Ozone Treatment of Forage: Structure and Digestibility of Different Types of Lignified Cell Walls
Ozone has been reported to reduce the lignin concentration in forages and to improve cell wall digestibility. The objective of this work was to evaluate the effect of ozonolysis on cell wall structure of various lignified tissue types in forages. In vitro digestibility was evaluated gravimetrically and by scanning electron microscopy for leaf blades and stems of ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] and for leaf blades of ‘Kentucky-31’ tall fescue (Festuca arundinacea Schreb.) and ‘Booneo’ orchardgrass (Dactylis glomerata L.). Ozonolysis of bermudagrass increased the in vitro digestibility by 12.5 percentage units over control material, and further showed that the epidermis, parenchyma bundle sheath, and lignified xylem cells of the vascular bundles in leaf blades were made more available for microbial degradation. Ozonated bermudagrass stems showed greater degradation of the parenchyma tissue, and cell wall widths of the more recalcitrant xylem and sclerenchyma ring were reduced in width. Ozone affected the most resistant tissues, i.e., xylem cell walls, and increased their susceptibility to microbial degradation at the surface of cut ends of sections. Ozonolysis of leaf and stem sections cut at 20-, 10-, and 5-mm lengths usually did not significantly (P > 0.05) increase in vitro digestibility of various lengths of leaves and stems of forages, indicating the inability to penetrate and improve tissue digestibility within intact sections. The ability of O3 to oxidize lignin without substantial losses of tissues may provide a means to elucidate the phenolic-carbohydrate interaction in cell walls.
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