Most Universities and equine nutritionists are encouraging horse owners to have their hay analyzed, especially if the quality of hay is a concern, or the horse is having nutritional problems. However, most horse owners need help interpreting the results of their analysis.
When your sample is returned, there will be two columns of numbers; As Sampled and Dry Matter. As sampled reports nutrient in their natural state, including water. Dry matter reports nutrients with the water (moisture) removed (water can have a diluting effect on the results). Either can be used for ration balancing, but be consistent. Below is a list of some (not all) common components analyzed for in hay.
Moisture - the optimum horse hay moisture ranges from 10 to 17%. Hay under 10% may be too dry, leading to brittle and dusty hay. Hays over 18% moisture have a high probability of molding (unless propionic acid is used), and hays over 25% moisture poses the threat of severe heat damage and serve as a potential fire hazard.
Crude Protein (CP) - a measure of the protein concentration of the hay. CP can range from 8 to 14% in grass hays (depending on nitrogen fertilization), 14 to 17% in mixed hays, and 15 to >20% in legume hays. Since most horses require approximately 10% crude protein, CP not likely to be limiting, except in lactating mares and foals.
Acid Detergent Fiber (ADF) - ADF is composed of cellulose, lignin, and other poorly digested components. The lower the ADF value, the more digestible the nutrients in the hay are. Vales of 30 to 35% are good and values above 45% maybe of little nutritional value.
Neutral Detergent Fiber (NDF) - NDF is a measurement of the insoluble fiber. In theory, the higher the NDF, the less a horse will consume. NDF levels between 40 and 50 are good, and those above 65 will likely not be consumed by most horses.
Relative Feed Value (RFV) - RFV is commonly used when selecting dairy quality hay. The utility of RFV in selection of horse hay is unknown, but can be used as a guideline. A RFV of 100 is considered the average. An equine nutritionist will not use RFV to balance a horse's ration.
Equine Digestible energy (DE) - Measure of the digestible energy in the hay, and used to balance the energy portion of the equine diet. For a light working horse, DE should be about 20 Mcal/day, and most hays range from 0.76 to 0.94 Mcal/lb of DE.
Equine Total Digestible Nutrients (Equine TDN) - This is a measure of the total digestible nutrients in the hay or its energy value, which may range from 40 to 55%. TDN is rarely used in evaluating horse hay.
Calcium (Ca) and Phosphorus (P) - These two macro-minerals are required in the diet by all horses in specific amounts, and vary among different types of hay. For the adult, maintenance horse, the CA:P ration should be between 3:1 to 1:1.
Once your hay has been analyzed, work with an equine nutritionists to balance your horse's ration. Generally speaking, a horse's ration is balanced in the following order: energy (fiber), protein, minerals, and vitamins.
By Martinson, PhD and Peterson, PhD, U of M
University of Minnesota Horse Newsletter (Volume 4, Issue 10, October 2008)