Ethanol-soluble carbohydrates of cool-season grasses: prediction of concentration by near-infrared reflectance spectroscopy (NIRS) and evaluation of effects of cultivar and management

Authors: KRAMER, KELLY - University Of Kentucky; Kagan, Isabelle; LAWRENCE, LAURIE - University Of Kentucky; SMITH, S. - University Of Kentucky

Submitted to: Journal of Equine Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2021
Publication Date: 2/19/2021
Citation: Kramer, K.J., Kagan, I., Lawrence, L.M., Smith, S.R. 2021. Ethanol-soluble carbohydrates of cool-season grasses: prediction of concentration by near-infrared reflectance spectroscopy (NIRS) and evaluation of effects of cultivar and management. Journal of Equine Veterinary Science. 101. Article 103421. https://doi.org/10.1016/j.jevs.2021.103421.
DOI: https://doi.org/10.1016/j.jevs.2021.103421

Interpretive Summary: Cool-season grasses, which comprise the majority of grasses in central Kentucky pastures, contain both structural carbohydrates, like cellulose (fiber), and nonstructural carbohydrates. The latter include simple sugars like glucose, fructose, and sucrose, as well as fructans (fructose chains of varying lengths). For measurement, the simple sugars and short fructans can be dissolved in ethanol and are referred to as ethanol-soluble carbohydrates (ESC). High amounts of ESC may exacerbate the risk of pasture-associated laminitis, a disease that can affect horses and ponies grazing on pasture. ESC can be measured in the laboratory with wet chemistry, but the laboratory methodology can be time-consuming and costly for a large number of samples. One goal of this study was to measure ESC of a sample subset with wet chemistry and use that information to predict ESC of other similar samples by near-infrared reflectance spectroscopy (NIRS). A second goal was to use the predicted ESC values to assess the effects of cultivar (variety) and management on concentrations of ESC in ten cool-season grass cultivars across four species collected in the morning and afternoon on ten harvest dates. The NIRS prediction had greater than 95% accuracy, based on comparisons of the predicted ESC concentrations with corresponding laboratory-determined concentrations. ESC concentrations increased in the afternoon compared to the morning. Applying nitrogen fertilizer to plots did not affect ESC concentrations in the majority of samples. Use of NIRS has the potential to evaluate management and cultivar effects on ESC concentrations in cool-season grass pastures.

Technical Abstract: Ethanol-soluble carbohydrates (ESCs) of cool-season grasses include mono- and disaccharides and sometimes short-chain fructans, which may exacerbate the risk of pasture-associated laminitis. A calibration for prediction of ESC concentrations by near-infrared reflectance spectroscopy (NIRS) was developed from 323 samples of four cool-season grass species (orchardgrass, Kentucky bluegrass, tall fescue, and perennial ryegrass) across 10 cultivars collected in central Kentucky in the morning and afternoon over two growing seasons. The calibration, which had accuracy above 95%, was used to predict ESC concentrations of 1532 samples from the second growing season. ESC concentrations increased in the afternoon compared to the morning across all cultivars. In the majority of samples, ESC concentrations were not affected by nitrogen application to plots. Use of NIRS has the potential to evaluate management and cultivar effects on ESC concentrations in cool-season grass pastures.