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Sugar Content of Pasture & Hay: Q & A with Katy Watts, Founder of

Katy Watts is a leading worldwide authority on sugar levels in grass and hay and the conditions that influence them. She has a BS in crop and soil science from Michigan State University.

Katy worked as an independent contract researcher performing pesticide efficacy and residue studies and consulting for farmers growing potatoes and grain. When her horses experienced laminitis, she switched her focus to sugar content of grass and hay.

Over the next decade, she wrote articles in veterinary journals, conducted cooperative field studies with academics, spoke at numerous veterinary and nutrition conferences, wrote various book chapters and lectured worldwide. Katy is the founder of 

Read on to learn more about Katy's findings from her field studies in her plight as a plant scientist to better understand the factors that contribute to NSC (NonStructual Carbohydrate) levels in plants. 

Katy Watts, leading authority on the NSC content in grass and hay.tent
Katy Watts, founder of

First of all, what sparked your interest in studying equine diets?

​My vet was a small time breeder of horses.  He told me that supplements were a waste of money; that all a horse needed was good quality hay.  So I bought hay from the same grower that he did.  When my horses became very ill with laminitis and skin problems, I started testing my hay for everything to find out why.  The hay analysis showed deficiencies in trace minerals. I wasn’t aware of available testing for nonstructural carbohydrates at that time but I’m confident it was very high; it was cut in the late fall when nights are very cold. When I presented the analysis to the hay grower to inform him of the trace mineral deficiencies, he said, ‘”I supplement my cows with minerals.  Don’t you supplement your horses?” That’s when I realized I was on my own, and started buying equine nutrition text books.​

What are the main contributing factors to sugar levels in pastures?

​​Genetic potential triggered by amount of sunlight and a variety of plant stressors including: 
  • Cold temperatures
  • Nutrient deficiency
  • Drought stress  
Sugars accumulate in grass when there is abundant sunlight but factors limit growth.​​

What times of the day or night are “safer” to turn horses out on pasture given those factors?

When conditions for grass growth are optimum, sugar levels are lowest from about 3AM to 10AM. When nights are near freezing, or drought stress is ongoing, sugar levels stay high around the clock and sensitive horses should be removed from pasture.

What conditions create the lowest sugar levels in pastures?

  • Foggy, cloudy weather with nights above 40F
  • Optimum levels of nutrients and moisture with management to prevent heading. 
These conditions result in the amount of sugar per bite of grass at its lowest levels; however, caution is still warranted if the horse has the opportunity to overeat. ​​

What conditions pose the greatest risk for higher sugar content in grass?​

  • Sunny days and nights with freezing or near freezing temperatures
  • Abundant sun and drought
  • Nitrogen deficiency

​Do the same principles apply when cutting hay? 

Yes.  Unfortunately very few horse owners have direct contact with hay growers so they can discuss the weather before cutting.  This is why testing your hay is so important. I’ve asked my audiences if they would pay $5/ton extra if hay lots were tested for nonstructural carbohydrates and they all agreed. Hay brokers and growers are missing out on a value added concept if they don’t have tests for NSC available. 

​What species of grasses do you recommend when planting lower sugar pastures?

​There is no standard answer as it will depend on climate, soil type, management and the sensitivity of the horses being fed. The only grasses I have found to always be low in sugar are difficult to grow, low yielding and require intensive management. It’s easier to say avoid ryegrass, fescue, timothy, clover, and high sugar weeds.

What test results do you consider as a sum for NSCs (NonStructural carbohydrates)?

​The definition of NSC is not under consideration by plant scientists, but is a firm definition.  It is the carbohydrates found in the nonstructural (internal) portions of a plant cell as opposed to structural carbohydrates found in the plant cell wall.  The best approximation is provided by adding water soluble carbohydrates (WSC) and starch percentages. It’s only vets and nutritionists that quibble over how to add it up (WSC + starch or ESC + starch) and what portions have nutritional relevance to horses.

Why do vets and nutritionists quibble over what percentages to use as a NSC sum? 

​The nutritional relevancy of ESC vs WSC has not been researched due to the unavailability of fructan from grass in a pure form.  All the studies implicating fructan in laminitis, insulin response, and gut pH have been done on fructan sourced from broad leaf weeds.  It is very different, being shorter and more prone to rapid fermentation.  Hence the uncertainty of the effects of grass fructan on horses and whether ESC or WSC is more relevant. For sure, fructans from broad leaf weeds are bad.

What are the definitions of Starch, ESC and WSC?

