Decoding Hay Assays

Written By Walt Friedrich

Carbohydrates -- such simple things, yet they can seem so complicated. Since our horse is a hayburner, his hay is the first place we look when we want to know what kinds of carbs and how much of each he’s getting. So we have a hay sample assayed – a simple, inexpensive procedure – to get a picture of what the hay contains.
But then, when we look at the numbers on the assay report, we find it’s a real struggle to dope out what they all mean. It may not even mention the word, “carbohydrate”. For example, the carbohydrate portion of a typical hay assay report looks something like this:
                                                                   Dry Matter              As Sampled              Basis                                                                          Basis
% Acid Detergent Fiber                        33.7                          37.1
% Neutral Detergent Fiber                  54.6                          60.1
% Lignin                                                  4.7                             5.2
% NFC                                                    15.1                           16.7
% WSC                                                     5.9                            6.5
% ESC                                                      4.2                            4.7
% Starch                                                    .7                               .8
Ouch!
We assume the answers are there, but it’s pretty complex. We have a challenge on our hands.
Let’s try to simplify things a little here, to at least get you started.
The types of carbohydrates, and where they are digested
While there is much information on an assay report, we’ll be discussing only carbohydrates, leaving the rest of it for another time. Lest we confuse you, in general, when we speak of carbohydrates as regards our horses’ diets, we’re actually talking about various forms of sugar, and we’ll occasionally be interchanging the terms here.Understanding the assay report is not rocket science. For our purposes, here's how simple it actually is: carbohydrates can be divided into those which are easy-to-digest and those not-so-easy-to-digest. The assay tells us how much of each type the sample contains. We’ll get to why it’s important in a moment.

