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Horse Hay Analysis: What are ‘ADF’ and ‘NDF’?

Horse Hay Analysis: What are ‘ADF’ and ‘NDF’?
Acid detergent fiber and neutral detergent fiber measurements can help you decide if hay is good for your easier keeper, broodmare, or growing foal.
 
Q. I recently got my hay tested and received the analysis back. I have heard of water-soluble carbohydrates (WSC) and starch, but the analysis also lists “ADF” and “NDF” on it. What are they, and are they relevant?
 
A. The abbreviations “ADF” and “NDF” stand for “acid detergent fiber” and “neutral detergent fiber,” respectively. They are measures of feeds’ cell walls, or structural carbohydrate components.
 
Neutral detergent fiber is the insoluble carbohydrate fraction that remains after a sample of feed has been refluxed in a neutral detergent solution. It is made up of hemicellulose, cellulose, and lignin, all of which give the plant rigidity. The residue that remains after the NDF procedure has been completed is then refluxed in an acid solution; what remains after this process is cellulose and lignin, or ADF. These are not completely accurate procedures and the residues can be contaminated with carbohydrates such as pectins, which are not structural carbohydrates.
 
ADF, NDF, and Forage Quality
 
In ruminant nutrition NDF and ADF, along with crude protein, are used as measures of forage quality. This is because, as a plant ages, the amount of fiber increases and protein decreases as a percentage of dry matter. This also means that as a proportion of the dry matter, the amount of more readily available carbohydrates—such as starch and simple sugars—also tend to decrease.
 
Since the fibrous carbohydrate fractions require microbial fermentation in the hindgut, the energy contained within more mature plant material is considered less available. This might be beneficial if you’re feeding an easy keeper or a horse that needs hay with lower non-structural carbohydrates (NSC), because more mature hays with higher percentages typically yield fewer calories and contain less NSC.
 
In ruminant nutrition NDF content is used as a predictor of voluntary intake; cattle willingly consume less hay when the NDF content is particularly high. NDF might be a similar predictor in horses, although, due to anatomical differences between the equine and ruminant digestive tracts, it might not be as accurate of a predictor of intake in horses as in cattle.
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