For release: May 9, 2003
Contact: Alvaro Garcia, (605) 688-5488

Relative Feed Quality and Relative Feed Value

 BROOKINGS, S.D. -- Relative feed quality, or RFQ, is a good means of assessing feed value for those who buy and sell forages, a South Dakota State University specialist said.

SDSU Extension Dairy Specialist Alvaro Garcia said although the industry has evaluated feeds based on "relative feed value," relative feed quality may better reflect the performance that can be expected from cattle.

Relative feed value (RFV) has been used for years to compare the quality of legume and legume/grass hays and silages, Garcia noted. Having one index to price hay and predict animal performance has been very useful for livestock producers and hay farmers.

But one concern has been the difference in performance observed in animals fed forages with similar RFV values. Relative feed value is calculated by estimating the digestibility of the forage dry matter, and how much the cow can eat based on its “filling” capacity. However, cows sometimes perform differently even when fed forages of identical RFV.

One of the concerns is the accuracy of the estimation of fiber digestibility, Garcia said. Fiber from grass and legumes naturally differ in digestibility, as it also does when grown under different ambient temperatures. First-cutting alfalfa harvested at a similar stage of maturity to second and third cuttings will have identical RFV. Therefore, differences in fiber digestibility are not taken into account and cows may perform differently.

"Researchers at the University of Wisconsin suggested an alternative to overcome this problem," Garcia said. "The relative feed quality (RFQ) index uses fiber digestibility to estimate intake as well as the total digestible nutrients (energy) of that forage. The RFQ is thus an improvement over RFV for those that buy and sell forages, as it better reflects the performance that can be expected from cattle."

One other advantage of the RFQ prediction is that it differentiates legumes from grasses. The higher neutral detergent fiber in grasses will make RFQ a better predictor of quality than RFV.

Forage labs that are part of the Midwest NIRS consortium, such as SDSU's Olson Biochemistry Laboratories, have equipment calibrated to measure the digestibility of this fiber fraction.

A forum May 14 at the Midwest Dairy Institute near Milbank will address this and other topics to improve forage quality and animal performance. The Midwest Dairy Industry and SDSU Cooperative Extension are sponsoring the seminar. To register call the Midwest Dairy Institute at (605) 432-9000.
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Lance Nixon, Editor
AgBio Communications Unit
South Dakota State University
ACC, Box 2231, Rm 200
Brookings SD 57007
Telephone: (605) 688-4653
LANCE_NIXON@SDSTATE.EDU