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Purina nutrition experts remind horse owners to use caution on spring pasture

by Wyoming Livestock Roundup

“If we have pasture and intend to utilize it for horses, there are some things to consider,” says Karen E. Davison, an equine nutritionist and sales support manager at Purina Animal Nutrition.

“During this time of year, as pastures come out of winter dormancy, their photosynthesis activity greatly increases,” comments Katherine Williamson, manager of veterinary services at Purina Animal Nutrition.

As a result, spring grasses have a high concentration of sugars.

Spring grass

“Grass contains numerous different types of sugars depending on the species,” notes Williamson.

Excess sugars are stored in grass as starch and fructan.

“Simple sugars, starch and fructan in plants are referred to as non-structural carbohydrates (NSC),” she explains.

Warm season grasses, such as Bermuda grass and crab grass, store extra sugars as starch, and cool season grasses such as timothy grass and fescue typically store extra sugars as fructan.

“NCS concentrations are highest during late spring, cool temperatures, bright sun and late afternoon,” she adds.

Switching from winter

Because many horses are coming off of winter feed schedules, these high concentrations can be a shock to their digestive systems.

“Going from dry hay and grain to lush, green pasture is a drastic change in diet and may increase the risk of founder, also called laminitis, or colic,” explains Davison.

As green grass comes up, horses kept in the pasture full time will become accustomed to it.

“Horses that haven’t been on green grass should only be allowed to graze for an hour or two at first,” she adds.

Every few days, the grazing time should be increased by an hour, until the horse is on pasture full-time, according to Davison.


“When horses consume grass, starch is digested to glucose by enzymes in the small intestine and absorbed,” Williamson comments.

If the concentration of starch is too high, the small intestine might not be able to absorb it, in which case it can overflow into the hindgut.

“If the amounts of fructan and starch reaching the hindgut are large, a shift may occur in microbial populations, favoring lactic-acid producing organisms,” she continues.

This can change the internal chemistry of the horse so that toxins and other substances flow into the blood stream where they can be carried to the hoof, causing founder.

“Individual horses will have different tolerance levels to diet change and the nutritional profile of grass,” states Davison.

She suggests feeding horses with dry hay before they are turned out, so that they are not overly hungry when they first see new spring grasses.

“Horses that are obese or insulin resistant due to disease appear to be more susceptible than those with more moderate body condition or normal insulin sensitivity,” notes Williamson.


Williamson comments that pasture-associated founder may be harder to prevent than it seems.

“Limiting access to pastures during periods when NSC levels can be expected to be high is ideal,” she says. “However, for many horse owners, this may not be practical.”

Mowing pastures, building partitions, grazing horses in shady areas and using grazing muzzles are some of her suggestions for horses that may be susceptible to founder.

“Pasture time is certainly a plus when it comes to managing happy, healthy horses but not all pastures are created equal,” adds Davison.

She recommends consulting with a local horse pasture and forage expert, such an Extension specialist or university agronomist.

“Some pastures provide a significant source of nutrition while others are just a place to play,” she says.

Davison encourages horse owners to manage for the nutritional requirements of their animals, taking special precautions during seasonal transitions.

These steps, she says, “help to maximize the safety and value of available pastures.”

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be contacted at

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