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Publication Date
1981
Description
Cell walls of forage were studied for structural and chemical factors that limit digestion by rumen microorganisms. Techniques used to investigate digestion were histochemistry, electron microscopy, and anaerobic culturing of rumen populations on specific substrates. Certain tissues, such as the xylem cells, totally resisted degradation by rumen microorganisms; these tissues stained positive for lignin with acid phloroglucinol (Weisner test). Other supportive tissues, such as the sclerenchyma in blades, stained positive for lignin with chlorine-sulfite (and also the Maule test) and were also generally resistant to microbial digestion. Microscopic studies revealed that certain living tissues (i.e., those having cytoplasm and organelles indicative of metabolic activity) were only slowly or partially degraded in particular forage grasses, notably warm-season species. Coastal bermudagrass and Boone orchardgrass, low- and high-digestibility grasses, respectively, were compared for the manner of attack by rumen microorganisms on digestible cell walls, using electronc microscopy. Tissues encompassing about 70 % of the cross-sectional area and including the mesophyll, phloem, parenchyma bundle sheath, and inner part of the epidermis in orchardgrass leaf blades were degraded, often without the necessity of bacterial adherence, whereas only about 30 % of the tissues (i.e., mesophyll and phloem) in bermudagrass blades were degraded in this manner. Although the percentages of the various types of adhering bacteria were similar in these forage species, more total bacteria associated with orchardgrass cell walls. Anaerobic culturing on media containing xylan, pectin, or cellobiose of bacterial populations adapted to orchardgrass or bermudagrass fiber resulted in larger total bacterial counts for orchardgrass-adapted populations; numbers of xylan-using bacteria were significantly (P..; 0.05) higher. Further, the hemicellulolytic protozoan Epidinium €caudatum form caudatum degraded the mesophyll, parenchyma sheath, and epidermis of orchardgrass but did not attack tissues of bermudagrass. The data derived from electron-microscopic and anaerobic-culturing studies indicated that carbohydrates in bermudagrass fiber were less available to rumen microbial digestion than those in orchardgrass fiber. Histochemical studies with the chlorinesulfite test indicated that certain living tissues (i.e., parenchyma bundle sheath) that were only slowly or partially degraded in bermudagrass were lignified, which could explain the lack of availability of the carbohydrates within the cell walls to rumen microorganisms. These data indicated that the carbohydrates, especially the hemicelluloses, in the digestible cell walls vary in their inherent availability to rumen microbial enzymes. Possibly, chlorine-sulfite lignin plays a significant role in limiting the rate of digestion of living tissue types in particular forages.
Citation
Akin, D E., "Structural Characteristics Limiting Digestion of Forage Fiber" (1981). IGC Proceedings (1977-2023). 9.
(URL: https://uknowledge.uky.edu/igc/1981/section8/9)
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Archival
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Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Structural Characteristics Limiting Digestion of Forage Fiber
Cell walls of forage were studied for structural and chemical factors that limit digestion by rumen microorganisms. Techniques used to investigate digestion were histochemistry, electron microscopy, and anaerobic culturing of rumen populations on specific substrates. Certain tissues, such as the xylem cells, totally resisted degradation by rumen microorganisms; these tissues stained positive for lignin with acid phloroglucinol (Weisner test). Other supportive tissues, such as the sclerenchyma in blades, stained positive for lignin with chlorine-sulfite (and also the Maule test) and were also generally resistant to microbial digestion. Microscopic studies revealed that certain living tissues (i.e., those having cytoplasm and organelles indicative of metabolic activity) were only slowly or partially degraded in particular forage grasses, notably warm-season species. Coastal bermudagrass and Boone orchardgrass, low- and high-digestibility grasses, respectively, were compared for the manner of attack by rumen microorganisms on digestible cell walls, using electronc microscopy. Tissues encompassing about 70 % of the cross-sectional area and including the mesophyll, phloem, parenchyma bundle sheath, and inner part of the epidermis in orchardgrass leaf blades were degraded, often without the necessity of bacterial adherence, whereas only about 30 % of the tissues (i.e., mesophyll and phloem) in bermudagrass blades were degraded in this manner. Although the percentages of the various types of adhering bacteria were similar in these forage species, more total bacteria associated with orchardgrass cell walls. Anaerobic culturing on media containing xylan, pectin, or cellobiose of bacterial populations adapted to orchardgrass or bermudagrass fiber resulted in larger total bacterial counts for orchardgrass-adapted populations; numbers of xylan-using bacteria were significantly (P..; 0.05) higher. Further, the hemicellulolytic protozoan Epidinium €caudatum form caudatum degraded the mesophyll, parenchyma sheath, and epidermis of orchardgrass but did not attack tissues of bermudagrass. The data derived from electron-microscopic and anaerobic-culturing studies indicated that carbohydrates in bermudagrass fiber were less available to rumen microbial digestion than those in orchardgrass fiber. Histochemical studies with the chlorinesulfite test indicated that certain living tissues (i.e., parenchyma bundle sheath) that were only slowly or partially degraded in bermudagrass were lignified, which could explain the lack of availability of the carbohydrates within the cell walls to rumen microorganisms. These data indicated that the carbohydrates, especially the hemicelluloses, in the digestible cell walls vary in their inherent availability to rumen microbial enzymes. Possibly, chlorine-sulfite lignin plays a significant role in limiting the rate of digestion of living tissue types in particular forages.
