Using a Brix Refractometer to Test Hay, Grass and Forage for Livestock

Hay, pasture grass and other forage crops are among the most important components of livestock feeding programs. Cattle, horses, sheep, goats and other grazing animals depend on forage for much of their daily nutrition, yet two bales of hay that look almost identical can have very different nutritional characteristics.

Color, smell, leafiness, maturity and texture can provide useful clues, but visual inspection cannot tell a producer how much water-soluble material is present in the plant. Laboratory forage analysis remains the most comprehensive way to determine nutritional characteristics such as crude protein, fiber, energy and water-soluble carbohydrates. However, laboratory testing takes time and requires sending a sample away.

A refractometer provides a fast way to take a measurement directly from plant sap or a prepared forage extract.

For producers who want a quick field measurement, a Brix refractometer can provide useful information about the soluble material present in grass and forage. The technique is particularly interesting for fresh pasture grasses, legumes and other forage plants where sap can be extracted directly from the plant.

For dried hay, the process is different. Hay does not contain enough free liquid to simply squeeze out several drops of juice. Instead, a standardized water-extraction procedure can be used to produce a liquid sample that can be measured with a refractometer.

The key is consistency.

What Does Brix Measure in Forage?

Brix is traditionally associated with sugar concentration in products such as fruit juice, grapes, honey and other agricultural products. In a refractometer, Brix is derived from the refractive index of the liquid placed on the instrument's prism.

Forage is more complicated.

The liquid extracted from a grass or legume contains more than sugar. Water-soluble carbohydrates can include sugars and fructans, along with minerals, organic acids, amino acids and other soluble compounds. Consequently, a Brix reading should not automatically be interpreted as an exact percentage of sugar in the forage.

Mississippi State University Extension specifically cautions that forage Brix is not an exact measurement of sugar because numerous soluble compounds contribute to the reading. Environmental conditions, plant species, maturity, time of day, soil moisture, fertilization and other factors can also influence Brix measurements.

That does not make a refractometer useless. Quite the opposite.

A properly standardized Brix measurement can provide a rapid, inexpensive way to monitor changes within a forage crop or compare samples collected under similar conditions.

Why Would a Livestock Producer Test Grass or Hay?

Forage can change considerably during the growing season.

The soluble carbohydrate concentration of grass can vary with plant species, weather, sunlight, maturity, fertilization and the time of day the sample is collected. Research on cool-season grasses has demonstrated differences in water-soluble carbohydrate concentrations based on species, cultivar, management and sampling time.

That creates several potential uses for a Brix refractometer.

A rancher could measure fresh pasture at different times of day. A farmer could compare forage before and after a change in fertilization or irrigation. A hay producer could establish a consistent sampling and extraction procedure and monitor different hay lots.

The measurement is particularly valuable when it is used as a screening or comparison tool rather than as a stand-alone nutritional analysis.

For example, if the same field is measured every week using the same sampling procedure, a producer can establish a history of Brix readings. Changes in those readings can provide additional information about the forage.

Fresh Grass Is the Simplest Forage to Test

Fresh forage provides the easiest sample for a refractometer because plant cells contain sap that can be mechanically extracted.

The basic procedure is straightforward.

Collect a representative sample of grass or legume from several locations. Avoid unusual plants, dirt and contaminated material. Cut the sample into manageable pieces and place a small amount into a clean garlic press or similar plant press.

A garlic press is not simply a convenient kitchen tool for this application. Extension guidance specifically identifies a garlic press or another type of press as a way to extract plant sap for forage Brix testing.

Squeeze the sample and collect several drops of the resulting juice.

Place a drop on the refractometer prism, close the daylight plate and take the reading.

For the most repeatable results, take multiple readings rather than relying on one measurement. Clean the prism between measurements and use the same sample preparation procedure each time.

Why an Automatic Temperature Compensation Refractometer Helps

Temperature affects refractive-index measurements.

This is one reason an ATC, or Automatic Temperature Compensation, refractometer is useful for field work. The BOSS 0–18% Brix ATC Refractometer is designed with automatic temperature compensation, making it practical for measurements in changing field conditions. The instrument has a 0–18% Brix range, 0.20% Brix divisions and stated accuracy of ±0.15% Brix.

The ATC feature does not correct for differences in sampling or extraction. It simply addresses temperature-related changes in the optical measurement.

That distinction matters.

A highly repeatable sample-preparation procedure is just as important as the refractometer itself.

What About Dried Hay?

Testing baled hay requires a different technique.

Once forage has been dried, much of the plant's water is gone. A garlic press will not normally produce enough liquid from dry hay to make a useful refractometer measurement.

The solution is to create a standardized hay-water extract.

A measured quantity of hay is combined with a measured quantity of distilled or deionized water. The sample is then allowed to extract for a predetermined amount of time with controlled agitation. The liquid is separated from the plant material and placed on the refractometer.

This produces a measurable liquid extract.

The resulting Brix number should be identified as the Brix of the hay extract, rather than claiming that it represents the exact sugar percentage of the original hay.

That distinction is critical.