Easily digested carbohydrates (simple sugars) are assimilated in our horse’s small intestine -- early in the digestive system. Harder-to-digest carbs (more complex sugars) need to reach his large intestine, where he gets some digestive help from the billions of permanent-resident microbes living there, symbiotically. They get paid for their efforts by partaking of the feed itself.
Got it? To understand it, all we need to concern ourselves with are simple and complex sugars, and where in the digestive tract they are assimilated. The assay report tells us about the former, and nutritionists have told us the latter.
Sugars are vital, but sometimes can be dangerous
Consider a healthy horse with a properly functioning digestive system: as long as he gets regular exercise we don’t have to worry much about his diet, provided it’s appropriate and he’s healthy. As with you and me, an appropriate diet and enough exercise leads to good health.
But we know that we need to be picky about hay if our horse is laminitic or prone to it, or is insulin-resistant, either condition potentially leading to founder. And, of course, if our horse is healthy to begin with, we want a well-balanced hay, one which won’t contribute to the onset of such problems. Sugar is at the heart of these conditions, and the assay tells us what we need to know to prevent them.
What are the carbs on the assay, and which are most important?
It contains a lot of numbers, but we are interested only in those that report carbohydrate content, and fortunately for us, most labs group all carbohydrate-related readings together on the report. There are only a handful; here they are, again:
Acid Detergent Fiber (ADF)
Neutral Detergent Fiber (NDF)
Lignin
Non-Fiber Carbohydrates (NFC)
Ethanol-soluble carbs (ESC)
Water-soluble carbs (WSC)
Starch
And better yet, for our purposes we can reduce it to just three: WSC, ESC and starch! So let’s concentrate on them.
Reading the assay: can we put it into plain English?
WSC (their dissolving in water has nothing to do with how they’re used in the body) reports both simple sugars and a more complex form of sugar called fructan. The reading tells us the total amount of those sugars as a percentage of the entire sample.
ESC (again, how they dissolve has nothing to do with how they’re used in the body) measures only carbs that dissolve in ethanol. Those are also simple sugars, along with just a trace  of fructan.
Starch reading shows just simple sugars.
That’s it, and you can see that all three are measures of simple sugars, while just one also contains a complex sugar.
The significance of the numbers
The sum of these three numbers – WSC, ESC and Starch -- gives us total sugar percentage in the hay sample, which is a figure of merit to guide us in determining if we want the hay in the first place. A total greater than 12% generally indicates too much sugar for sedentary horses, and for an IR horse, the preferred number is 10% maximum.
If the number for WSC is low, it means that there is relatively little fructan to reach the large intestine –good news for laminitic horses. (Why? Coming up.)
And if the numbers for ESC and starch are low, it means that simple sugars are low and will not evoke a strong glycemic response. That’s very good for IR horses (also coming up). In addition, since ESC and starch are also very low in fructan to begin with, there will be very little getting into the hind gut, very good for laminitic horses. Conclusion: low ESC and starch percentages are good news for both IR and laminitic horses.
Thus, in a nutshell, always look for hay with low WSC, especially if your horse is laminitic. If your horse is IR, look for hay with low numbers for all three – WSC, ESC and starch – and keep the total sugars below 12%.
The dangers of ignoring the numbers
But what if we don’t? What’s the downside? Let’s look at what happens. First, the large intestine and its friendly inhabitants are designed to handle fibrous matter, including complex sugars. They don’t handle simple sugars well at all – simple sugars are toxic to those microbes, and overloads of simple sugars – as well as complex sugars -- can result in massive die-offs of their population. One result of that carnage can be a colic attack. Another will be assimilation of those dead microbes into the blood stream. They are toxic to the horse, and seem to make a beeline for the laminae. Once there, they block those millions of microscopic blood vessels that feed the laminar cells, resulting in another massive cell die-off, this time in the hooves. That is laminitis.
A word of caution – excessive fructan can wreak as much havoc in the gut microbe population as an excess of simple sugars, and since the only measurement that includes fructan is WSC, it’s important that we not feed a hay with a high WSC reading – either or both simple sugars and fructan can be too high for the horse, with dangerous consequences.
Many of us unknowingly exacerbate the potential problem by something so simple as feeding our horse grain first, then follow it up with a batch of hay. If there must be grain in the horse’s feed, it needs to be digested and assimilated in the small intestine. Grain is high in simple sugars, and we’ve already seen what it can do in the large intestine. If enough grain goes in first, followed up by a load of hay, it gets pushed back, largely undigested, into the large intestine. Hay in the gut? Fine, that’s where we want it. Grain in the gut? Potentially serious colic or laminitis problems. Best to feed the hay first, grain last.
Pretty scary stuff, this. But we can mitigate the danger: while colic, insulin resistance and laminitis are dangers developing in part from an excess of sugars in the hay, with an assay report at your elbow, you can tell up front how safe your hay is for your horse.
What are the other carbohydrate-related entries on the assay?
For completeness’s sake, let’s define the other carb-related entries on the assay and whether or not they impact the amount of digestible carbohydrate in the sample:
Acid Detergent Fiber: a measure of the least digestible carbs. If you want to feed low-sugar hay, a relatively high ADF reading will be helpful.
Neutral Detergent Fiber: also a measure of un- or least-digestible carbs in the sample. Again, the higher the NDF percentage, the lower the percentage of digestible sugars.
Lignin: an indigestible component in plant cell walls that gives the plant rigidity and strength.
NFC: a rough mathematical estimate of non-fiber carbohydrate energy sources.
These contribute virtually no sugars to the diet, and in this context can be ignored.
Prevention of carbohydrate-related problems
Beyond attempting to clarify how to use the assay report, our focus, here, has been the impact of WSC, ESC and starch on IR and laminitic horses. But truth be told, it’s far, far better for your horse (and you) to PREVENT laminitis and IR in the first place. We can most assuredly use the assay report to help with that.
Since most domestic horses are not in heavy work and thus can’t work off sugar-provided energy very efficiently, we had best pay close attention to their diets in general. Many of us routinely feed grain to our horses, often because “it’s the way it’s always been done”. A strong argument can be made that many pasture-ornament horses, including those that get ridden lightly and only occasionally, can do quite well and quite safely on a forage-only diet – little or no grain at all -- as long as the minerals are balanced. Since grains in general are rich in sugars, feeding it every day along with high-sugar hay can easily cause the problems we’ve just described. A much better choice would be to choose your grain carefully, if you must feed it, then feed low-sugar hay plus selected supplements to ensure he gets good mineral balance. Take the time and trouble to get an assay of the hay you’re about to buy, and study WSC, ESC and Starch – use those numbers to gauge whether or not you really want that particular hay. Anyone who’s been there can tell you that they’d much rather have done a little homework first than suffer the agony – with their horses – of dealing with IR or laminitis later.
This report discussed only the matter of sugars in hay, and how to get useful information from the assay report. But you wouldn’t be reading this if you weren’t interested in feeding your horse properly, and so at this point, let me urge you to take it a step further and discuss your horse’s feed requirements with your vet or with an equine nutritionist. Everyone’s situation is unique, and some professional input makes it more likely that you’ll end up with the best diet for your horse. By all means, do ask every question that occurs to you – you’ll become your own “expert”, and your horse will be the lucky beneficiary.
How to buy good hay
An assay report is just a small sample test of a large batch of bales. We assume reasonable uniformity in the makeup of all the hay in that batch – could be a great many bales. But one assay report alone is useless if your hay comes from different sources each time you buy – you’d need an assay from each source. Ideally, you’ll find a hay source that you can buy as needed throughout the year, and the assay will be pertinent for all. You should talk to your “hay guy”, if he’s actually the “grower”, about the uniformity of his fields, and before you buy, ask permission to take a sample to submit for assay. Tell him you’ll give him a copy of the report – he may appreciate that very much, especially if it’s particularly good hay.

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