The Skinny On Low-Starch Diets

Specialized feeds have helped horses cope with health challenges for many years.


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Specialized feeds have helped horses cope with health challenges for many years.

On the market now are low-starch products, but experts say not every horse will benefit from them.

Mary Beth Gordon, Ph.D., director of research and new product development for Purina Mills, says top-performing horses require a higher level of soluble carbohydrates in their diet.

“Racehorses, for example, have to be able to replace glycogen quickly because of their work,” she says. “Studies show the best way to do that is with a moderate to high soluble carbohydrate grain.” 

Brian D. Nielsen, Ph.D., PAS, Dipl. ACAN, a professor of animal science at Michigan State University, says the majority of horses probably encounter few, if any, problems when consuming a feed higher in starch.

“Mature horses that are fit, have a thin or moderate body condition score, and have a high energy demand likely can consume a high starch diet with absolutely no problems,” he says.

Specific Conditions

Studies have shown that low-starch diets are most beneficial in horses suffering from equine metabolic syndrome, insulin resistance, Cushing’s syndrome, PSSM (polysaccharide storage myopathy) and laminitis.

“Diet is key [with these conditions],” says Lori Warren, Ph.D., PAS, of the Equine Nutrition Institute of Food and Animal Agriculture at the University of Florida. “It’s all about finding alternative sources of calories, getting away from starch as a calorie source and moving toward more highly digestible fibers. PSSM horses fed low-starch diets usually show a relatively quick improvement. Low-starch diets for the others mentioned are really more about maintenance, so the diet won’t aggravate the condition.”

Formulated Diet

Warren says there is no universally recognized definition of starch.

“It varies individually by nutritionist or feed company, but typically the more traditional sweet feed, heavily based on corn and oats, is 40 to 60 percent starch,” she says. “It can be quite high, but for the vast majority of horses this is perfectly fine. When we get down to the midlevel range, which is usually called ‘controlled starch,’ typically that’s in the 20 to 24 percent range. Low-starch might be less than 12 or 13 percent. And so there is a very dramatic difference.” 

Ingredients can include chopped or pelleted timothy or alfalfa, beet pulp, soy hulls and rice bran. Fat sources such as corn and soybean oil can be added to increase the calories. “This is important if you have a PSSM horse that’s still performing,” Warren says. “You need to add calories back in.” 

Science is behind the low-starch diet, and none has been more peer-reviewed than Purina’s WellSolve L/S. After completing six years of research and two published articles in the Journal of Equine Veterinary Science, Purina took the diet to the market in 2008. Though Purina already was selling low-starch feed, horse owners wanted something specific for “special needs” horses. 

“The last thing the horse world needs is more products that don’t work, so I said it would have to prove it’s better than low-starch diets we already have,” says Purina’s Gordon. “It had to be measurable, and we needed to test it in horses with conditions, laminitis, Cushing’s syndrome and insulin resistance.”

Gordon’s team evaluated digestible/fermentable fibers as energy sources, Omega-3 and Omega-6 fatty acids, protein types and quality (amino acid profiles), antioxidants, key vitamins, minerals and feed form. She also considered how meal size and hay affected insulin and glucose response.

“We were able to develop a formula with lower insulin response than Ultium and Horse Chow. So we had a product that would work.”

A low-starch diet can be tailored. “I’m working with a Grand Prix dressage horse who has a history of laminitis and has been on WellSolve L/S and has been stable for several years,” Gordon says. “But he doesn’t have enough zip, so we were able to do a glucose tolerance test in the field, and we know the diet is working as it should. We feel comfortable his insulin is under control, and we can give him some more starch.”

Low Glycemic or Low Starch?

Horse people often want to compare the low-starch diet to the popular human low-glycemic diet, but the two aren’t the same.p>

The low-glycemic idea comes from human nutrition and is not generally interchangeable with the low-starch diet, says Mary Beth Gordon, Ph.D , of Purina Mills. I've found there's so many factors involved that it's difficult to get a handle on an equine diet with a low GI. What do you compare it to? We don't feed horses potatoes or white bread. So the diet is called low-starch in the equine world.

Hay Only?

Michigan State’s Nielsen says owners can get too wrapped up in the issue of what to feed their special-needs horses.

“Realistically, you can just feed your horse roughage. He probably doesn’t need grain. There are many horses out there living just fine without any supplement. And horses with issues like we are discussing probably aren’t doing too much work anyway.”

But Gordon prefers to err on the side of caution.

“There’s a huge variation of hay and it’s difficult to get consistency,” she says. “I definitely think hay should be the basis of the diet; the more quality forage the horse eats, the better the digestive health. But you need to be able to balance out that forage with something. If your hay or grass is low in protein, you’re not going to be meeting the amino acid requirement.” 

This article first appeared in the March 2010 issue of Veterinary Practice News.

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