Rain affects relative feed value

Rain affects relative feed value Some hay samples from eastern South Dakota this year show a lower relative feed value (RFV) than producers were expecting.

South Dakota State University Extension Forage Specialist Peter Jeranyama explained that the issue is related to weather patterns.

"The major issue this year has been the good rains and at times excessive rainfall East River," Jeranyama said. "In a drought year carbohydrate sugars are concentrated in the plant and hence the quality test are higher than in a wet year. But in a wet year, the plant is actively growing � more fiber is produced and the high fiber content translates into low RFV."

Relative feed value is calculated by estimating the digestibility of the forage dry matter, and how much a cow can eat based on its "filling" capacity. However, Jeranyama added that cows sometimes perform differently even when fed forages of the same relative feed value � perhaps because of variations in the digestibility of the fiber fraction in the feed.

Jeranyama added that what is called the "relative forage quality" index, or RFQ, will provide a better measure of what feed is worth because it takes into consideration the differences in digestibility of the fiber fraction in the feed. That means the RFQ index can more accurately predict animal performance and match feed to animal needs.

When producers submit a hay sample for a forage quality analysis, the lab will give the relative feed value and relative forage quality indexes in its report to producers. The lab also will report total digestible nutrients (TDN).

Contact your local county Extension office for more about how to get a forage quality analysis done.

More about relative feed value and relative forage quality indexes is in an SDSU Extension Extra written by Jeranyama and SDSU Extension Dairy Specialist Alvaro Garcia.

SDSU Extension Extra 8149, "Understanding Relative Feed Value (RFV) and Relative Forage Quality (RFQ)," is available from county Extension offices. Or find it online at the SDSU Extension Web site, http://sdces.sdstate.edu/. Click on "Publications" near the top of the screen, then click the "Search" key at the right of the screen. Type "ExEx8149" into the "Item number" file field.

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