Submitted to: Warm Season Grasses
Publication Type: Book / Chapter
Publication Acceptance Date: 2/26/2001
Publication Date: 1/20/2004
Citation: Coleman, S.W., Moore, J.E., Wilson, J.W. 2004. Quality and utilization. In: L.E. Moser et al. (ed). Warm Season Grasses. American Society of Agronomy, Madison, WI. Chapter 8, p.267-308. Interpretive Summary: The C4 grasses are important in supplying nutrients for both wild and domestic livestock in much of the world. Quality of Cr grasses is usually decreased in mid to late maturity, largely due to composition and structure of the cell wall portion of the plant. Cell wall concentration is large, and cell wall structure is variable; both are affected by species, maturity, fertility, and the environment, especially the temperature in which the forage plants are grown. The unique attributes of C4 grasses give strength to their adaptation, survival, persistence and productivity; however, the make evaluation of nutritive potential difficult. Both chemical composition and plant biology influence forage quality. The use of microscopic techniques to derive the ultrastructure of plant leaf and stem have been great aids to our understanding of how the plant is assembled through the growth process, and how it is dismantled through degradation by rumen microbes. Chemical composition determines, in part, the nutrient supplying ability of plants and the availability of the nutrients to ruminant animals that consume them. Furthermore chemistry and biology interact in both the assembly of the plant and in its degradation by chewing and the ruminal fermentation processes. The C4 grasses differ from C3 grasses in both chemistry and anatomy or structure. The C4 species differ from C3 grasses in both chemistry and autonomy or structure. The C4 species generally have more NFD and a smaller rate and extent of digestion; however at the same digestibility, intake of C4 grasses is greater than for C3 because at the same digestibility, C4 herbage would likely be less mature. During much of the year, C4 grasses do not supply all necessary nutrients in sufficient quantity for optimum animal performance Deficient nutrients may be supplied by supplements, but interactions of the base forage and supplements are likely to occur. These interactions often depress the expected outcome. Assessment of forage quality using animals is laborious, expensive, and time consuming. Hence, many methods have been tested to predict either forage quality (i.e., animal performance) or one of the components, forage intake, digestibility, and utilization. In spite of the efforts, there is a paucity of data available, collected in a systematic and consistent manner, from which to construct a suitable data base upon which to develop prediction equations.
Technical Abstract: Quality of warm season grasses, as indicated by their intake and digestibility, is normally lower than that of cool season grasses and legumes. This is a result of differences in chemistry (i.e., more cell walls and less cell solubles) and the ultrastructure of the plant tissue. Warm season grasses, however, are the staple diet of a majority of the domesticated ruminants in tropical and subtropical regions of the world. Quality may be affected by environmental conditions under which they are grown and management practices, such as fertilization and maturity at harvest. Their quality is generally under genetic control and most current breeding programs today include quality as one of the selection criteria. Since evaluation with animals is impossible in screening programs, many attempts at predicting forage quality, especially digestibility, have been made. In general, chemical composition is inadequate for prediction of forage quality over a range of forages. Bioassays, such as the in vitro system developed in the '70s, have had the greatest impact. New instrumen- tation, such as near infrared reflectance spectroscopy (NIRS) has much to offer for rapid, inexpensive (outside equipment costs) and nondestructive analysis. Unfortunately, instruments must be 'trained' with many samples (perhaps 100) with known values for forage quality. Research in the future should concentrate on developing databases with animal intake and in vivo digestibility under controlled conditions throughout the world. These databases could then be used as training data sets for NIRS. A salient feature is that databases of spectra may be collected on a single instru- ment and transferred to a 'standardized' instrument anywhere in the world.