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