Validation of Brix for predicting sugar concentration and nutritive value of alfalfa and orchardgrass

Authors: Billman, Eric; Soder, Kathy; HORST, JEFF - Agri-King, Inc; HAFLA, AIMEE - Cargill Feed Applications; BALK, KRISTI - Agri-King, Inc

Submitted to: Crop, Forage & Turfgrass Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2024
Publication Date: 7/31/2024
Citation: Billman, E.D., Soder, K.J., Horst, J., Hafla, A., Balk, K. 2024. Validation of Brix for predicting sugar concentration and nutritive value of alfalfa and orchardgrass. Crop, Forage & Turfgrass Management. 40(4):437-445. https://doi.org/10.15232/aas.2024-02552.
DOI: https://doi.org/10.15232/aas.2024-02552

Interpretive Summary: Brix, a system using a refractometer that was developed to assess sugar concentrations of grapes and other fruits, has been anecdotally used by farmers to assess sugar concentration of fresh forages such as pasture. However, Brix values of forage species have never been validated with laboratory analysis via wet chemistry, posing a potential risk of farmers making incorrect management decisions when using Brix to assess nutrition of pastures for livestock. Results of this study found that using Brix as an indicator of forage quality, particularly sugar concentrations, shows some merit for forages legumes such as alfalfa that have greater soluble cell contents. However, forage grasses such as orchardgrass that contain less soluble cell contents may result in less reliable results, possibly due to fibrous particulate in the extracted fluid and other more reliable methods should be used.

Technical Abstract: Brix has anecdotally been touted as a potential tool for rapid and cost-effective assessment of forage sugar concentration and prediction of desirable forage nutritive values for ruminant livestock consumption. However, Brix has never been compared to wet chemistry values to verify these claims. This study sought to determine the validity of using Brix values of fresh forage to accurately predict desirable sugar and nutritive value concentrations. In 2019 and 2021, tissue samples from alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) monoculture pastures in central Pennsylvania, U.S. were collected monthly from May to September both years. Samples were immediately evaluated for Brix values with a hand-held digital refractometer, and the remaining biomass was frozen immediately with liquid N to halt cellular respiration. Samples were lyophilized and analyzed for individual sugars and wet chemistry nutritive values. Results showed that higher or lower Brix values did not equate to corresponding changes in wet chemistry forage nutritive values. Correlation analyses indicated that Brix was positively correlated (0.357 – 0.516) to individual and total sugars and net energy values in alfalfa, and negatively correlated (-0.439 – -0.519) to fiber, ash, and macrominerals (P, K, Ca, Mg). However, Brix values did not correlate to any notable nutritive value parameters in orchardgrass. Findings were attributed to greater fibrous fraction contamination, and the much lower sugar concentrations, found in grasses and legumes than in horticultural crops. Brix appears to be unreliable at consistently predicting high-sugar forages with desirable nutritive values.