The term forage quality often is applied to the relationship between the nutritional characteristics of forages and the production of meat, milk, fiber such as wool or hair, or work. The term sometimes is considered synonymous with nutritive value (CSSA, 1992). In practice, however, forage quality frequently is reserved for the relationship between forage characteristics and animal daily response, while nutritive value is used to describe the relationship of plant chemical composition to nutrient digestibility and absorption (i.e., utilization) without necessarily taking into account factors related to intake and antiquality factors. Both of the latter must be considered, however, to extend the relationship to animal performance. This chapter addresses the anatomical and chemical constituents of tall fescue that relate to animal nutrition, narrowly defined as nutritive value. Other aspects of forage quality relating to intake and antiquality traits are addressed in sections dealing with animal responses (see Chapters 16 and Chapter 17). The in vitro bioassay for estimating apparent dry matter digestion will be referred to as dry matter disappearance (DMD) or in vitro true dry matter disappearance (TDD) and will be included with the nutritive value measurements.
The endophyte in tall fescue (Bacon and Siegel, 1988), Neotyphodium coenophialum, produces ergot alkaloids (see Chapters 13 and Chapter 14) that, when present in sufficient concentration in the forage, causes toxicosis in ruminants (Hill et al., 1994) and horses. These effects have complicated the interpretation of literature regarding the value of tall fescue as a livestock feed. Generally, the presence of toxins from the endophyte-grass symbiont is not reflected in estimates of the nutritive value determined on the forage (Bush and Burrus, 1988; Collins, 1991; Fritz and Collins, 1991; Turner et al., 1993), but can alter significantly the forage quality through negative influences on the physiology of the animal and, hence, on animal daily forage intake and rates of increase in body mass (see Chapter 12). The presence of toxins from the endophyte-host plant symbiont in tall fescue can depress animal growth and health substantially under a wide range of plant, animal, and climatic conditions (Stuedemann and Hoveland, 1988). Effects range from suppressed animal daily response in ruminants to aborted fetuses in horses and, in severe cases, loss of mature animals (see Chapter 18). The recent introduction of endophytes (see Chapter 20) that do not produce ergot alkaloids in tall fescue (Bouton et al., 2002) or modification of the endophyte presently found in tall fescue to reduce ergot alkaloid production (Hill et al., 2002) have shown potential to reduce or eliminate the impact of the toxicosis.
The development and release of modified or new cultivars (see Chapter 19) will require reevaluation and new documentation of the potential of tall fescue as a forage through a series of critical plant and animal evaluation trials. This chapter examines the nutritive value of tall fescue when grazed as pasture or clipped to simulate grazing, when accumulated as a stockpiled forage for late autumn and winter utilization, and when harvested and stored as hay or silage. A tabular format was selected for much of the data presentation to facilitate future additions as new data become available.
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