|HARRISON, PHIL - Retired ARS Employee|
|CHATTERTON, N. - Retired ARS Employee|
|CREECH, J. - Utah State University|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2014
Publication Date: 9/1/2014
Citation: Jensen, K.B., P. Harrison, N.J. Chatterton, B.S. Bushman, J.E. Creech. 2014. Seasonal trends in nonstructural carbohydrates in cool- and warm- season grasses. Crop Science. 54:1-13.
Interpretive Summary: Temperate cool-season forage grasses make a major contribution to the profitability of agriculture. In an attempt to increase forage intake by animals, grass breeders have developed cultivars with an increased ability to accumulate high concentrations of carbohydrates, which are generally considered advantageous, however, there are times during the growing season when increased carbohydrate levels, particularly fructan, has been associated with the increased incidence of equine laminitis. This study evaluates the effect of harvest date (May to November) on 13 cool- and two warm-season grass species in northern Utah as it relates to sugars (glucose, fructose, and sucrose), fructan, water-soluble carbohydrates (WSC), starch, and total nonstructural carbohydrate levels (TNC). Under the conditions of this study, considerable variation exists in the cool-season grasses for sugar, fructan, WSC, starch, and TNC concentrations to select for target nutritional levels based on livestock needs. For instance, of the high yielding irrigated pasture grasses such as meadow bromegrass had numerically lower overall sugar, fructan, WSC, starch, and TNC concentrations across harvest dates than the other grasses examined thus, it would be a species to consider if low sugar concentrations where the target for sugar sensitive grazing animals. Based only on TNC values, if a high TNC animal diet is desirable, then perennial ryegrass and timothy would be the species of choice. On pastures that are considered dryland or having limited irrigation, if with low contents of readily available carbohydrates is the desired feed, Sandberg bluegrass and tall wheatgrass would be species to consider.
Technical Abstract: Grass breeders have historically selected for and developed cultivar with an increased ability to accumulate high concentrations of nonstructural carbohydrates (NSC). While increases in NSC content of forages are generally considered advantageous, there are times during the growing season when increased NSC level, particularly fructan, has been associated with the increased incidence of equine laminitis. Hence, there is a need to better understand trends in sugars (glucose, fructose, and sucrose), fructan, water-soluble carbohydrates (WSC), starch, and total nonstructural carbohydrates (TNC) throughout the growing season as stockpiled forage. This study evaluated 13 cool- and two warm-season grass species once a month from May to November in northern Utah during 2004 and 2005 for sugars, fructan, WSC, starch, and TNC. Warm-season grasses had uniformly lower sugar, fructan, WSC, and TNC concentrations than cool-season grasses; however, they had dry matter yields (DMY) higher than cool-season grasses in August. Throughout the growing season if a high TNC diet is desired, then, of the grasses examined, perennial ryegrass and timothy would be the species of choice for irrigated pastures. However, if less TNC were desired then meadow bromegrass, which had the lower overall sugar, fructan, WSC, starch, and TNC concentrations, would be best. On pastures that are considered dryland or having limited irrigation, Sandberg bluegrass and tall wheatgrass had the lowest overall forage nutritional quality, while crested wheatgrass had excellent forage nutritional quality at maturity. Under the conditions of this study, there appears to be sufficient variation in the cool-season grasses for sugars, fructans, WSC, starch, and TNC concentration to select for targeted nutritional levels for an array of livestock needs.