Seasonal and diurnal variation in water-soluble carbohydrate concentrations of repeatedly defoliated red and white clovers in central Kentucky

Authors: Kagan, Isabelle; ANDERSON, MEREDITH - University Of Kentucky; KRAMER, KELLY - University Of Kentucky; Seman, Dwight; LAWRENCE, LAURIE - University Of Kentucky; SMITH, S. RAY - University Of Kentucky

Submitted to: Journal of Equine Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2019
Publication Date: 11/29/2019
Citation: Kagan, I., Anderson, M.L., Kramer, K., Seman, D.H., Lawrence, L.M., Smith, S. 2019. Seasonal and diurnal variation in water-soluble carbohydrate concentrations of repeatedly defoliated red and white clovers in central Kentucky. Journal of Equine Veterinary Science. 84:102858. https://doi.org/10.1016/j.jevs.2019.102858.
DOI: https://doi.org/10.1016/j.jevs.2019.102858

Interpretive Summary: Grasses and clovers are important pasture plants. However, they contain a variety of carbohydrates (sugars, starch, and fiber), some of which may contribute to digestive disorders in horses grazing on pasture. Relatively little is known about how the water-soluble carbohydrate content of clovers--glucose, fructose, sucrose, and fructan (fructose chains), collectively referred to as sugars--is affected by time of day or season, especially for clovers common to central Kentucky, which has a large equine industry. In this study, two red and two white clover varieties, grown in plots consisting only of clover, were collected in the morning and afternoon from April to October, and sugar content was measured. Each harvest represented about four weeks’ growth. The most sugars overall were measured in May, July, August, and September. More sugars were present in the afternoon than in the morning in June, July, September, and October. Overall, red and white clover were not different in amounts of sugars, but in September and October, white clover contained more sugars than red clover. The amounts of sugars were similar to the amounts found in past studies of cool-season grasses. It is possible that if starch were measured as well, the amounts of carbohydrates in clovers would be high enough to be a concern for grazing horses. However, because grasses are sometimes lower in sugars if clovers are present, studies are needed on the water-soluble carbohydrate content of mixed grass-legume pastures in central Kentucky.

Technical Abstract: Water-soluble carbohydrates (WSC) of red (Trifolium pratense L.) and white clover (Trifolium repens L.) may contribute to the total WSC ingested by grazing horses. The goal of this study was to gain a better understanding of seasonal and diurnal variation in WSC of red and white clovers commonly grown in central Kentucky, and of their potential contributions to the WSC content of pastures. Two red and two white clover cultivars from monoculture plots were harvested after four weeks of growth from April to October of 2015, in the morning and afternoon of each harvest date. WSC were quantified by a colorimetric phenol-sulfuric acid assay. No main effect of species on WSC concentration was observed (P = 0.5198). However, an interaction (P < 0.0001) of species and harvest date was observed, with 20% more WSC in white than in red clover on two harvest dates. A main effect of time on WSC concentration was observed (P < 0.0001), with WSC 10% higher in the afternoon than in the morning. Species did not influence this diurnal variation (P = 0.2403). An interaction of harvest date and sampling time was observed (P < 0.0001), with WSC concentrations 10% higher in the morning in May, unvarying in April and August, and 20% to 30% higher in the afternoon in June, July, September, and October. The highest concentrations of WSC were about 100 mg/g. Further studies are needed to determine the relative contribution of clover to the nonstructural carbohydrate (WSC plus starch) content of mixed grass-legume pastures.