  • Starch: a polysaccharide found primarily in the grain or seed and/or root portions of plants.
The two most common methods for measuring the sugar content of hay and pasture are the ethanol soluble carbohydrate (ESC) and the water soluble carbohydrate (WSC) methods.
  • ESC: captures monosaccharaides, disaccharides, oligosaccharides, and a small fraction of fructans. 
  • WSC: captures all of the ESC components + the remaining fructans.

​Do you recommend grazing muzzles or slow feed hay bags/nets? 

Absolutely!  Some grass and hay is too nutritionally dense for pleasure horses with efficient metabolisms.  In order to prevent them from becoming obese, forage must be restricted. Muzzles and slow feeders stretch out the time it takes to eat that limited forage. It enables them to eat for a longer time but with smaller bites.

​How do you determine if you should test your hay?

I’d like to say everyone should test their hay, but it’s not always practical and less important on average for healthy horses, especially when the source of hay changes frequently.  Hay testing is like insurance, with the benefits weighing against the risks.  It’s more important to special needs horses with metabolic challenges or brood mares and young growing stock. If you have an equine with metabolic issues such as EMS, PSSM, or HYPP, testing hay is essential because the sugar and starch content of some hay can cause serious medical consequences.​
Young stock are more prone to problems involved with mineral deficiencies and imbalances.  In that case, if a person always fed a ration balancer (formulated by a qualified equine nutritionist), feeding untested hay would have less risk. ​

​What are the benefits of testing your hay?  

You know what you are feeding. As above, the horse you are feeding is a factor in determining risk/benefit.  If you have metabolically normal horses, and stumble onto a hay with very high digestible energy and they gain weight, the consequences may not be disastrous.  If you are observant, you will observe the weight gain and decrease the amount fed.  Frankly, I would rather test all hay to insure it’s not rocket fuel.

What do you consider an ideal diet for horses that are metabolically challenged? 

The best hay I found was native grass, similar to a feral horses diet, but it’s hard to find.  For a few years I fed blue gramma grass hay that a farmer was growing for seed but it became full of weeds and he had to plow it up, even when I begged on my knees! Then I had bluestem (sometimes called prairie hay) trucked to Colorado from eastern Kansas.  Both of these native grasses always tested very low in sugar and my ponies could eat it free choice. It sure made my life easier, and they didn’t eat manure or weeds.  Other good choices are Teff and Bermuda, but I have found some can be higher in sugar and starch, so I recommend testing before purchase. Find out if horses Can Eat More Hay Without Weight Gain. The Surprising Factors

​Overall - My preference is for equine guardians to provide hay free choice that is not more than 0.9 Mcal/pound DE and less than 10% NSCs singling out horses that require additional calories daily for supplemental bucket feed. This allows for all horses in the herd to live together and get plenty of chew time; keeping something in their stomachs around the clock.  

​Do you have any closing thoughts?

The term ‘easy keeper’ is really a misnomer.  Horses that are metabolically challenged are far more difficult to keep.  I rescued a pony once with her backbone and hips sticking out, and SHE was easy to keep.  I let her graze on the good pasture my ponies could only have 2 hours/day for 24/7 and 3 months later, she was looking good.  Today’s improved grasses, developed to fatten cattle more efficiently, make hay choices for pleasure horse owners with efficient metabolisms very difficult. Those of us who have managed a horse prone to laminitis will never consider buying hay an easy task again.  Prevention is WAY easier and cheaper than a cure.  


To learn more about Katy's extensive research & field studies, visit


"Our little mini is a chronic colic and founder case.  We have struggled tremendously to keep her healthy.  We have implemented a "track" style to our paddock, very little to no grass and 4 Hay Pillows placed on each side of the paddock.  The two of them move each other between the hay pillows all day, encouraging and aiding digestion and increasing circulation to the all-important hooves.  We've tried several other more expensive products, but yours work the best! Thank you!" ~Mandy~

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Monique Warren, Hay Pillow Founder with the Hay Pillow Slow Feeder product line - standard ground hay pillow, mini hay pillow, hanging hay pillow & horse trailer manger hay pillow

About the Author

Monique Warren invented the Hay Pillow® slow feeder and is the owner of Hay Pillow Inc. ​Warren has been an equine guardian for over forty years and slow-feed advocate for over 10 years. She contributes equine nutrition, digestive and hoof health articles to publications such as Equine Wellness, The Journal, The Naturally Healthy Horse, Natural Horse Magazine, Nicker News, The Horse's Hoof and Miniature Horse World Magazine. Equine nutrition and horses feet are her passions. She resides in Southern California.

Monique's Story

1 Comment

  • The best article and research I have seen
    I have a one year old filly who suffered with Epiphysitis
    And if I had read this article I do not believe this would have happened.
    It was too late already when we realized the grass hay we were feeding was so high in sugar.
    I now have a horse that will have a long recovery .

    Elaine Simon

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