Water- and ethanol-soluble carbohydrates of temperate grass pastures: a review of factors affecting concentration and composition

Authors: Kagan, Isabelle

Submitted to: Journal of Equine Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2022
Publication Date: 1/10/2022
Citation: Kagan, I. 2022. Water- and ethanol-soluble carbohydrates of temperate grass pastures: a review of factors affecting concentration and composition. Journal of Equine Veterinary Science. 110. Article 103866. https://doi.org/10.1016/j.jevs.2022.103866.
DOI: https://doi.org/10.1016/j.jevs.2022.103866

Interpretive Summary: Cool-season grasses contain water-soluble carbohydrates, which include small sugars such as sucrose, glucose, and fructose, and fructans, which are primarily chains of fructose that can vary in length. Ethanol-soluble carbohydrates consist of similar sugars, but their fructans are shorter. Large amounts of water- and ethanol-soluble carbohydrates have been correlated with high blood glucose or high insulin levels in horses. These put horses at risk for diseases such as laminitis, a painful hoof condition that is triggered by diet and often coincides with gastrointestinal disorders. A review was conducted of research from the past 11 years on conditions affecting amounts of water- or ethanol-soluble carbohydrates in grasses. The methods used to prepare samples and measure water- or ethanol-soluble carbohydrates probably affected the numbers obtained. Generally, water-soluble carbohydrates increased in cooler conditions. Water- and ethanol-soluble carbohydrates generally increased during the day, but not always. The grass variety used had variable effects on the amounts of carbohydrates measured. Usually, frequent cutting lowered the amounts of water-soluble carbohydrates present in tissue. The effects of fertilizing grasses with nitrogen varied, depending on the amount of fertilizer and the grass variety. Water stress had variable effects on water-soluble carbohydrates as well. Multiple factors need to be considered before assuming that water- or ethanol-soluble carbohydrates will increase or decrease under certain conditions.

Technical Abstract: Water-soluble carbohydrates (WSCs) of cool-season grasses include mono- and disaccharides and fructans (fructose-based polymers) of varying lengths. Ethanol-soluble carbohydrates (ESCs) consist of mono- and disaccharides and shorter fructans. WSCs and ESCs have been implicated in equine pasture-associated laminitis and other metabolic disorders. Peer-reviewed literature since 2010 was summarized for selected factors influencing concentrations and composition of WSCs and ESCs in cool-season grasses. The methods used to prepare samples and quantify WSCs or ESCs probably affected the concentrations measured. WSC concentrations tended to increase under cool temperatures and during cooler seasons. WSC and ESC concentrations generally increased from morning to evening with a range of -20 to 74 g/kg DM for WSCs. Cultivar choice had variable effects on WSC concentrations. Frequent defoliation usually lowered WSC and fructan concentrations. Nitrogen application increased or decreased WSC concentrations, depending on the amount applied and the genetic background of the grasses. Water stress had variable effects on WSC concentration and composition. Multiple factors should be considered before assuming how certain management or environmental conditions will affect WSCs, ESCs, or individual carbohydrates.