Safe Grazing for Horses with Metabolic Issues



It's that time of year- days are warming, grass is growing, and the horses are impatient to get turned out to go nibble it!  Grass is the most natural food for horses, but fresh grass can be your worst enemy if you have an insulin resistant (IR) horse. Known as Equine Metabolic Syndrome (EMS), insulin resistance presents a special challenge when it comes to grazing. Let your IR horse gorge on grass unchecked, and you may have laminitis or a serious case of founder on your hands. In this blog, I share my personal experience with my IR mare Tess, some little known botanical facts about grass, and my best practices for grazing my IR horse.

Insulin resistance equine metabolic syndrome.jpg

Fat Tess and Fit Tomax

My mare Tess is a quintessential cobby Andalusian/Arab cross mare. Even on her skinny jean days she is round and shapely, the Mae West of the horse world. I have considered more than once re-naming her Hoover. All she does is stand around and eat. In contrast, my gelding Tomax (who passed away in 2014 at ripe age of 27) was at the opposite end of the eating spectrum. A good self-exerciser, Tomax would pick at his food all day.  On his “fat” days, he looked more like a fit horse. I kept Tess and Tomax in the same dry lot, which made the comparison between the two even more obvious. 

After one winter several years ago, Tess started resembling a beach ball and seemingly overnight developed an impressive stallion crest. Alarmed, I had blood drawn with fingers crossed. Now here is the interesting thing; Tess didn’t test positive for IR or Cushings, although she had suspicious looking fat pads over her neck, shoulders, and tail head.  I put her on a strict diet and increased her exercise. She slimmed down by about 250 pounds and was back to her J-Lo shapely booty.

Trust Your Gut

Over the years, I kept tabs on Tess’s endocrine system via blood tests. Despite rigorous management, and keeping her near target weight, she slowly developed the true clinical signals of insulin resistance. By the time Tess was sweet sixteen, it was clear she was IR. Throughout the series of blood tests she never foundered, and her weight fluctuated, but she just had the look of insulin resistance. The look included a crest and fat pads on her ribcage and by the tail.

Take home message: trust your gut. Blood tests don’t always have the answer as it can take years for clinically detectable disease indicators to develop. In addition, Tess never tested positive for hypothyroidism. The general protocol of putting her on Thyro-L without a blood test, a popular thing to do in some places for overweight horses, would not have been the answer. 

Grass Can Be Like Candy for Horses

Horses love grass for the same reason we love donuts, it’s sweet and full of sugar. In grass, the main sugars that the plant uses for energy are called fructans. Fructans are produced during photosynthesis during daylight hours and stored for use during the night [2, 3]. Fructan concentration in the grass can vary greatly depending on type of grass, temperature, moisture, and season [2, 3]. Cool season grasses found in areas with cold winters are especially strong fructan producers. Heavy rainfall, like that experienced in tropical climates, can flush out fructans and reduce sugar content.

In general, fructan levels spike in grass due to the following environmental conditions [2]:

1.       When there are low nighttime temperatures and warm day temperatures.

2.       When there are bright, sunny, warm days where plants are photosynthesizing.

3.       When the plants are in the active growing stage.

4.       When there is hot, dry weather.

5.       Anytime the plant is stressed, like by overgrazing.

Grazing your IR horse when grass is high in fructans is like feeding a Type 2 diabetic a candy bar.  It causes a spike in insulin, which can have a variety of negative effects. One serious consequence is the vasodilation (dramatic expansion in the blood vessels) in the laminar tissues of the feet, or laminitis. This means blood can pour into the feet quicker than it can be pumped back out.  However, it is important to note that signs and symptoms may not be immediately apparent. A laminitic episode can occur more than a week after a bout of overgrazing [1]. Sweets like bananas, apples and carrots have a similar effect. Even natural sugars can have a profoundly toxic effect in the body of an IR horse.

laminitic hooves laminitis founder.jpg

How I Manage My IR Horse

1. Monitor Your Horse's Digital Pulse

BEFORE there is a crisis, learn to take your horse’s resting digital pulse (this is the pulse down by the feet). All horse owners should know what their horse's "normal" digital pulse feels like. Click the blue link above to see our video on taking the digital pulse, or ask your vet to help you find this. Feeling the pulse “tone”- pressure, strength is as important as the actual count. A strong bounding pulse (which could indicate the potential onset of laminitis) may not be dramatically faster, just much stronger. Ideally, the digital pulse should be faint and almost hard to notice.

