Cutting Down on Carbs (For Your Horse)

In an attempt to avoid the rich diets that can worsen obesity and laminitis in insulin-resistant horses (those said to be suffering from peripheral Cushing's disease), many owners feed hay instead of lush pasture or grain. However, Kathryn Watts, BS, director of research for Rocky Mountain Research and Consulting, has found that some hay isn't a safe diet for insulin-resistant horses, and in fact some hays could be much worse than one might think. But she has had success with an easy, very inexpensive way to make hays safer.

Watts presented a poster on her research findings at the Second International Equine Conference on Laminitis and Diseases of the Foot, held in West Palm Beach, Fla., Nov. 10-11. Her focus was on the levels of water-soluble carbohydrates (sugars) in hay, which are powerfully affected by the weather conditions before hay is cut and while it dries.

"Sunny days combined with cold nights causes the sugars produced by photosynthesis during the day to accumulate when growth that occurs at night is restricted," says Watts. "Other factors that may increase water-soluble carbohydrates (WSC) in hay are drought stress, intense sunlight, nutrient deficiencies, high salt content of the soil, and very rapid drying of the hay. About the lowest-sugar hay you can get is hay that was rained on between cutting and baling."

Increased WSC, including the fructan that is often used to induce laminitis in the laboratory, is bad for horses which can't handle a rich diet. But how do you tell if your hay has too much sugar for your horse? Have it tested, says Watts--the look of hay is no indicator if its sugar content. Part of her poster included samples of various hay types from different areas of the United States. High-sugar hays included several different plants and different colors of hay; in other words, you couldn't select "good" or "bad" hay (in terms of sugar content) based on visual inspection.

Watts listed the following high, medium, and low-sugar/fructan grasses common to horse pastures based on USDA forage research on reactions to cold stress, and she offers this caveat: "Amounts will vary from one variety of grass to another, so this is just a general trend between species. It is entirely possible that if you buy hay from a state-of-the-art grower, he could very well be growing a state-of-the-art, higher-sugar variety. We cannot assume that a lower potential to accumulate sugar under cold stress will hold true under other types of stress. For instance, some really high-sugar native grass hays are showing up this year in the Midwest due to drought. When cut under optimum growing conditions, WSC in bromegrass hay can be suitable. We must always discuss WSC content in context with the environmental conditions in which the grass or hay was grown."

  • Potentially high sugar/fructan grasses--brome, any small grain hay (wheat, oat barley, rye, triticale), orchard grass, quackgrass, fescue.
  • Medium sugar/fructan grasses--crested wheatgrass, Garrison Meadow Foxtail, timothy.
  • Potentially lower sugar/fructan grasses--bermuda, big bluegrass, bluestem, crabgrass, many summer annual native prairie grasses, reed canarygrass, most warm-season C4 grasses.

Reducing Carbs in Hay

But how can you cut down on carbohydrates for your horse when the hay has already been baled? The answer is simpler than you might think. Remember those WSC--water-soluble carbohydrates--discussed earlier? Water-soluble means they dissolve in water: "Simple sugars, disaccharides, and short-chain fructan are soluble in cold water, while the longer-chain fructans are soluble in hot water," says Watts.

The question is: Can they be "pulled out" of hay when it is soaked?

"Fifteen samples of various kinds of hay, including straight alfalfa, alfalfa-grass mixes, straight grass of several varieties, and oat hay, were split into representative sub-samples," explains Watts. "These were tested for WSC content before soaking, after 30 minutes in cold water, after 60 minutes in cold water, and after 30 minutes in hot water. The range of WSC before soaking was from 4.4% to 34.4%. (on a dry matter basis)."

Think about that percentage--feeding your horse 20 pounds of hay with 34.4% sugar would mean he gets 6.88 pounds of pure sugar!

"All soaked samples were drained, dried at 60° Celsius overnight, and retested for sugar content," continues Watts. "The average amounts of sugar reduction after 30 and 60 minutes in cold water were 18.9% and 30.7%, respectively. The average amount of WSC removed in 30 minutes in hot water was 29%."

There was a wide range in the amounts of WSC pulled out of various hays--from 0% to 55.9%. Watts says more work needs to be done to define which hays don't lose much WSC by soaking, although there seems to be some correlation with the maturity of the hay. As for other nutrients that might also leach out of hay with soaking, she reports that potassium seems to be the only one lost based on preliminary work.

While researchers continue to search for a cure and better prevention for laminitis, it appears that soaking hay to reduce carbohydrate content might be one more weapon in preventing or managing laminitis in insulin-resistant horses. And as with all weapons, it should be handled with care.

"There are many factors that affect sugar and fructan levels in grass, and these factors may very well overcome any intrinsic lower levels of any one species of grass," says Watts on her web site, "Please do not think that if you plant the right kind of grass, your laminitic horse can now graze free-choice. You may lessen the chance of overdose on sugar, but you must still be on guard."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More