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

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?

—Via e-mail

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.

ADF and NDF in Horse Diets

When you’re reviewing a hay analysis note that NDF and ADF are predictors of plant maturity and, therefore, might indicate which horses that might do well on that particular hay. For example, hays with high NDF and ADF are not suitable choices for weanlings and lactating broodmares due to the high nutritional demands of growth and lactation and the lower nutritional value of more mature hays.

Guidelines exist for what are appropriate NDF and ADF contents for hay being fed to horses. Generally, NDF content of 40-50% and ADF content of 30-35% is considered ideal for performance horses, young stock, and broodmares. Mature horses at maintenance and easy keepers might benefit from hay with slightly higher values. Hays with an NDF more than 65% or an ADF more than 45% will have little nutritional value for horses but can be excellent choices for donkeys.

Take-Home Message

The NDF and ADF values on a hay analysis are two more pieces of information you can use to determine whether a hay is appropriate for your individual horse’s needs. When used in conjunction with other analysis results, they provide a more complete picture of a hay’s nutritional profile.

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