in that neighborhood, try free choice feeding.

  5. L. says:

    Thank you so very much for sharing all this information! It will be very useful for me as I’m making decisions about how to help my IR mare lose weight!

  6. Liz Nichols says:

    Hi Dr Kellon
    I have read in the past that horses should have constant access to safe food to avoid microorganism death in the hindgut. I realise you are not advocating fasting but just wondered whether this aspect was studied in the fasting trials.

    • Dr. Kellon says:

      It would have to be an extreme fast indeed to have a significant effect on organisms in the hind gut. Food remains in the hind gut for an average of 48 hours. Fasts of 24 hours, even extreme starvation conditions, do not produce signs of hind gut disruption and while you may have decreased total numbers these will rapidly rebound when the horse eats.

      • Liz Nichols says:

        That is great to know, thank you. I have always worried about having my IR horse without food for any length of time, He is actually a hard keeper so weight is not an issue for him but I am glad to know that if he does have small periods without access it won’t cause him any long lasting health problems 🙂
        Thanks Dr Kellon!!

  7. Regina Bruno says:

    I’m just learning about this…so, while this article is about cortisol, is it also safe to interpret that what you are saying is it’s okay if an EC/IR horse isn’t constantly nibbling on some low starch/sugar something or other? One of my horses has a lameness and can’t be exercised and i want to start keeping him in the stall while i’m at work, which is usually for anywhere from 6 to 8 hours. If fed an appropriate diet, is it ok for him to be “fed” or “snacked” (sometimes just a flake of hay) 2 or 3 times a day? They can seem a little pumped after being kept in for 8 hours (they aren’t used to it) but I have a “gut” instinct that this is actually good for them as long as I am sure they don’t gorge themselves when I get home….? Another misguided gut?

    • Dr. Kellon says:

      There’s nothing inherent wrong with some stall time with hay while you’re at work, even if he runs out before you get back to feed him again. I would caution you though that if he was formerly worked regularly the rest period will probably result in insulin resistance worsening so you will have to be careful about amount and type of food. Also, if your pasture has matured and gone to seed this is the safest (no guarantees) time to graze. However, it has been documented that horses kept off grass for part of the day will make up for it by eating more and faster when they do have access. You will have to watch him carefully.

      • L. says:

        Question about grazing a pasture that’s gone to seed:
        Is it correct that a high percentage of grasses’ NSCs are transferred into seeds, so IR horses shouldn’t be grazed on it until seeds have been mowed off? But then the grass that’s left has had a large part of its NSC level depleted, so it’s ideal for grazing then?
        Also–Thank you very much for your counsel on my mare’s manure eating!!
        I just started her on probiotics, and will look into deworming & slow feeder helps, too.
        Her hay tests to have 10.35% protein, but I’m soaking most of it, so probably depleting.
        I’m also planning to post a more comprehensive picture of her case in the ECIR group & see if there are additional elements that need to be addressed.

  8. Ruth says:

    Can I ask what your thoughts are on the possibility of stomach ulcers in a horse that is fasted? Many thanks, Ruth

    • Dr. Kellon says:

      First, I want to make it clear I was not advocating fasting – just showing it does not lead to a rise in cortisol.

      It takes a minimum of 4 to 6 hours for a meal to completely exit the stomach and small intestine, 2 hours of which is time spent in the stomach but this is also highly variable and even horses not fed for 12 hours are often found to have residual food in their stomachs when examined with an endoscope. I can tell you that researchers attempting to induce ulcers by fasting have found that it takes 4 days of alternating periods of 24 hours fast, 24 hours fed to reliably result in ulcer formation.

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