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United States Department of Agriculture

Agricultural Research Service

Title: Nonstructural Carbohydrates in Oat Forage

Authors
item Chatterton, N
item Watts, K - ROCKY MTN RESEARCH
item Jensen, Kevin
item Harrison, Philip
item Horton, William

Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 30, 2005
Publication Date: June 10, 2006
Citation: Chatterton, N.J., Watts, K.A., Jensen, K.B., Harrison, P.A., Horton, W.H. 2006. Nonstructural carbohydrates in oat forage. Journal of Nutrition 136:21115-21135.

Interpretive Summary: Nonstructural carbohydrates (NSC) in forage, such as glucose, fructose, sucrose, fructan and starch, may play a role in some horse diseases that involve carbohydrate intolerance, such as laminitis. Sugars in forage may adversely affect horses with dysfunctions of glucose metabolism. Insulin resistance has been associated with laminitis in horses. Cool-season grasses accumulate soluble sugars, starch, and fructan, while warm-season grasses accumulate soluble sugars and starch but no fructan. Thus, cool-season and warm-season grasses have different metabolic pathways by which they fix and store carbon. Nonstructural carbohydrates are the sum total of glucose, fructose, and sucrose (GFS), fructan, and starch. As a cool-season grass that utilizes fructan as a storage carbohydrate, oat forage is an appropriate model for investigating the relationships that influence fructan concentration. Because both environmental conditions and stage of plant maturity are thought to influence carbohydrate content of forages, an experiment was designed to quantify these influences in oats grown under field conditions and harvested for dry forage. The objectives of this study were to quantify NSC concentrations at various times during development in oats planted in both spring and summer, and to describe nutritional characteristics for both immature and mature plants grown in warm and cool environments. The amount of NSC present in harvested and grazed forages varied with several factors including date of planting, season of harvest, ambient temperatures, and plant maturity. Nonstructural carbohydrate contents should be considered when formulating feed for laminitic horses. The ideal approach is to chemically analyze all feeds. When feed analysis is not an option, practitioners should consider the following: 1) the concentrations of the various carbohydrate contents are not always inversely related to plant maturity. In fact, GFS (concentrations up to 15% dry weight), is the only carbohydrate fraction that always declines with plant maturity; 2) ambient temperatures at or just prior to harvest influence the amount of fructan in oat hay; 3) starch is present in vegetative tissues (up to 10% dry weight) and generally increases with maturity; 4) fructan and starch are the major NSC components in harvested oat hay, however, concentrations of GFS may be high during the joint and boot stages of growth; 5) ambient temperatures may be as important as plant maturity in determining NSC content of oat hay.

Technical Abstract: Nonstructural carbohydrates (NSC) fractions found in forage may play a role in equine diseases that involve carbohydrate intolerance, such as laminitis. Sugars in forage may adversely affect equines with dysfunctions of glucose metabolism. Insulin resistance has been associated with laminitis in equines. In this study, purified hydrolytic enzymes were used in the analytical procedures to separate starch, fructan, and sugars, thereby facilitating quantification of individual carbohydrate fractions. Cool-season grasses accumulate soluble sugars, starch, and fructan, while warm-season grasses accumulate soluble sugars and starch but no fructan. Thus, cool-season and warm-season grasses have different metabolic pathways by which they fix and store carbon. Nonstructural carbohydrates are the sum total of glucose, fructose, and sucrose (GFS), fructan, and starch. As a cool-season grass that utilizes fructan as a storage carbohydrate, oat forage is an appropriate model for investigating the relationships that influence fructan concentration. Because both environmental conditions and stage of plant maturity are thought to influence carbohydrate content of forages, an experiment was designed to quantify these influences in oats grown under field conditions and harvested for dry forage. The objectives of this study were to quantify NSC concentrations at various times during development in oats planted in both spring and summer, and to describe nutritional characteristics for both immature and mature plants grown in warm and cool environments. The oat cultivar 'Monida' was seeded on two planting dates in each of two years. Samples were air dried in mesh cages in the sun (to simulate drying conditions of farmer-harvested hay). Sugar concentrations in vegetative tissues were generally highest when plants were young and fiber was relatively low. GFS averaged about 15% dry weight in hay from oat plants in the boot stage at both planting dates and declined to 1 or 2% dry weight when mature. Conversely, starch, a storage carbohydrate, was present in low concentrations in young vegetative tissues (tiller to flowering stages) and then increased with plant maturity. In oat hay, starch increased from 3-4% dry weight early in plant development to 10-15% dry weight in mature plants. Fructan accumulations in oat hay, when considered across all planting dates, generally were not a function of plant maturity. In contrast, GFS and crude protein decreased with plant maturity while starch and neutral detergent fiber increased. Fructan concentrations were highest at the joint and boot stages of growth in April planted oats. In contrast, fructan concentrations were highest in plants at the milk or soft dough stages in the June planting. Nonstructural carbohydrate concentrations clearly demonstrated a disjunct relationship with plant maturity in oat hay. Oats planted early in the season had greater concentrations of NSC in immature than in mature oat hay. However, mature late-season planted oats had NSC concentrations similar to immature oat plants from the first planting. Following the joint stage, NSC concentrations decreased with advancing maturity in April planted oats. In contrast, NSC increased (2002) or changed only slightly (2003), depending on the year, in those planted in June.

Last Modified: 10/21/2014
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