Location: Forage-animal Production ResearchTitle: Seasonal and diurnal variation in simple sugar and fructan composition of orchardgrass pasture and hay in the Piedmont region of the United States Author
Submitted to: Journal of Equine Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2011
Publication Date: 5/30/2011
Citation: Kagan, I., Kirch, B.H., Thatcher, C., Strickland, J.R., Teutsch, C.D., Elvinger, F.C., Pleasant, R.S. 2011. Seasonal and diurnal variation in simple sugar and fructan composition of orchardgrass pasture and hay in the Piedmont region of the United States. Journal of Equine Veterinary Science. 31:488-497. Interpretive Summary: Seasonal and diurnal changes in nonstructural carbohydrate profiles were studied in orchardgrass pastures in the Piedmont region of Virginia. Grass was sampled weekly in the morning and evening from 4 experimental plots over an 8-week period (early to late spring). Tissue was air-dried to simulate hay, or frozen on dry ice. Samples were extracted by boiling and separated by high-performance liquid chromatography coupled to pulsed amperometric detection. Fructan, glucose, fructose, and sucrose were quantified. Fructan content was highest in the early spring in both frozen and dried tissue. Glucose and fructose content were significantly higher in fresh than in dried tissue on most sampling dates, while the reverse was true of sucrose. These results may explain trends in sucrose accumulation observed in earlier studies and indicate that the simple sugar composition of orchardgrass differs greatly between hay and pasture.
Technical Abstract: Laminitis, a disease that causes lameness in horses, is thought to result from grazing on grass high in carbohydrates. Consequently, knowing the amounts and types of carbohydrates in a pasture may help horse owners to manage grazing in a way that reduces the risk of laminitis. This study describes the analysis of carbohydrates in orchardgrass collected near the Southern Piedmont Agricultural Research and Extension Center (Blackstone, VA). Orchardgrass samples were collected one day a week, in both morning and evening, for 8 weeks (April-June). In this way, diurnal as well as seasonal changes in carbohydrates could be followed. Upon collection, part of the sample was frozen on dry ice, and part was air-dried to simulate hay production. Carbohydrates were extracted by boiling samples in water and separated by high-performance liquid chromatography (HPLC) with electrochemical detection. In both frozen and air-dried tissue, fructans (fructose chains of varying lengths), were most abundant in the early spring. Also, on the earliest collecting date, fructans were significantly higher in the evening than in the morning. Glucose and fructose content did not differ significantly in morning and evening samples, but these sugars were significantly higher in frozen than in air-dried tissue. Sucrose, while barely detectable in fresh tissue, was the dominant simple sugar in air-dried tissue, and generally more abundant in evening than in morning samples. These results indicate that in orchardgrass, the simple sugar composition of hay differs greatly from that of pasture. Also, season and time of day can affect the types and amounts of carbohydrates taken in during grazing.