Paper-Lecture29 - Characteristics of Plant Cell Walls...

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Characteristics of Plant Cell Walls Affecting Intake and Digestibility Forages by Ruminants’ H. G. Jung,*J and M. S. Allen? “ARS, USDA, Plant Science Research Unit and U.S. Dairy Forage Research Center Cluster, and University of Minnesota, St. Paul, MN 55108, tDepartment of Animal Science, Michigan State University, East Lansing, MI 48824 ABSTRACT: Even under the intensive concentrate feeding systems of ruminant animal production in United States, forages continue to represent the single most important feed resource. Cell-wall concentration and digestibility limit the intake potential and energy availability of forage crops in beef and dairy produc- tion. Identification of cell-wall characteristics that should be targets of genetic modification is required if plant breeders and molecular biologists are to success- fully improve forages for livestock feeding. As forage plant cell develops, phenolic acids andlignin are deposited in the maturing cell wall in specific structural conformations, and in a strict developmen- tal sequence. Lignin is the key element that limits cell-wall digestibility, but cross-linkage of lignin and wall polysaccharides by ferulic acid bridges may be a prerequisite for lignin to exert its affect. Lignin composition and p-coumaric acid in the wall are less likely to affect digestibility. Voluntary intake of forages is a critical determinant of animal perfor- mance and cell-wall concentration is negatively related to intake of ruminants consuming high-forage diets. Cell walls affect intake by contributing to ruminal fill. A simple model of cell-wall digestion and passage in which ruminal fill is a function of rates of digestion and passage, as well as the indigestible fraction of the cell-wall indicates that cell-wall concen- tration rate of passage are most critical parameters determining ruminal fill. Plant factors that affect rate of passageincludethose that affect particle size reduction by chewing and those that affect particle buoyancy intherumen.Thelatteris primarily affected by l) ability of the particulate matter to retain gases, which is probably related to plant anatomy of digestion of the tissue, and 2) at which the gas is produced, which is affected by the potentially digestible fraction of the matter of digestion of this fraction. Increasing of digestion should increase of passage by diminishing the produced and increasing density over time. A reduc- tion in the indigestible cell-wall fraction is beneficial because this will decrease fill and increase digestibil- ity. Animal production and economic benefits from reduced cell-wall concentration and increased digesti- bility are significant. Because of the high cell-wall concentration and large digestible cell-wall fraction of grasses, reduction in cell-wall concentration would probably be of greater value than improving digestibil- ity in these species. Legumes represent the opposite situation and may benefit more from improvements in the digestibility of their cell walls.
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This note was uploaded on 09/19/2011 for the course ANS 5446 taught by Professor Brown during the Spring '08 term at University of Florida.

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Paper-Lecture29 - Characteristics of Plant Cell Walls...

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