Can the Damaged Insulin Resistant Horse be Fixed?

By Juliet M. Getty, Ph.D.

You’re worried. You have reason to be. Your horse is exhibiting signs of insulin resistance (regional fat deposits along the neck, down the spine, tailhead, shoulders, chest, or even above the eyes). He is likely overweight (though not always). You know that your horse is at a high risk of developing laminitis, and you want to avoid that at all costs. You’ve taken away the sweet feed, removed all cereal grains, stopped giving your horse carrots, searched on line for the latest supplement for treating insulin resistance, and put your horse in a dry lot. You’ve even found that perfect low sugar/low starch hay, carefully weighing it out each day to provide exactly 1.5% of your horse’s ideal weight. Doing this is difficult – you can’t bear seeing your horse so unhappy.

Your goal is to help your horse, not make him worse. A poor quality of life is not what you want for him. Feeding him in a manner that is contrary to his natural physiological needs is making his body scream for help. His hormones are raging. He doesn’t feel safe. To overcome this, he holds on to body fat, trying to protect himself from the perceived threats to his survival. You can see your efforts are not working.

Then you read my work about how important it is to calm down the hormonal stress response by feeding a low NSC hay, free choice. You decide to give it a try. Will it work for your horse? Very likely, yes.

The only way to fix your horse is to help him return to his natural state. However, the longer a horse lives as an overweight, stressed animal, the more difficult it is to bring that horse back to a normal weight, free of hypothalamic inflammation, with no more leptin or insulin resistance. In some cases the horse may have endured too many years of forage restriction, creating so much inflammatory damage, that time may have taken its toll; he may be too far gone. But the solution is not continuing down this destructive path; the solution is to try to make things better.

The current mode of thinking is to limit the horse’s hay intake and provide various forms of supplementation. But none of these supplements will make a significant difference if the horse is not fed in sync with the way he was meant to live. There are many research-supported reasons for this.

Deprivation actually increases insulin resistance

It is critically important that the horse have a steady supply of forage all day and all night. This is what is meant by “free-choice” – the hay never runs out, not even for 10 minutes. If it does, you put your horse in a state of fear. He fears an impending famine and his hormones will respond by keeping him overweight. Researchers at Louisiana State University found that mares having enough hay during the day but deprived of hay overnight showed the greatest degree of insulin resistance.[i]

Here’s something else that may surprise you. Your effort to control insulin by depriving your horse of forage actually works against you because glucose will eventually rise through the horse’s natural hormonal response. When a horse has nothing to eat, his blood glucose level starts to drop. He needs glucose to survive – it fuels his nervous system. In an effort to remedy the situation, the hormone, glucagon, is secreted to release glucose from glycogen stores in the liver. Glucose is also restored to normal levels by breaking down muscle. This lost muscle mass brings down the metabolic rate, and ruins his body condition.

Regional fat deposits develop. Fat deposits throughout key areas of the body (most typically along neck and shoulders) promote the formation of an enzyme known as HSD, which tells the body’s tissues to ignore insulin.[ii] More specifically, HSD leads to cortisol production, and cortisol, when elevated either due to body fat or by Cushing’s disease, leads to elevated insulin in the blood and ultimately, laminitis.[iii]

Body fat increases inflammation, leading to more body fat. Excess body fat secretes inflammatory substances known as cytokines.[iv]  Cytokines can damage the hypothalamus, the portion of the brain that recognizes leptin.[v] Consequently, leptin becomes elevated, but the horse does not respond normally be being satisfied. Instead, the horse keeps on eating, getting more obese, producing more cytokines, increasing inflammatory damage to the hypothalamus, resulting in greater leptin resistance, and more body fat.

Stress elevates cortisol. A prominent study at Ohio State University[vi] revealed that cortisol rises when horses experience an empty stomach for hours as they anticipate their next meal, or when they are bored or stressed in any way. This study emphasizes the exact reason that stress creates a cascade of events that damages the horse.

Stress affects behavior. Some horses appear calm and stoic about their discomfort. That’s a survival mechanism since the sick horse will be left behind in a wild setting. Some horses suffer openly and will behave erratically, have a poor attention span, and will act ornery. The suffering is both physical and mental.  

All that stress is totally unnecessary!

