Tall Fescue Online Monograph

Abstract

The nutritive value of a forage largely determines ruminant animal daily performance through the provision of digestible energy, crude protein (CP), minerals, and vitamins. This chapter will examine the nutritional composition of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] in comparison with other perennial, cool-season grasses when managed as pasture, cut and preserved as hay or silage, or stockpiled in situ for later consumption. Unlike most cool-season grasses, the relationship between the nutritive value of tall fescue and animal daily response is variable. This is attributed to the presence of the endemic endophyte Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin, which causes the host plant-fungus symbiont to produce alkaloids that can influence negatively animal utilization of nutrients. The nutrient 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 perennial, cool-season 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 cool-season grasses is greater in spring growth, declines to a low in summer, and increases with the onset of autumn growth. Dry matter disappearance (DMD) has trends similar to those for CP, whereas fiber fractions increase in summer and decline in autumn. When stockpiling autumn growth for winter grazing, CP and DMD concentrations generally decline from early autumn to early winter, but increase again in late winter/early spring with the onset of new growth. Fiber fractions show an inverse relationship. Just as for most cool-season grasses, tall fescue CP and DMD concentrations increase and fiber fractions decrease with the supply of N fertilizer and with frequency of defoliation. Forage accumulated in summer for grazing during autumn and winter has greater CP concentrations when N application is deferred from June or July until September. When harvested and preserved as hay or silage, CP and DMD concentrations of tall fescue are similar to those of other cool-season grasses and all forages decline in both as plants mature from vegetative through the heading stage. The inconsistencies that exist between the nutritive value of tall fescue and animal daily responses are addressed, and consideration is given to the direction of future research.

Keywords: tall fescue, endophyte, Neotyphodium coenophialum, dry matter digestion, dry matter disappearance, crude protein, fiber, forage quality.

Abbreviations: ADF, acid detergent fiber; CP, crude protein; DM, dry matter; DMD, dry matter disappearance; NDF, neutral detergent fiber; TDD, true dry matter disappearance.