Water-soluble carbohydrate extraction is already an established laboratory approach for studying forage. Research has shown that water extraction can remove substantial amounts of soluble carbohydrate from hay, and the amount recovered depends on conditions such as temperature, agitation and soaking time.

Therefore, anyone using a refractometer to compare dried hay should keep the extraction procedure identical from sample to sample.

A Recommended Hay Extraction Procedure

For field screening, a practical starting procedure is:

1. Obtain a representative sample

Take hay from multiple portions of a bale or from multiple bales within the same lot. Mix the material to create a representative composite sample.

Do not base the measurement on a single handful pulled from one location.

2. Reduce the hay to a consistent size

Cut or grind the hay into relatively uniform pieces.

A laboratory forage grinder provides the greatest consistency, but a clean forage cutter can be adequate for a field screening procedure.

3. Weigh the sample

Use a small digital scale and record the exact mass.

For example, a testing procedure could begin with 10.0 grams of prepared hay.

4. Add a fixed amount of water

Add a predetermined volume of distilled or deionized water.

A 1:10 hay-to-water ratio, such as 10 grams of hay with 100 mL of water, is a reasonable starting point for developing a standardized procedure. It should be considered a proposed testing protocol rather than an established industry standard.

5. Agitate for a fixed period

Mix the sample for the same amount of time every time.

The purpose is to make the extraction reproducible.

6. Separate the liquid

This is where filtration becomes important.

The Best Way to Filter Hay Extract

A coffee filter is inexpensive and readily available, but it would not be my first choice for a standardized BOSS hay-testing procedure.

Coffee filters vary in construction, filtration characteristics and flow rate. They are designed for brewing coffee, not for producing standardized analytical samples.

A better approach is two-stage filtration.

First stage: coarse pre-filtration

Pass the hay extract through a clean, fine nylon mesh or laboratory sample strainer.

The purpose is simply to remove large pieces of grass and hay fibers.

A reusable laboratory-grade nylon mesh filter is preferable because it can be washed and used consistently. A disposable fine-mesh tea strainer or similar food-grade mesh could be useful for early field experiments, but a defined mesh size would be better for a commercial procedure.

Second stage: laboratory filter paper

After removing the larger fibers, pass the liquid through qualitative laboratory filter paper.

A small funnel and laboratory filter paper provide a much more controlled filtration step than a coffee filter.

The objective is not to remove dissolved sugars. It is to remove suspended plant particles that could interfere with the optical measurement.

This produces a much clearer sample for the refractometer prism.

An even better option for development work

If you are developing the procedure before selling it as a kit, compare filtered samples with centrifuged samples.

Centrifugation can separate fine suspended plant particles without relying on a disposable paper filter. A small laboratory centrifuge would obviously be less convenient for a rancher, but it can help determine whether suspended solids are affecting the refractometer reading during method development.

Once the effect is understood, the simpler filtration method can be selected for field use.

Measuring the Hay Extract

Once the extract is clear:

1. Allow the sample to reach a consistent temperature.

2. Confirm the refractometer calibration.

3. Place a few drops on the prism using a clean pipette.

4. Close the daylight plate.

5. Take the reading.

6. Clean and dry the prism.

7. Repeat the measurement.

Three measurements from the same prepared extract provide considerably more information than a single reading.

Record the average and the individual readings.

For example:

Reading 1: 6.2°Bx
Reading 2: 6.3°Bx
Reading 3: 6.2°Bx
Average: 6.23°Bx

That is much more useful than simply writing down "6° Brix."

If the three readings are widely separated, the problem should be investigated rather than averaged away. Suspended particles, poor sample coverage, contamination, temperature differences or inconsistent extraction can all contribute to variability.

Why the BOSS 0–18% Brix Refractometer Is a Good Fit

The BOSS 0–18% Brix Refractometer is particularly interesting for forage screening because its measurement range is concentrated in the lower Brix range rather than extending unnecessarily into the very high concentrations encountered in products such as jams, syrups and fruit concentrates.

The BOSS model features a 0–18% Brix scale, 0.20% divisions, automatic temperature compensation and a stated accuracy of ±0.15% Brix. It is a mechanical optical instrument that requires no battery and includes a pipette, calibration screwdriver, hard case and user guide.

For field forage work, that combination has some practical advantages.

There is no battery to recharge, the instrument is portable, and the ATC feature helps accommodate changing field temperatures.

It is also worth emphasizing that the BOSS instrument is a general-purpose Brix refractometer. It has not been specifically validated as a laboratory hay-sugar analyzer. The accuracy specification refers to the instrument's Brix measurement, not to the ability of Brix to predict the complete nutritional value of hay.

That distinction should remain clear in any livestock application.

What Brix Can and Cannot Tell You About Hay

Brix can provide a rapid measurement of dissolved material in a forage extract.

It can potentially be useful for:

• Comparing forage samples.

• Monitoring changes in fresh pasture.

• Establishing a field-specific Brix history.

• Screening forage before sending samples for laboratory analysis.

• Investigating differences between grass species or harvest conditions.

• Providing an immediate field measurement when laboratory results are not available.

