Carbohydrates
Carbohydrates come in many forms some of 
which are structural and found in plant cell walls and others which are non-structural and found inside the cells. Structural carbohydrates help give the plant strength as it grows and are more complex in nature. As a result they cannot be digested by enzymes in the horse’s small intestine, and instead require microbial fermentation in the hindgut. Conversely non-structural carbohydrates (NSC) include starch and sugars that for the most part are broken down via enzymes and absorbed in the small intestine.
Non-structural carbohydrates
Starch and simple sugars enter the blood stream resulting in an increase in blood glucose and in turn insulin. For horses that are sensitive to readily available carbohydrates such as horses with polysaccharide storage myopathy (PSSM) or that suffer from an insensitivity to insulin (often referred to as insulin resistance), a history of laminitis, or have equine metabolic syndrome minimizing changes in blood glucose levels through the regulation of NSC intake is a vital component of successful management. Therefore knowing the NSC level of the forages you are feeding such horses is important.
Generally it is advised that these individuals should be consuming forages with an NSC of no more than 12% on a dry matter basis. When you look at the analysis results you receive from the lab you will often see two columns of numbers one labeled “as-is” or “as-fed” and the other labeled as “dry matter”. All feeds in the form that they are in when fed contain some level of moisture (represented by the as-fed values) and while this is what the horse is eating it makes comparison between feeds difficult so nutritionists compare feeds on a dry matter basis, without the water fraction.
Your forage analysis may not give you a value for NSC but if they provide you with values for percent starch and WSC (water soluble carbohydrates) you can calculate NSC by adding the two together. Water soluble carbohydrates are exactly as the name suggest, soluble in water. This means that if your hay provides more than 12% NSC and you are feeding a sensitive horse you can somewhat lower the level by soaking the hay in water before feeding it. Soaking for 30 minutes is generally enough to lower the WSC without leaching out other desirable nutrients however the amount of WSC removed varies. To be sure soaking has removed enough of the WSC fraction to make it safe to feed, a soaked sample should be tested by the lab.
You may also have heard of ether soluble carbohydrates (ESC). These are the simple sugars that along with starch enter the blood stream from the small intestine, they are a component of the WSC although do not comprise the entire WSC fraction. Because the ESC and starch fraction directly impact blood glucose levels some experts pay more attention to their levels in forage than the amount of WSC and starch recommending that the ESC plus starch should be 10% or less for sensitive horses.
The difference between the WSC and ESC fractions can be used as an estimate of the fructan content. Fructans are sugars but due to their complex structure they are not digested by enzymes in the small intestine instead going through microbial fermentation in the hindgut. This process is similar to the fermentation of the structural carbohydrates however fructans are very easy to ferment which can cause problems such as gas production and changes in the hindgut environment for some horses. While fructans in cool season pasture grass are of greatest concern in sensitive horses (especially those with a history of pasture laminitis), it is still advisable to choose hay with low NSC for these horses.
Structural Carbohydrates
Neutral and acid detergent fiber values are measures of structural carbohydrate and therefore their levels increase as the plant matures making them an indicator of the hays maturity at cutting. Neutral detergent fiber a measure of the plants cell wall content increases as the plant matures and is an indicator of how palatable the hay will be. As the plant matures the proportion of cellulose plus lignin (ADF) increase and the plant becomes less digestible. NDF levels below 40% are excellent and over 65% are unlikely to be eaten. ADF values over 45% have little nutritive value and below 31% are excellent. Horses working hard, broodmares and youngstock will benefit from hay with excellent NDF and ADF values and easy keepers will be able to consume more hay if it has slightly higher NDF and ADF content.
Other analysis
Much more information is also provided on the analysis sheet including the levels of numerous minerals, which can be very beneficial in helping to determine which feeds and supplements will compliment your hay and insure a balanced diet. Knowing what to do with this data can be confusing and working with a qualified equine nutrition professional is advised.
In conclusion
Forage is so much more than just bulk—it makes up the majority of your horse’s ration and is therefore a major source of nutrition it probably one of your biggest ticket purchases each year. While it can seem unreasonably expensive, making informed decisions and paying for good quality forage will save you money in other areas. Analyzing hay can help you make good purchase decisions and once purchased will help you make appropriate additional feed and supplement choices.
Get More from Your Hay Analysis Part III by Dr. Clair Thunes PhD is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.
Based on a work at http://summit-equine.com/hay-analysis-part-iii-carbohydrates
