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Title: CAN TOTAL NONSTRUCTURAL CARBOHYDRATE – CRUDE PROTEIN BE USED TO PREDICT TOTAL DIGESTIBLE NUTRIENT – CRUDE PROTEIN RELATIONSHIPS OF COOL-TEMPERATE PASTURE HERBAGE?

Author
item Belesky, David
item Neel, James
item Ruckle, Joyce

Submitted to: American Forage and Grassland Council Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/23/2005
Publication Date: 6/11/2005
Citation: Belesky, D.P., Neel, J.P., Ruckle, J.M. 2005. Can total nonstructural carbohydrate – crude protein be used to predict total digestible nutrient – crude protein relationships of cool-temperate pasture herbage? In: Cassida, K. A. (editor). American Forage and Grassland Council Conference Proceedings, Bloomington, IL, 14:174-178.

Interpretive Summary: Estimating herbage nutritive value is difficult because of the complexity of plant composition, and the influence of environment, management, stage of development and genetic expression on that composition. The amount of herbage eaten depends on the concentration of available energy which is a product of structural and soluble carbohydrates in the plant. Laboratory procedures used to determine herbage composition and then estimate nutritive value to livestock are time-consuming and complex. A simple index of herbage energy relative to protein was constructed from soluble carbohydrate data and related to herbage energy computed from estimates of plant digestibility and chemical components. The data used to test the relationship and expand the model represented grazed stands composed of different forages including grasses, legumes and forbs. The soluble carbohydrate to protein quotient accurately predicts herbage energy relative to protein for cool-season grass and legume pastures. The index is not meant to replace detailed laboratory analysis but offers a simple and economical way to estimate herbage nutritive value.

Technical Abstract: Expressing energy relative to protein provides some understanding of nutrient balance and protein-use efficiency in the ruminant. Total nonstructural carbohydrates (TNC) are a readily fermentable energy source in the rumen, and when expressed relative to crude protein (CP) concentrations appear to be useful as a predictor of the relationship of total digestible nutrients TDN relative to CP. If the relationship holds for a range of forage species, management conditions and time, then TNC could serve as a rapid, cost-effective means to estimate herbage nutritive value for livestock grazing cool-temperate herbage. The TNC:CP relationship is not meant to replace the relatively more time consuming and labor intensive fiber and in vitro digestibility analyses where detailed nutritive value information is needed.