Here is a fascinating study.[vii] Fourteen obese, laminitic horses (of various breeds) were subjected to a specific management program that emphasized a mineral-balanced, low non-structural carbohydrate (NSC) diet,  along with daily exercise, specialized hoof trimming and sole protection. While hoof mechanics is not the scope of this article, diet certainly is. All of these horses were fed a low NSC hay, ad libitum (that means, free-choice!) and hand-walked (as long as they were able to walk with the hoof landing heel-first). The result – the horses went from a Henneke body condition score[viii] of 8.5 down to a score of 5.0—in other words, from obese to a normal weight!  And, after two years of grazing on pasture, all but one of them were able to continue on pasture while remaining sound!

I’m here to offer you what the ideal situation looks like. I ask you to do your very best to get as close to it as possible. Take a look at the details and see what you may have been missing.

Forget about the drylot without a steady supply of forage

Unfortunately, putting your horse in a dry lot with restricted hay will likely bring about another laminitis episode. Your horse may lose weight, but his body will be more inflamed than before. His metabolic rate will become exceedingly sluggish. Furthermore, leptin resistance will not been solved, telling the horse to eat more. Not being able to eat creates a cortisol surge, leading to an insulin surge and bingo! You have another case of laminitis.

Get aggressive in reducing inflammation

Removing stress is the first step, but the horse will still be leptin resistant because of the residual hypothalamic inflammation. Prepare to boost the diet with antioxidants, anti-inflammatory herbs, key minerals, and the right balance of omega 3s to 6s, preferably from supplements that provide wholesome ingredients, without the use of added preservatives. Removing sugar and starch from the diet, as well as chemicals that are often added to feeds, will reduce inflammation and the oxidative stress it creates. Please review articles[ix] in my website’s library for specific ways to accomplish this.

Balance minerals

Magnesium, copper, zinc, chromium, iodine, and selenium can impact insulin resistance. Magnesium is well known in its ability to impact glucose homeostasis, but many horses do not receive enough, either through inadequate dietary intake or from competition from calcium. Many forages, especially alfalfa, are high in calcium relative to magnesium; therefore, magnesium should be supplemented to bring the calcium to magnesium ratio down to 1.5 to 2 times more calcium than magnesium. Determine the level of calcium in your supplements – they could be making the ratio worse.

Watch out for excess iron. It has long been known that iron exacerbates insulin resistance in humans and laboratory animals, and it has been recently revealed to do the same in horses.[x] Since forages (pasture and/or hay) generally contain a substantial amount of iron, it is critical that it be balanced with other copper and zinc.[xi] Choose a vitamin/mineral supplements that does not contain iron. And avoid commercially fortified feeds that contain added iron. If you grow your own hay, or have a good relationship with your hay producer, check the soil’s pH. Grasses grown in acidic soils tend to accumulate more iron than those grown from alkali soils.

Offer a variety of protein sources

When only one source of protein is fed (such as one type of grass hay), there will not be enough variety of amino acids to provide good quality protein and many amino acids will go unused. Excess amino acids cannot be stored for later; they get destroyed in the liver and may be converted to glucose, potentially increasing insulin in the same way that sugar does.

Limit or eliminate stalling

Horses need to move. Ever tried staying in a small room for most of the day? And we like cozy places! Horses do not! Their very survival depends on their ability to flee at a moment’s notice from dangers, real or perceived. Trapped, most eventually yield to their fate, appearing as though they are accepting and perhaps even appreciating their solitude. But the stress eventually leads to a vast variety of health issues, including laminitis.

Exercise and just plain movement are critical to your horse’s well-being. Researchers at the University of Queensland, Australia[xii] demonstrated that exercise improves insulin sensitivity and reduces cytokine production. Leptin resistance has also been shown to improve through physical activity.[xiii] And from this we know that the insulin receptors on the surface of the cells are increased by exercise and that allows insulin to return to normal. And exercise doesn’t have to be formal. Researchers at Virginia Intermont College[xiv] found that pastured horses were just as fit as horses who were kept in stalls and exercised five days per week.

Don’t neglect the hindgut (cecum and large colon)

Its microbial population is responsible for digesting the fiber in your hay and pasture, producing volatile fatty acids which are a significant energy source. These microbes also produce B vitamins and other nutrients. In addition, the majority of your horse’s immune function is in the hindgut, preventing the overpopulation of detrimental organisms. Many horses benefit from prebiotics (fermentation products and other “food” for existing microbes) when shifting from one feed source to another, or during short periods of stress, such as travel or performing.

