Understanding Hay (Forage) Analysis

By Wendy Mollat, DVM, DAVCIM(LA)

Laboratory hay analysis is a useful tool for assessing the quality and composition of your horses’ hay so that you can choose an appropriate supplement to ensure your horses are receiving a well-balanced diet. There are several key factors in acquiring a good sample so that you have reliable results. It is just as important to be able to decipher all the information that the laboratory returns to you.

Sampling

Many large-scale hay distributors will provide analysis of their hay upon request. If the batch you buy has not already been tested, you can still have the test done yourself so that you and your veterinarian can work together to adjust your horses’ diet accordingly. Depending upon the test chosen, price for hay analysis can range widely. Generally, the most basic test will be acceptable for most horses, unless you are working specifically with a nutritionist to more finely balance your horses’ diet.

Proper sampling using a hay probe is critical to getting a reliable result. Simply grabbing a handful from several bales of hay will not yield a representative sample. To obtain a representative sample of the hay lot you will need a combined sample from 15-20 bales of hay. All major laboratories recommend obtaining the sample using a manual or mechanical core hay sampling device. Most laboratories that provide hay testing services will have a visual guide on their website describing how to properly acquire a representative sample.

Interpreting Results

Moisture content (Dry Matter) – Feed (grain) labels are usually reported on an “as fed” basis. Hay analysis reports will generally contain two columns; one “as fed” and one “dry matter.” When assessing nutrient values to balance a horse’s ration either set of values will work. However, when comparing one hay to another or comparing hay to pasture analysis, the “dry matter” values should be used to remove the variation in water content from the picture. Good quality hay will have a moisture content of about 10%. Hay with a moisture content above 13% is more susceptible to mold and is not generally considered of good quality for horses.

Crude Protein – This is an estimate of the amount of protein in the hay, but it does not reflect the quality of the protein in the hay. Many factors affect the availability of the protein to your horse. Protein levels will vary with stage of maturity and type of hay. In general, grass hays will have lower protein (7-14%) than alfalfa hay (15-22%). Hay with less than 10% crude protein may not meet the protein requirements for your horse unless their diet is supplemented with an additional protein source.
Fiber and Relative Feed Value – These are important values in determining the digestibility of the hay. Neutral Detergent Fiber (NDF) reflects total fiber content in the hay. Hay with high NDF (>60%) is less palatable and is less digestible than hay with an ideal NDF value of 35-55%.

Acid Detergent Fiber (ADF) is a measure of cellulose and lignin in hay. The higher the ADF, the lower the hay’s digestibility and energy content. Prime hay has an ADF value of 25-35%.
Relative Feed Value (RVF) is an estimate of the plant maturity at harvest and is determined by comparing the ADF and NDF of a sample. The higher the RVF, the higher the hay quality. Hay with RVF of 74 or less is considered unfit for horses due to poor digestibility. The RVF of prime hay approaches 151.

Carbohydrates – With increasing awareness of equine metabolic issues, carbohydrate content in feed has received increased scrutiny. Hay analysis reports will generally include several values representing the hay’s carbohydrate content:

  • non-fiber carbohydrate,
  • ethanol soluble carbohydrate (ESC),
  • water soluble carbohydrate (WSC), and
  • starch.

Non-structural carbohydrates (NSC) are a general measure of sugar, starch and fructan concentration in hay. NSC can be calculated by adding WSC and starch. While opinions vary on which value is most useful when evaluating feed for a horse with an underlying metabolic disorder, you are generally safe primarily using NSC to determine whether the hay is appropriate. The NSC value of hay is naturally within the tolerance range of normal horses; however, horses that require a diet limited in starch and sugar should be fed hay with an NSC no more than 10-12%.

Minerals and Vitamins – The minerals reported on a hay analysis are essential nutrients for horses. For some minerals, such as calcium and phosphorous, it is important to have an overall ratio of 2 parts calcium to 1 part phosphorous. Imbalances can lead to metabolic bone disorders like “big head.”
In the Northwest, the soil is deficient in selenium; consequently, the hay that is grown here is deficient in selenium. At Pilchuck Veterinary Hospital we see several cases each year of selenium deficiency. These horses are generally on only hay with no other vitamin and mineral supplement.

Equine nutrition is a huge field and can be a daunting subject. If you have concerns about your horse’s diet, we are here to help!