Hay for the Laminitic Horse

Q. Is there a particular type of grass hay that is better than others as a long-term part of the maintenance diet for a horse prone to laminitis?

Sue, via e-mail

A. If a horse has a history of chronic laminitis, my first concern would be addressing the metabolic issues contributing to the problem, usually obesity and/or pituitary dysfunction, both of which are treatable.

If the horse is truly insulin resistant/glucose intolerant there is no one "type" of hay guaranteed not to trigger a bout of laminitis. It depends more on the harvest conditions, not the species of grass, as to whether a batch of hay contains sufficient non-structural carbohydrates (NSC: starches, water soluble sugars and fructans) to cause a problem. Most horses tolerate more than 20% NSC without adverse effects, and most grass hays, especially those from the Eastern states, contain only 7-18% NSC, with an average of 12%. Even legume hays, on average, contain less than 15% NSC. Oat hay, on the other hand, averages 22% NSC. (Values are based on five years of data from Equi-Analytical Laboratories' web site.)

Some people are recommending that insulin resistant horses not be fed hays containing over 10-12% NSC. If in doubt or dealing with a very sensitive horse, get the hay tested before feeding it.

Grasses accumulate NSC throughout the day, with the highest concentrations achieved late in the day if the sun is shin-ing. If temperatures are above freezing and adequate water is present, NSC are converted to cellulose and other structural carbohydrates overnight, resulting in very low sugar concentrations by daybreak. If this process is disrupted by drought or freezing temperatures overnight, NSC concentrations can increase significantly.

The grasses continue to "respire" after cutting until the hay is baled and "cured." The longer the hay is dried in the field, the lower the NSC will be. Sugars and fructans are water soluble, so if the hay is rained on (or soaked in water), the overall NSC will also be reduced. "Warm season" grasses, such as coastal Bermuda and crabgrass, tend to accumulate lesser amounts of sugars than the "cool season" grasses like fescue, orchard grass, and timothy under adverse conditions. Some accumulation will still occur if the conditions are right. Be aware that most horses are not adversely affected by this variability in pasture grasses or in hays!

If a horse really is sensitive to NSC content, the "safest" hays would be coastal Bermuda or timothy cut early in the day, after a warm night and recent rainfall. Hay dried in the field for at least a day or two--even rained on a bit--is considered safer (i.e., first or second cutting, depending on the year, from the Eastern states). Western hay producers tend to cut their hay later in the day to prevent excessive drying, and they bale more quickly than is possible in the humid East, all of which tends to preserve the NSC content.

About the Author

Sarah Ralston, VMD, PhD, Dipl. ACVN

Sarah L. Ralston, VMD, PhD, Dipl. ACVN, is a professor in the Department of Animal Sciences at Rutgers' School of Environmental and Biological Sciences, specializing in equine nutrition. Her research has focused on the effects of diet on metabolism, behavior, and the development of orthopedic disease in young horses, and she has additional interests in nutritional modulation of stress, metabonomics (the study of metabolic responses to drugs, environmental changes, and diseases), and pasture management. Previous research highlights were the pioneering work she did in nutrition for geriatric horses and post-surgical colics while at Colorado State University in the 1980s and the discovery of the correlation of hyperinsulinemia with development of osteochondrosis in young Standardbreds.

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