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Relationship of Tissue Digestion to Textural Strength in Bermudagrass and Alfalfa Stems

Richard B. Russell Agric. Res. Ctr., USDA-ARS, P.O. Box 5677, Athens, GA 30613

^* Corresponding author.

Forage quality is determined to a large extent by the physical degradation of fiber and by exit of the digesta from the rumen. The effect of plant structure and prior microbial activity on the ease of physical breakdown, which occurs during chewing, is poorly defined. The objectives of this work were to identify structural characteristics primarily responsible for providing textural strength in stems and to relate this strength to tissue digestion by whole rumen fluid, by bacteria, or by fungi. The textural strength of stem residues was determined by applying force perpendicularly to the longitudinal axis of l-cm stem sections. Three-millimeters stem sections from the fourth and fifth internode of ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] stems and from midway of stems of ‘120’ alfalfa (Medicago sativa L.) plants were incubated with the microbial groups or in control media for 72 h and compared for percentage area of tissue lost in cross sections or for the cross-sectional width of tissues remaining in stems. Rumen fluid and bacteria degraded substantial amounts of the stem parenchyma, but rumen fungi degraded significantly (P 0.05) lower amounts. None of the microbial groups removed the lignified ring tissues in either forage, and loss of other tissues within plants was similar for the microbial groups. Stems incubated with fungi were reduced the most in textural strength. Results indicated that the presence and integrity of the lignified ring was the primary structure responsible for strength in stem residues and that removal of parenchyma from stems under the conditions of this study was not a major factor affecting textural strength of stem residues.

Received for publication November 20, 1989.

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