|LAWRENCE, LAURIE - University Of Kentucky|
|PRINCE, KELLY - University Of Kentucky|
|FOWLER, ASHLEY - University Of Kentucky|
|SMITH, S. RAY - University Of Kentucky|
Submitted to: Journal of Equine Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2017
Publication Date: 1/5/2018
Citation: Kagan, I., Lawrence, L.M., Seman, D.H., Prince, K.J., Fowler, A.J., Smith, S. 2018. Effects of sampling time, cultivar, and methodology on water- and ethanol-soluble carbohydrate profiles of three cool-season grasses in Central Kentucky. Journal of Equine Veterinary Science. 61:99-107.
Interpretive Summary: Cool-season grasses contain many different carbohydrates. Depending on the weather, time of day or year, and grass variety, the amounts and types of carbohydrates in grasses can be very different. Understanding how the amounts and types of carbohydrates change under different conditions can provide information on fluctuations in the nutrition of horses, thus helping with grazing management decisions for horses at risk for digestive disorders, such as laminitis. Three cool-season grasses common in Kentucky pastures (varieties of tall fescue, perennial ryegrass, and Kentucky bluegrass) were collected in the morning and afternoon on two different dates. The amounts and kinds of carbohydrates found in the three grasses depended on the laboratory techniques used to measure them, but also on the grasses and the time when they were collected. There were differences in the amounts and kinds of carbohydrates in tall fescue, perennial ryegrass, and Kentucky bluegrass. Therefore, to manage grazing for horses at risk for laminitis, the variety of grass in a pasture should be taken into account.
Technical Abstract: Cool-season grasses (CSG) accumulate variable amounts of water-soluble carbohydrates (WSC, mono- and disaccharides and fructans), depending on climate, time of day and year, and genotype. Fructan concentrations in CSG are sometimes estimated as the difference between concentrations of WSC and ethanol-soluble carbohydrates (ESC, mono- and disaccharides and small amounts of fructan). Characterizing both WSC and ESC components may improve understanding of soluble carbohydrate profiles in pastures and inform grazing management decisions, particularly for horses at risk for laminitis. Three CSG cultivars from Kentucky pastures were collected in the morning and afternoon on two springtime dates. WSC and ESC were extracted with water or 80% ethanol, respectively, and extracts were analyzed by high-performance liquid chromatography (HPLC) and a colorimetric assay. Method of analysis (HPLC or colorimetry), as well as extraction solvent (water or 80% ethanol), affected the composition of soluble carbohydrate determined in CSG samples, demonstrating the need to consider methodology when interpreting results. Total soluble carbohydrate concentrations were generally higher in the afternoon than in the morning, based on both HPLC (P = 0.0023) and colorimetric (P < 0.0001) analysis, and the diurnal variation was primarily due to sucrose (P < 0.0001). Mono- and disaccharides constituted the majority of the total soluble carbohydrate. The proportions of water- and ethanol-soluble fructan (P = 0.0101), and fructan chain lengths detected in water and ethanol extracts (P < 0.0001), differed among CSG cultivars. In choosing CSG for pastures, cultivar differences in both soluble carbohydrate composition and total soluble carbohydrate should be considered.