Forage tests today contain two values summarizing feed quality. While similar, understanding the unique differences of each is important to accurately value a forage. Today we will look at Relative Feed Value or RFV and Relative Forage Quality or RFQ.
For many years we have used a forage testing system that measured two different types of fiber called NDF and ADF. We used NDF to estimate how much hay cows would eat and we used ADF to estimate how much energy they would get from that hay. Then we combined those values to give an overall estimate of forage quality that we called RFV, which stands for relative feed value.
RFV did a fair job of estimating digestibility of legume hay, but its major flaw is assuming all fiber has the same digestibility. We know that is not true, and it especially misrepresents the forage quality of grasses. Grasses have more fiber than legumes but grass fiber usually is more digestible than legume fiber. For many years, there was no other forage test available at an affordable cost that was any better.
Eventually, low-cost tests were developed that did a good job of measuring digestible fiber. Forage scientists and animal nutritionists have worked together with these tests to also revise the intake and energy estimates so results from these tests predict how animals will truly perform much more accurately. With these new tests, a new overall estimate of forage quality was developed, which is called RFQ, or relative forage quality.
While this new RFQ test is especially useful when testing grassy hays, it also has been proven to be better with alfalfa and other legumes. So, when you test forages in the future, look for labs that offer relative forage quality. Your numbers will be more accurate.
By Jerry Volesky
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