Farmers and ranchers often tell University of Nebraska agronomist Bruce Anderson that their prairie hay, cane hay or other grass hay looks great but lab tests indicate a surprisingly low relative feed value (RFV). That's despite good protein and satisfactory total digestible nutrient (TDN) levels. So what's wrong with RFV?

Nothing is wrong, writes Bruce Anderson at, but it helps to understand how RFV is calculated and how it should be used.

First, RFV is calculated using only fiber values. Though protein certainly affects the value of hay, it has no effect on the calculation of RFV, he says.

RFV was initially developed for the dairy industry to help rank the potential energy intake of different hays by lactating dairy cows. And it does this quite well, especially for legumes like alfalfa.

Grass hay, however, is more difficult, as it has more fiber than alfalfa, which lowers its RFV. That fiber, however, often is more digestible than alfalfa fiber. Thus, grass hay frequently is ranked lower than it should be using RFV.

RFV also doesn't predict performance by other types of animals, such as beef cows, as well because potential energy intake doesn't have as much influence on their performance.

When you feed grass hay to animals other than dairy cows, focus on crude protein and TDN, Anderson says. RFV is much less important and could cause you to worry more than its worth.
-- Bruce Anderson, University of Nebraska-Lincoln