Good-quality hay is an important component of a horse’s diet, particularly in the winter when fresh pasture is not available.

One way to evaluate hay quality is to have your hay analyzed. Many different types of analyses are available, and the cost can range from $10-20 per sample to more than $100. The most extensive analysis will report more than 20 different nutrients or chemical fractions.

Although this detailed information makes sense to nutritionists, it is often not helpful to someone who wants to compare the values of different hays, or who wants an overall assessment of the hay’s nutritional value. To simplify the interpretation of hay analyses, nutritionists have come up with equations to give more general estimates of forage quality. One estimate of quality is relative feed value (RFV).

RFV was developed for cattle and takes into account the expected digestibility of the hay as well as the expected level of consumption. Basically, the assumption is the better the hay quality, the more easily the animal will digest it and the more it can consume. Digestibility and intake estimates are calculated from the concentration of neutral detergent fiber (NDF) and acid detergent fiber (ADF) in the hay. As a forage plant matures, it becomes more fibrous and stemmy, which results from increased NDF and ADF concentrations. So, as NDF and ADF increase, RFV decreases