Location: Forage-animal Production ResearchTitle: Seasonal and diurnal changes in starch content and sugar profiles of bermudagrass in the Piedmont region of the United States Author
Submitted to: Journal of Equine Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2011
Publication Date: 9/1/2011
Citation: Kagan, I., Kirch, B.H., Thatcher, C.D., Teutsch, C., Elvinger, F.C., Shepherd, D.M., Pleasant, R.S. 2011. Seasonal and diurnal changes in starch content and sugar profiles of bermudagrass in the Piedmont region of the United States. Journal of Equine Veterinary Science. 31(9):521-529. Interpretive Summary: Pasture-associated laminitis causes severe lameness in ponies and horses. Laminitis has been correlated with consumption of large amounts of carbohydrates, particularly fructans, which consist of variable numbers of fructose units linked together. The solution would appear to be consumption of grasses that do not contain fructans, such as bermudagrass. However, laminitis can occur in horses grazing bermudagrass. The purpose of this study was to analyze the sugars in bermudagrass in order to have a better understanding of how these sugars may play a role in laminitis. Bermudagrass was collected from pastures for seven weeks, in the morning and the afternoon, to evaluate the amounts of sugars in the tissue at different times of the day throughout a growing season. Tissue was frozen immediately (to represent fresh pasture) or air-dried (to represent hay). Samples were analyzed for starch, ethanol-soluble carbohydrates (simple sugars), and water-soluble carbohydrates (simple sugars and fructans). In addition, specific sugars (glucose, fructose, and sucrose) were analyzed by chromatographic methods. Glucose and total simple sugars decreased during the collecting period, while starch increased. Dried tissue contained smaller amounts of glucose, fructose, and total simple sugars than did fresh tissue. Also, the amounts of these sugars varied less in dried than in fresh tissue. However, dried tissue contained more sucrose than fresh tissue. Sucrose, and total simple sugars, were more abundant in the afternoon than in the morning. Understanding these trends may help to make recommendations for grazing horses on bermudagrass in a way that reduces the risk of pasture-associated laminitis.
Technical Abstract: Seasonal and diurnal patterns of sugar accumulation in bermudagrass (Cynodon dactylon) pastures were monitored in order to evaluate risk factors for pasture-associated laminitis of ponies and horses. Bermudagrass was collected in the morning and afternoon on a weekly basis, from mid-July until late August. Tissue was air-dried to simulate hay, or frozen to retain the sugar profiles of fresh pasture. Samples were analyzed colorimetrically for total water-soluble and ethanol-soluble carbohydrates, and electrochemically for starch. In addition, sugars were separated and quantified by high-performance liquid chromatography coupled to pulsed amperometric detection (HPLC-PAD). The dominant sugars in extracts were glucose, fructose, and sucrose. Glucose and total ethanol-soluble carbohydrates decreased during the 7-week collecting period, while starch increased. Concentrations of glucose, fructose, and ethanol-soluble carbohydrates were lower and less variable in dried than in fresh tissue. Sucrose concentrations were higher in dried than in fresh tissue. Sucrose and total ethanol-soluble carbohydrates were more abundant in afternoon than in morning tissue. These results demonstrate trends in carbohydrate concentrations and profiles that may help to evaluate the likelihood of equine laminitis outbreaks on bermudagrass pastures and hay.