But Brix does not replace a complete forage analysis.

Laboratory testing remains the appropriate method when a producer needs dependable information about crude protein, NDF, ADF, digestible nutrients, energy, minerals or water-soluble carbohydrates.

Research specifically examining Brix as a predictor of forage sugar has produced cautionary results. A USDA Agricultural Research Service study comparing Brix measurements with laboratory analyses found that Brix did not reliably predict sugar concentration or commonly used forage-quality measures in alfalfa and orchardgrass.

A later 2024 peer-reviewed study likewise examined whether Brix could predict sugar concentrations in fresh alfalfa and orchardgrass.

This is why the most responsible use of a forage Brix refractometer is as a rapid screening and comparison instrument, not as a replacement for laboratory nutrition testing.

Brix Testing Is Particularly Interesting for Pasture Management

Fresh pasture may be an especially useful application.

Grass is a living plant, and its water-soluble carbohydrate concentration can change throughout the day and with environmental conditions. Research on cool-season grasses has documented differences associated with time of day and other environmental and management factors.

A producer could therefore establish a consistent sampling routine:

Morning: collect and measure forage.

Afternoon: collect and measure forage.

Following week: repeat the process.

Over time, the producer builds a Brix history for that particular pasture.

That is potentially more meaningful than comparing one isolated Brix reading with a generalized chart.

What About Horses, Cattle, Sheep and Goats?

The same basic principle applies across livestock species: forage quality matters, but nutritional requirements differ among animals.

Horses have received considerable attention in research involving water-soluble carbohydrates because some horses require careful management of carbohydrate intake. Research has shown that soaking hay can reduce water-soluble carbohydrate content, with the amount removed depending on soaking conditions.

Cattle, sheep and goats also consume large quantities of forage, but their nutritional requirements and digestive systems differ.

For that reason, a Brix reading should never be treated as a universal "safe" or "unsafe" number for every animal.

The value of the refractometer is the measurement itself and the ability to compare samples using a consistent procedure.

Building a More Useful Forage Testing System

The real opportunity is not simply putting a refractometer on a table next to a bale of hay.

It is creating a repeatable forage sampling system.

A useful field kit could contain:

• BOSS 0–18% Brix ATC Refractometer

• Sample container

• Small digital gram scale

• Stainless or nylon sample strainer

• Laboratory-grade filter paper

• Small funnel

• Disposable transfer pipettes

• Distilled or deionized water

• Sample bags

• Cleaning supplies

• Written extraction instructions

For fresh forage, the producer could use a clean garlic press or plant press to obtain sap.

For dried hay, the producer could use the measured water-extraction procedure.

The same amount of forage, same water volume, same extraction time, same filtration method and same measurement procedure should be used every time.

That is how a simple Brix reading becomes a useful monitoring tool.

The Bottom Line

A refractometer cannot tell a livestock producer everything about a bale of hay.

It can, however, provide something that laboratory testing cannot provide as conveniently: an immediate measurement in the field.

For fresh grasses and legumes, sap can be extracted with a garlic press or plant press and measured directly.

For dried hay, a controlled water extraction is more appropriate. The extract should be passed through a coarse mesh to remove larger fibers and then through laboratory-grade filter paper to produce a clearer liquid sample. Coffee filters can work for experimentation, but standardized laboratory filter paper is a better choice for a repeatable procedure.

The BOSS 0–18% Brix ATC Refractometer provides a practical instrument for this type of low-range Brix screening. Its 0–18% scale, 0.20% divisions, automatic temperature compensation and portable design make it well suited to field measurements of liquid forage extracts.

Most importantly, Brix should be treated as a screening measurement and monitoring tool, not as a substitute for laboratory forage analysis.

When used consistently, a refractometer can give livestock producers another piece of information about their pasture, grass and hay and can help identify samples that deserve closer laboratory examination.

BOSS 0–18% Brix Refractometer for Forage and Hay Testing

The BOSS 0–18% ATC Brix Refractometer is available from National Industrial Supply for applications requiring rapid measurement of dissolved solids in liquid samples.

Specifications:

• 0–18% Brix range

• 0.20% Brix divisions

• ±0.15% stated accuracy

• Automatic Temperature Compensation (ATC)

• Heavy-duty aluminum construction

• No batteries required

• Hard protective case

• Calibration screwdriver

• Transfer pipette

• User guide

For forage testing, the instrument can be used to measure fresh plant sap or a properly prepared liquid extract from dried hay and other grasses.

Important: Brix readings from forage should not be interpreted as an exact percentage of sugar or as a complete measurement of nutritional quality. Laboratory forage analysis remains the appropriate method for detailed nutritional evaluation.

National Industrial Supply

National Industrial Supply
30777 Rancho California #891420
Temecula, CA 92589, USA

Sales: 951.308.9269
Email: nisupply@gmail.com
Website: www.nisupply.com

National Industrial Supply specializes in refractometers and related measurement equipment for industrial, agricultural, food, beverage and specialty applications.

For questions about selecting a refractometer for a specific application, contact NI Supply and describe the material you need to measure, the expected concentration range and how the sample will be collected.