| Abstrakt: |
Factors that influence rumen microbial degradation of switchgrass (Panicum virgatumL.) tissues are not well understood. Our objective was to measure and compare the anatomical degradation of leaf blades, leaf sheaths, and stems by tureen microorganisms. Two field‐grown switchgrass cultivars were harvested when three‐fourths of the inflorescence had emerged. Three‐millimeter portions of blade, sheath, and stem tissue were incubated in buffered rumen fluid for 0, 24, and 48 h, then removed and processed for light microscopy. Tissue composition and microbial degradation within each morphological component were measured with a computer‐based optical image analyzer. No differences in degradation were apparent between cultivars. The largest portion (35.7%) of blade cross‐sectional area was occupied by the mesophyll. After 48 h of incubation in rumen fluid, 32% of this tissue was partially degraded and 68% completely degraded. In contrast, leaf sheath parenchyma tissue was more resistant to complete degradation than that of the blade. In the sheath, 17.2% of tissues in the cross‐sectional area were at least 80% intact after 48 h of incubation; only 4.3% of the cross‐sectional area of the blade was this resistant to degradation. These differences in degradation resulted in lower (101 g kg−1) in vitro dry matter disappearance (IVDMD) in the sheath compared with the blade. Tissues (cortex, xylem, and bundle sheath) in which at least 80% of their area was intact after 48 h of incubation occupied 25.8% of the stem's cross‐sectional area. It is these resistant tissues that appear to cause the stem to have the lowest IVDMD of the three major morphological components of switchgrass. A detailed understanding of differences in degradation of anatomical tissues will result in the development of more digestible cultivars and morefficient forage utilization by livestock. |
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