2. Introduce Your Horse to Grass Slowly

When I lived in the Northern Rockies, I kept my mare Tess off the grass until it was past its early growth stage and before it overly matured. I also made a chart where I would hand graze starting at 5 minutes and add 5 minutes a day to a max of 4 hours if there wasn’t any circumference increase in her neck crest. A horse can be fit and still have regional fat deposits that are indicative of metabolic issues. In this case, go by the condition of the crest/tail/shoulder fat deposits, NOT whether you can feel the ribs. My Montana vet recommended 20 min hand grazing only on grasses not actively photosynthesizing- thus early morning or after dark. The rest of the time, I kept Tess kept in a dry lot. Tess loves grass, but staying sound is more important.

3. Time Your Horse's Turnout

I never graze Tess between ten am and seven pm. Research [2, 3] shows that on bright sunny days in northern latitudes, sugar levels in the grass peak in the late afternoon around six pm, since the plant has had all day to photosynthesize. I get up early and turn out, often around six am. I bring my horses in before nine am.  If mornings are difficult, I try to turn out at least two hours after dark- once fructan levels are down.

4. Exercise Your Horse!

My veterinarian believes that regular exercise is just as important for controlling IR symptoms as regulating feed intake. My IR mare also has ringbone, so I can’t work her too hard. I do my very best to do some vigorous trot work on straight lines 3-4 times per week to get her into a serious sweat. Unfortunately, life and work happen, and I’m not always able to ride. Hand walking at brisk pace is an alternative, or lunging with lots of transitions.

5. Hay Is for Horses

I feed hay often, and in small-hole hay nets. I also weigh my hay every day.  I have a set up that makes this easy, but again, it’s a daily chore that I choose to invest in for the well-being of my mare. Tess strictly gets 15 pounds of food, broken up over three-four feedings. The small hole nets keep her trickle feeding longer than loose hay, so that we can work to avoid hind gut dysbiosis or gastric ulcers. These conditions can occur when horses go long periods of time without forage. (we discuss indisdious hind gut conditions in our online course on Equine Nutrition, which you can find HERE). With horses that have insulin resistance issues, or have foundered, it is also ideal to soak the hay in fresh water for 20 minutes prior to feeding to help leach out the fructans. If you do this, make sure you change the water with each soaking. 

What to Do If You Board Your Metabolic Horse

Approximately 80% of my clientele board their horses and thus are beholden to the barn management’s routine. Discuss with your vet about what is most appropriate for your horse, then approach the barn management to seek a solution. If turn out times cannot be altered, a grazing muzzle can be used to cut down on grass intake. While most horses dislike the muzzle, they will eventually grow accustomed to it. Particularly mischievous ones may even figure out how to nibble a lot of grass through the muzzle.

To Graze or Not to Graze- that is the Question

Yes, it is a pain managing your IR horse’s grazing regime. However, preventative health measures are preferable to chronic laminitis, or a severe founder that could permanently cripple your horse. Your horse has management costs whether they are sound or lame, so it’s preferable to keep them sound. I have a very busy schedule, but I still choose to manage my horse’s grazing. To grass or not to grass--- it comes down to protecting your IR horse’s long term health.

insulin resistant horse.jpg

About the Author

April Johnston is the founder of Equine Equilibrium and Co-Founder of the Equi-Librium Institute, an online school which helps horses by educating their people. A former resident of Florida and Montana, she currently resides in Kailua-Kona, Hawaii where she is Chief of Staff for her mare Tess, small feathered dragons Beetle, Ziggy and Binky, her dog T-bone, cat Charcoals and her husband Mark.


1. HOFFMAN, Rhonda M. Carbohydrate metabolism and metabolic disorders in horses. R. Bras. Zootec. [online]. 2009, vol.38, n.spe, pp. 270-276. ISSN 1806-9290

2. LONGLAND, A.C.; CAIRNS, A.J.; HUMPHREYS, M.O. Seasonal and diurnal changes in fructan concentration in Lolium perenne: implications for the grazing management of equines pre-disposed to laminitis. In: EQUINE NUTRITION AND PHYSIOLOGY SOCIETY SYMPOSIUM, 16. 1999, Raleigh, NC. Proceedings... Raleigh: Equine Nutrition and Physiology Society, 1999. p. 258-259

3. LONGLAND, A.C.; BYRD, B.M. Pasture nonstructural carbohydrates and equine laminitis. Journal of Nutritionv.136, p.2099S-2012S, 2006 (suppl.)