Relative Forage Quality (RFQ) vs.
Relative Feed Value (RFV)

 

Have you ever had two lots of alfalfa with the same relative feed value (RFV), one lot the cows milked great, ate it like candy and the other lot, the production dropped and the cows just didn’t seem to like the forage. We might have the answer to this problem.

For years, relative feed value (RFV) index has been widely used to determine the quality of a forage and therefore add some objectivity to determining a market value for a forage. It was developed primarily for alfalfa forages. The most accurate method to determine forage quality is to feed the forage directly to a group of animals and see how they perform. Since this generally is not feasible, we can only estimate potential animal performance. While RFV has been very valuable for marketing alfalfa hay, it has not been as useful or reliable as would be desirable in predicting livestock performance and or building rations, especially for grasses.

RFV is based on the concept of potential digestible dry matter intake of a forage by an animal. It is calculated from acid and neutral detergent fiber (ADF and NDF) concentrations in the forage. ADF concentration is used to estimate digestible dry matter (DDM) content, and NDF concentration is used to estimate potential dry matter intake (DMI) of the forage.

Measuring the actual digestibility of the fiber (NDF) component of forage provides a much better estimate of how the forage will perform in animal rations than does ADF. Fiber digestibility (NDFD) also affects potential intake. A new index called Relative Forage Quality (RFQ) has been developed by researchers at the University of Wisconsin as a replacement for RFV to provide a better index of how a forage will perform in an animal diet.

The two indexes are conceptually the same except that Total Digestible Nutrients (TDN) would replace DDM in the RFQ index calculation. TDN is estimated from the somewhat complicated calculation that includes an in vitro (in test tube) estimate of NDFD and crude protein, fatty acid, NDF and non-fibrous carbohydrate concentrations. DMI would be based on NDF, with an adjustment based on NDFD.

Several studies have been done on factors affecting digestible fiber. It’s been found that fiber is more digestible when grown under cooler conditions, therefore first cutting will tend to have more highly digestible fiber than later cuttings growing under higher temperatures. The same crop grown in northern states or Canada will tend to have more digestible fiber than when grown in states to the south. Alfalfa grown in higher mountain valleys of the West will have more digestible fiber than that grown in lower valleys. It’s also been found the fiber of leaves is both lower in content and higher in digestibility; therefore harvesting losses will result in greater RFQ loss than RFV. It’s also been determined that RFQ is reduced by heat damage but RFV is not.

Stearns DHIA Laboratories is now offering several NIR packages that include both RFV and the new RFQ indexes. Relative Forage Quality (RFQ) is only available at this time on Hay, Mixed Hay and Haylage. Corn Silage should be available very soon. This is a 48-hour in lab analysis.












Stearns DHIA Laboratories
825 12th Street South, PO Box 227
Sauk Centre, MN 56378-0227
320.352.2028 · 800.369.2697
Fax 320.352.6163 · Email

 

Hours
Monday-Friday: 8AM-4PM
Front Entrance Drop-Off Open 24 Hours
Refrigerator Available for Water, Milk,
and Wet Feed Samples