Suppose you will pasture dairy or beef cows in an intensive grazing system. You want to move them to the right paddocks at just the right times to maximize efficiency based on forage quality. Some livestock producers use the Brix test to determine sugar content in forage. In theory, that allows them to graze animals on the highest-quality forage every day. Should you use it, too?

Based on science, Kathy Soder and colleagues at the USDA Agricultural Research Service Pasture Systems and Watershed Management Research Unit, located in State College, Pa., suspected the Brix test may not be as reliable a predictor of sugar content in forages as some believe.

To test their suspicions, the researchers collected forage samples monthly from May through August on an alfalfa field and an orchardgrass field in central Pennsylvania. After plant tissue was crushed in a garlic press, they took readings with a refractometer, performing the Brix test. Uncrushed samples were later tested for sugar content.

Brix results inconsistent

“The Brix test was a fair predictor of forage sugars in alfalfa in May and June and in late summer,” Soder says. “However, it was not a good predictor in July.

“For orchardgrass, the Brix method was a very poor predictor of sugars at all times. Frequently, either it predicted the opposite of measured sugar content, or there was no correlation.”

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The Brix method simply measures refracted light, Soder notes. It is adept at measuring dissolved solids in liquids and is used routinely to measure sugar content in wine, honey and fruit. The sugar content is high in those items compared to forages. Plus, liquids extracted from forages contain other things besides sugars, including oils, minerals, pectins and proteins.

If it is a solid dissolved in a liquid, Brix will measure it, Soder emphasizes. “Other factors including humidity levels, dew on leaves and even human error also impact Brix results,” she adds.

Other ways to measure forage quality

“Our results confirm that Bix refractometers may not be accurate enough to quantify sugars in forages,” Soder says. “There are just too many variables, which can result in inconsistencies.

“Farmers may want to consider more accurate methods of assessing energy content of forages in decision-making. A farmer may decide they’re not comfortable depending on Brix measurements as an indicator of forage quality.”

Sending forage samples to a lab for analysis using traditional wet chemistry is one option but isn’t practical for making daily decisions on pasture quality. However, testing with a hand-held near-infrared device, using NIR technology, might be an option, Soder notes.

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Researchers Jerry Cherney and Debbie Cherney at Cornell University and Matthew Digman at the University of Wisconsin have evaluated several hand-held NIR units. In the journal Sensors, published in August, along with co-author William Yamada, also at UW, they presented results after testing units on 600 undried samples of mixed haylage, pulled from 111 bunker silos on New York farms.

“Comparative analyses, particularly for undried forage, have aligned with the findings from the literature, confirming the validity of our models within the expected performance parameters,” the authors state.

Where is forage quality testing headed? “The evaluation of embedded NIR sensors in agricultural machinery to predict forage quality and properties is one of the paths forward in undried forage research,” the authors conclude.