RFV or RFQ: Does it make a difference?
We often hear conversations about relative feed value (RFV) and relative feed quality (RFQ), but not in the context of the specific merits of certain forages used in a dairy ration. That’s because those two acronyms mean more when you compare the relative dollar value of different forages in the market. Sure, nutritionists will sometimes talk about RFV and RFQ as it relates to how a certain forage is feeding, but we have better parameters today to plug into modern dairy ration programs to evaluate feeding characteristics in far greater detail.
If you’re standing at a hay auction and preparing to bid on a certain lot of hay, it’s much easier to have a single number that describes the relative feeding characteristics of that hay than mentally calculate how much to pay based on a detailed feed analysis.
RFV is the “old timer” of the two measures and has been around for more than 25 years. In its simplest form, Kansas State University researchers describe it as a measure to predict how well a forage will be consumed and digested. Dr. Dan Undersander, University of Wisconsin-Madison forage agronomist, describes RFV as a measure based on digestible dry matter intake (DMI) relative to a standard forage. In other words:
DMI is estimated from neutral detergent fiber (NDF), while digestible DM is estimated based on acid detergent fiber (ADF). The 1.29 constant was chosen based on animal performance data, and so full-bloom alfalfa would come out with an RFV of 100. As good as this early estimation was, the fallacy was that it assumes ADF has a constant relationship to digestibility, which is not necessarily the case, according to Undersander.
Enter the new measure of feed quality, RFQ, in 2002. According to Undersander, the new NRC requirements, at the time, recognized RFV’s shortcomings for dairy cattle and added a total digestible nutrients (TDN) component instead of the digestible DM factor. The new formula is:
The 1.23 constant was used to keep the result in the same realm of numbers as the old RFV formula because hay buyers and sellers were used to that.
According to a 2007 study, when you compare the two formulas for alfalfa, they have a similar range with little variation. However, Cumberland Valley Analytical Services has data that shows more variation and outliers when grasses and mixed forages are analyzed for RFV and RFQ. Under no circumstances should RFV and RFQ be used for corn silage because these equations don’t consider starch digestibility.
UW-Extension suggests hay is worth about $1.25 to $1.50 per ton per point above the base price of 100 RFQ feed. Let’s say you’re standing at a hay auction and have your eye on some 150 RFQ hay. Common 100 RFQ hay is going for $80 per ton. This formula would indicate that you can afford to pay $67.50 to $75 per ton over the 100 RFQ feed price, or about $147.50 to $155 per ton.
This article was originally written for the May 2018 edition of Vita Plus Forage Foundations. Click here for more forage management expertise.
About the author: Jon Urness is a retired Vita Plus national forage specialist. He grew up on his family’s five-generation homestead dairy near Black Earth, Wis. and still lives there today. He graduated from the University of Wisconsin-Madison in 1977 with a bachelor’s degree in agricultural journalism. As Vita Plus employee owner, Urness provided on-farm dairy nutrition consulting in southwest Wisconsin, as well as forage marketing responsibilities outside of the traditional Vita Plus market.
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Feed quality and nutrition