Most horses are fed too much energy these days. But it’s especially unhealthy if that energy comes from fructose, says Dan Undersander, University of Wisconsin Extension forage specialist.

“Cool-season grasses tend to store energy as fructans,” made of fructose molecules that can cause hindgut acidosis in horses, he says.

“And timothy, which has been favored by horse owners, is one of the highest fructan accumulators.” Tall fescue, orchardgrass and bluegrass also produce good amounts of fructans.

Smooth bromegrass, tall wheatgrass and meadow fescue are safer options, because they don’t accumulate as much, Undersander adds.

Horse diets need to change because horses today “are not working as hard as they used to. They don’t get as much exercise or use up much energy,” he says. To make matters worse, horses prefer the sweeter-tasting, high-fructan cool-season grasses.

But the right management can lower the amount of fructan in grasses.

For instance, manage grass hays for high yield, he suggests. “When hay is growing, it is lower in fructans because it uses the energy from fructans to grow. So what you want is a hay that is grown on a well-fertilized field that is managed for high tonnage.”

Also avoid cutting and feeding hay that has gone to seed. “A lot of people want to see a few heads in their timothy hay to prove that it’s timothy – it’s a very distinctive, cylinder-type of seed head.” But plants are highest in fructans when seed heads have formed, Undersander says. “If they were to harvest a little earlier, then it would have lower fructans.”

Cool-season grass hay harvested while growing rapidly, at moderate temperatures, is also lower in fructans. Drought-stressed grasses will contain more, he warns.

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Cool-season pastures also should be managed to avoid high fructan levels. Don’t turn horses out too early in spring, when fructan levels are highest. And don’t graze pastures with grasses that have already formed seed heads.

The time of day grasses are grazed is also important. “Fructans are highest in forage in the afternoon, so if they graze in the morning, they’ll have fewer fructans in the forage,” Undersander says.

Essentially, horses will eat healthier if their owners use the same grazing-height guidelines that cattle producers are supposed to use.

“Our standard grazing recommendation actually fits for horses very well. We’d like to see pasture over 6” tall when we’re grazing it, and it shouldn’t be grazed below 3-4”.”

To figure out if their grasses contain too much fructan, he advises growers and horse owners to look at the non-fiber carbohydrate (NFC) content of grasses, commonly found within most forage analyses. NFC includes sugars, starches, fructans and organic acids, he says.

“I asked the labs here in Wisconsin and in Georgia for the number of samples they have done on grasses. And the NFC from all labs ranged from about 2% to 35-40%. If they look for an NFC of, say 15% or less, that’s going to include the sugars, starches and fructans, but they know that at least all three are combined to a low value.”

Forages with NFC contents of 20% or more are suspicious. “If they want to buy a high-NFC hay, they could have it re-analyzed for fructans and see if the high NFC is due to starch or due to fructans,” Undersander says.

If the second analysis shows fructan levels at more than 10%, the grass hay may be too high in energy for a horse’s good.

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