Probiotics contain live organisms. To be effective, your supplement must contain billions (not millions) of colony forming units (CFUs). However, use probiotics judiciously. Horses who are pasture grazing may not require them because they obtain microbes from the ground. But according to Tom Schell, DVM, the overuse of  Lactobacillus strains, which are often found in commercial feeds and supplements, may lead to an overgrowth of lactic acid producing bacteria, resulting in cecal acidosis and endotoxin-related (not endocrine-related) laminitis.[xv]

Free choice is less expensive

Feeding your horse all the hay he wants may appear to be costly. But in actuality, it is less expensive to allow your horse to tell you how much he wants because a horse who is permitted to self-regulate his intake will eat only what his body needs. Yes, he will overeat at first, but soon thereafter he will get the message that the hay is always there and he will start to walk away from it to take a nap or visit with his companions.[xvi] His eating will slow down and he will eat less, perhaps even less than he did before.

To ease the horse through the process, slow down his intake

Horses in a natural setting do not eat large amounts at one time; instead, they graze on small amounts of forages, walking great distances to find that next tasty morsel. Domesticated horses don’t always have large expanses of land to explore; therefore, it is up to their owners to make an effort to simulate the slow pace of natural grazing. Hay should be offered in small piles or in slow feeders in many locations to encourage movement and natural seeking behavior. If your horse is stalled, you can place a slow feeder net or container (choose one that does not damage the teeth or soft tissues) inside the stall in two locations. And always keep them full! These are designed to stimulate saliva flow and satisfy the horse’s need to search and pull hay from the openings.

A grazing muzzle offers a means of allowing the horse to enjoy some pasture time with his buddies. I am not in favor of using them for any length of time (no more than 3 hours) simply because the horse’s digestive system relies on forage flowing through it at all times. Furthermore, grazing muzzles can be very frustrating for some horses, leading to a hormonal stress response, and hence, defeating your purpose. But, if your horse is calm about having it on, it can be a temporary solution as you work toward improving your horse’s metabolic health. Keep in mind that the muzzle must allow for water drinking and drain properly. And never cover the openings with duct tape, as I have seen suggested; it is not only cruel, but dangerous.

Can your horse return to pasture grazing?

Yes, preferably if you test your pasture. Researchers at Louisiana State[xvii]  looked at horses who were fed hay in a dry lot versus those that were able to graze on pasture. Even though the NSC level in the forage was the same and the amount consumed was the same, the horses on the dry lot were more insulin resistant than the horses on the pasture. This had to do with the fact that the pastured horses were able to move around more and were less stressed than those on a dry lot.

What’s more, many horses who are confined to a dry lot with free-choice, appropriate hay, still have problems with insulin resistance, as well as overall health and condition. Deprived of fresh grasses can result in trace nutrient imbalances that cannot be easily corrected through supplementation. Moreover, horses who are accustomed to grazing effortlessly, interacting with other horses, and moving about, will exhibit stress-related responses when suddenly confined to a space that doesn’t allow them to enjoy behaving naturally.

Interestingly, horses who graze on pasture 24/7 will eat far less grass than those who are only allowed to graze on pasture for a few hours each day, with hay provided the rest of the time. Researchers at North Carolina State University[xviii] found that horses will typically consume 0.75 pounds of hay (dry matter) per hour when permitted access to pasture all the time. However, horses who only have 3 hours of pasture grazing time, will eat nearly three times more grass per hour.

If your horse is currently in a dry lot with hay and not doing well, and you have access to pasture (especially one which has a variety of plants, is not over-grazed, heat or drought stressed), you may want to consider gradually switching him from a dry lot to pasture, over a 3 week period. Start in the early morning hours when the sugar/starch level is at its lowest.

Bottom line

We are harming our horses by not letting them be horses. If your insulin resistant horse has endured years of being fed forage intermittently throughout the day, while waiting for hours for more hay, he is damaged. The good news is that there is every reason to feel confident that he will return to a healthy state. There are some horses, however, who have so much damage that they cannot recover. But you have no way of knowing that. The goal is to try to make things better. When you keep moving in the right direction, you will allow your horse to enjoy his life and strive toward regaining his health.


