Q: When looking for safe hay for equids diagnosed with insulin dysregulation (ID) or pituitary pars intermedia dysfunction (PPID, formerly known as equine Cushing’s disease), I look for low ethanol-soluble carbohydrates (ESC) and low starch values in hay; so why does soaking hay to remove water-soluble carbohydrates (WSCs) make hay safe to feed these metabolic animals? Although I do soak hay for my PPID/ID horse religiously to prevent him getting sore feet/laminitis, it’s never made sense to me—ESC and starch could still be high. –via email

A: Instead of looking at just ESC and starch levels of hay for your horses with issues such as ID/PPID, it is valuable to consider all carbohydrate fractions in that forage. However, carbohydrate fractions can get complicated. Historically, the term nonstructural carbohydrate (NSC) was commonly used, but it is important to understand that nonstructural carbohydrates include WSC + starch. Water-soluble carbohydrates are directly measured via extraction in water and contain ethanol-soluble carbohydrates + fructans. Ethanol-soluble carbohydrates are simple sugars and, because simple sugars have the greatest impact on blood glucose and insulin concentrations following a meal, ESC often is more of a focus for owners of horses with insulin dysregulation.

Fructans are the storage carbohydrate of cool-season grasses and are resistant to enzymatic hydrolysis (a digestive process in which macromolecules are split from food by the enzymatic addition of water) in the small intestine but are rapidly fermented in the hindgut. You can calculate the approximate fructan level by finding the difference between WSC and ESC. It is important to avoid high fructan levels in forage for horses with a history of laminitis because it can put them at a greater risk of a laminitic episode.

Sugars and fructans are water-soluble carbohydrates and, as the name implies, are leached from the plant when exposed to water. There have been several research studies investigating the effects of soaking hay on soluble carbohydrate content. When comparing the effects of soaking hay across these studies, soaking reduced both the WSC and ESC values, although the results were quite variable for both depending on the base forage, water temperature, and the time allowed for soaking. Based on these findings, horse owners should be consistent with soaking methods and, ideally, should send off a soaked hay sample for analysis to determine the most ideal soaking method for their hay.

The general recommendation for ID/PPID horses is a diet low in NSC (<12%), although the data does not support a hard line on this value. When developing a feeding program for these horses, you should start by getting your hay analyzed. If your hay is already below 12% WSC + starch, then there is no reason to soak; however, if the hay tests higher than 12%, soaking can be a good way to reduce both WSC and ESC values.