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item Burns, Joseph

Submitted to: Tall Fescue Information System
Publication Type: Review Article
Publication Acceptance Date: 7/10/2004
Publication Date: 11/13/2004
Citation: Burns, J.C. 2004. Nutritive value. Tall Fescue Information System.

Interpretive Summary: This is one chapter (Chapter 9) of 19, that addresses tall fescue ranging from its origin, through its nutritive value and animal utilization to its future use in animal production systems. This chapter addresses the nutritive value of tall fescue including estimates primarily of in vitro dry matter disappearance, crude protein, neutral detergent fiber and its constituent fiber fraction of acid detergent fiber, cellulose, hemicellulose, and lignin. Consideration is give to the nutritive value of tall fescue when used for pasture, when harvested and stored as hay or silage or when accumulated in late summer for fall and winter grazing. In the latter case total nonstructural carbohydrates are also addressed. In general, the nutritive value of tall fescue was not altered greatly by the presence of an endemic toxic endophyte nor was there major differences among cultivars. Tall fescue had similar nutritive value to other coal-season grasses such as orchardgrass, bromegrass or reed canarygrass when managed similarly. Crude protein concentrations were increased by nitrogen application and nutritive value declined with increasing physiological maturity. This is consistent with other cool-season grasses. This chapter address the paradox of tall fescue being of similar or greater nutritive value compared with other cool-season grasses but frequently resulting in suppressed (variable) animal daily responses. The replacement of the endemic- toxic endophyte with either an endemic or inserted nontoxic endophyte provides the tall fescue plant with added persistence but does not produce the alkaloides associated with animal toxicosis. Such improved tall fescue cultivars now becoming available may broaden the use of tall fescue in animal production systems.

Technical Abstract: The nutritive value of a forage is associated with subsequent animal daily performance. Generally, forages with greater concentration of cell solubles, including Crude Protein (CP), will have reduced concentration of cell walls and will be positively associated with animal daily performance. The objective of this chapter is to examine the chemical composition of tall fescue with comparison to other C3, perennial, coolseason grasses when managed as a pasture, cut and preserved as hay or silage, or accumulated in the summer as a stockpile for subsequent winter grazing. Unlike most coolseason grasses, the relationship between the nutritive value of tall fescue and animal daily response is variable. This is attributed to the presence of an endemic endophyte which produces alkaloids and can negatively influence animal responses. The chemical composition of tall fescue, however, is not altered by the presence of the endophyte. In general, the nutritive value of tall fescue is similar to that of other C3, perennial, coolseason grasses when managed similarly. Under grazing conditions the CP concentration, the most comprehensive index of nutritive value in the literature, of tall fescue and other coolseason grasses is greater in spring growth, declines to a low in the summer (July) and increases with the onset of fall (October) growth. Tall fescue is responsive to nitrogen fertilization, as are other coolseason grasses, with CP concentration increasing to over 300 g kg-1 when topdressed with > 500 kg N ha-1. Further, CP concentrations are greatest for most coolseason grasses maintained under frequent vs infrequent defoliation regimes. When harvested and preserved as hay or silage CP concentrations of tall fescue are similar to other coolseason grasses and all forages showed reduced CP concentration as plants matured from vegetative through to the heading stage. Forage accumulated in the summer for grazing during the fall and winter had greater CP concentrations when N application was deferred from June or July until September. Frequently, CP concentrations of tall fescue were somewhat less (10 to 30 g kg-1) compared with other coolseason grasses when accumulated and sampled in early fall. Clipping tall fescue and other coolseason grasses in the fall, compared with stockpiles, maintained greater CP concentrations, regardless of accumulation dates. When utilizing stockpiled tall fescue or other coolseason grasses in December or January, CP concentrations were reduced compared with October, but increased in February or March with the onset of new growth. Consideration is given to estimates of dry matter disappearance, fiber fractions and soluble carbohydrates. The paradox that exists between the nutritive value of tall fescue and animal daily responses is addressed and consideration is given to the direction of future research.