Interpreting hay analysis results
Carbohydrates - WSC, ESC, Starch, and NSC
Horses on hay-based diets may get more than 80% of their daily energy needs met from the microbial fermentation of complex carbohydrates in the large intestine. (This process generates small organic acids, called 'volatile fatty acids', that the horse converts into long-chain fatty acids or glucose, as need be.)
The starches and sugars in grass hay contribute relatively less in a caloric sense, but their contributions to obesity, laminitis, colic, and exercise-related muscle disorders can be far greater. For this reason, we pay these 'hydrolyzable' and 'rapidly fermentable' carbohydrates a great deal of attention, particularly when selecting hays for overweight, laminitis-prone horses.
Other horses who may fall into the category of 'carbohydrate-sensitive' include those with equine polysaccharide storage myopathy (especially Quarter Horses and related breeds, and draft breeds), recurrent exertional rhabdomyolysis (especially Thoroughbreds and Arabians), equine systemic proteoglycan accumulation (a hallmark of which is suspensory ligament degeneration), equine Cushing's disease, and recurrent colic.
Before we go on, please open this chart summarizing the different types of plant carbohydrates (it should open in a separate window) and refer to it as needed. It really does help keep all these bits & pieces straight.
Of the four separate 'carb' results reported for this analysis, I'm most interested in these:
Water-Soluble Carbohydrates (WSC) include the simple sugars (mono- and disaccharides), oligosaccharides (including fructo-oligosaccharides, or FOS), and fructan polysaccharides. As starch is low in most grasses (typically less than 3%, and often less than 1%), it's the WSCs that cause the most problems in grass hays. For carb-sensitive horses of any type, I like the WSC content to be less than 10% (as sampled).
(When you factor in the water content, that translates to a WSC of around 11% Dry Matter. You'll often see recommendations for at-risk horses of less than 10% WSC (Dry Matter), which translates to less than 9% WSC as sampled. This 1% here-or-there may seem like splitting hairs, and perhaps it is; but many of these overweight, laminitis-prone horses are living on a knife-edge, and such details can mean the difference between developing laminitis and not. That said, I can tell you that I've seen no problems with using an upper limit of 10% WSC as sampled; and as I'll discuss in a moment, there are distinct advantages to gracing your horse with a hair more WSC - along with other nutrients.)
Nonstructural Carbohydrate (NSC) content is simply WSC + Starch. In most grass hays, adding Starch to WSC doesn't change the figure all that much (in this timothy hay, for example, it adds only 0.4%). However, according to Equi-Analytical's database, the Starch content in grass hays nationwide ranges from 0.3% to 7% (as sampled), so it's a simple calculation that's well worth making, because it could really matter.
Furthermore, many nutritionists and veterinarians talk about the NSC content when discussing how to feed at-risk horses. A common recommendation for overweight, laminitis-prone horses and ponies is to feed a hay that has a NSC of less than 10% (Dry Matter). I have some problems with that recommendation:
1. Poor palalatability - that's a selling point for this "cardboard" diet, but in my experience it greatly increases hunger, discontent, and the incidence of potentially disastrous escapes onto fresh grass - real food!
Suggested limits for carb-sensitive horses.
2. Poor digestibility - such a low NSC goes hand-in-hand with a high ADF; not only does that increase the risk for impaction colic (not even the gut microbes can do much with this hay!), it practically guarantees malnutrition, and although it may not be as severe as frank starvation, it greatly impedes recovery.
3. Inadequate crude protein - often the protein content is too low to meet the horse's maintenance needs when healthy, let alone when recovering from laminitis or dealing with metabolic syndrome (which I find is very responsive to careful protein supplementation).
Managing carb-sensitive horses is a topic for another time. Suffice it to say that I want the NSC for healthy horses with no special needs to be no more than about 15% - so that they don't become at-risk horses, for whom I want the NSC to be less than 12% (as sampled) [or less than 13% Dry Matter].
Nonfiber Carbohydrate (NFC) content is less useful to me, both from a medical and a nutritional standpoint. It just doesn't give me much more information than the WSC and NSC provide.
Its primary use to me is as a quick 'eyeball' measure of whether or not the hay is going to be safe for a carb-sensitive horse. I want the NFC content for an at-risk horse to be between 12% and 15% (as sampled). In my experience, that's a happy medium between medically safe and nutritionally adequate - which includes palatable and satisfying. For a health horse with no special needs, the NFC can be as high as 20% (as sampled) without any problems.
Carbohydrates - WSC, ESC, Starch, and NFC