[i] Lestelle, J.D., Earl, L.R., Thompson, Jr., D.L., Hebert, R.C., and Mitcham, P.B. 2011. Abstract: Insulin-glucose dose response curves in insulin sensitive and insensitive mares and effect of overnight and long-term feeding regimen. Journal of Equine Veterinary Science, 31, 285-286. Louisiana State University Agricultural Center. 

[ii] Johnson, P.J., Ganjam, V.K., Slight, S.H., Kreeger, J.M., and Messer, N.T. 2010. Tissue-specific dysregulation of cortisol metabolism in equine laminitis. Equine Veterinary Journal, 36(1), 41-45. College of Veterinary Medicine, University of Missouri at Columbus, Missouri.

[iii] Getty, J.M., 2013. Laminitis. A Scientific and Realistic Approach. ISBN: 978-1483956169.

[iv] Wisse, B., 2004. The inflammatory syndrome: The roles of adipose tissue cytokines in metabolic disorders linked to obesity. Journal of the American Society of Nephrology, 15(11), 2792-2800.

[v] De Git, K.C., and Adan, R.A., 2015. Leptin resistance in diet-induced obesity: The role of hypothalamic inflammation. World Obesity, (16(3), 207-224.

[vi] Saul, J.L., Nyhart, A.B., Reddish, J.M., Alman, M., and Cole, K. Effect of feeding practice on glucose, insulin, and cortisol responses in Quarter Horse mares. Journal of Equine Veterinary Science, 31(5), 299-300. The Ohio State University. 

[vii] Taylor, D., Sperandeo, A., Schumacher, J., 2014. Clinical outcome of 14 obese, laminitis horses managed with the same rehabilitation protocol. Journal of Equine Veterinary Science, 34(4), 556-564.

[viii] The Henneke System was developed by Don R. Henneke, Ph.D. of Tarleton State University in Texas in 1983.  The Henneke System is a consistent method of objective evaluation of a horse‘s body condition based on visual and palpable fat cover over set points on a horse.

[ix] Getty, J.M. "Obesity. The Real Cause. The Real Fix.", as well as, "PPID Progression can be Slowed Down,"  "The Overweight Horse Who Won't Stop Eating. Leptin Resistance in the Key! " 

[x] Nielsen, B.D., Vick, M.M, & Dennis, P.M. 2012. A potential link between insulin resistance and iron overload disorder in browsing rhinoceroses investigated through the use of an equine model. Journal of Zoo and Wildlife Medicine, 43(3), S61-S65.

[xi] Getty, J.M. "Too much iron can be detrimental to the insulin resistant horse."  

[xii] Pollit, C., de Laat, M., van Eps, A, Baldwin, G., Underwood, C, Medina-Torres, C., and Collins, S. 2011. Advances in Laminitis Research at the Australian Equine Laminitis Research Unit. Journal of Equine Veterinary Science, 31, 569-571. University of Queensland, Australia.

[xiii] Flores, M.B.S, Fernandes, M.F.A, Ropelle, E.R., et. al. 2006. Exercise improves insulin and leptin sensitivity in hypothalamus of Wistar rats.  Diabetes, 55(9), 2554-2561.

[xiv] Graham-Thiers, Patricia M, Bowen, L. Kristen. 2012. Improved ability to maintain fitness in horses during large pasture turnout. Journal of Equine Veterinary Science, 33, 8, 581-585.

[xv] Schell, Tom DVM, 2015. Fecal microflora and dysbosis; Contribution to metabolic syndrome, inflammation and leaky gut syndrome

[xvi] Getty, J.M. 2013. The Easy Keeper. Making it Easy for Him to be Healthy. 

[xvii] Lestelle, J.D., Earl, L.R., Thompson, Jr., D.L., Hebert, R.C., and Mitcham, P.B. 2011. Abstract: Insulin-glucose dose response curves in insulin sensitive and insensitive mares and effect of overnight and long-term feeding regimen. Journal of Equine Veterinary Science, 31, 285-286. Louisiana State University Agricultural Center. 

[xviii] Glunk, E.C., Pratt-Phillips, S.E., and Siciliano, P.D., 2013. Effect of restricted pasture access on pasture dry matter intake rate, dietary energy intake, and fecal pH in horses. Journal of Equine Veterinary Science, 33(6), 421-426.

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