HAY & FORAGE GROWER – Have you ever been in a situation where you had great looking hay tested and were disappointed when the results came back with a low relative feed value (RFV)? According to University of Nebraska-Lincoln (UNL) Extension Forage Specialist Bruce Anderson, nothing may actually be wrong.
Relative feed value was originally developed with legumes such as alfalfa in mind for the dairy industry. Two types of fiber, acid detergent fiber (ADF) and neutral detergent fiber (NDF), are used to calculate RFV by estimating energy and intake, respectively.
This system uses the assumption that all fiber has the same digestibility. These days, we know this not to be true and, as a result, the forage quality of grasses is vastly misrepresented.
“Grasses have more fiber than legumes, but grass fiber usually is more digestible than legume fiber,” Anderson explains in UNL’s BeefWatch newsletter.
There is a more recent, low-cost test that is available to measure digestible fiber to better estimate the quality of grasses. This analysis is called relative forage quality (RFQ).
Along with this test, forage scientists and animal nutritionists have worked together to update intake and energy estimates to better predict animal performance.
The RFQ not only is useful with grass hays, it has also been proven to provide better estimates for alfalfa and other legumes.
“So when you test forages in the future, look for labs that offer RFQ; your number will be more accurate,” Anderson advises.
By Kassidy Buse, the 2018 Hay & Forage Grower summer editorial intern. She graduated from Iowa State University with a degree in animal science and is currently attending the University of Nebraska-Lincoln pursuing a master’s degree in ruminant nutrition.