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Sulfur Fertilization and Rumen Microbial Degradation of Cell Walls in Digitaria pentzii (Stent)¹

Sulfur fertilization of deficient Digitaria forages can increase voluntary intake and digestibility over unfertilized forages, and often the response is greater than that obtained with sulfur supplementation. Our objectives were to analyze D. pentzii grown with (+S) or without (–S) sulfur fertilization for anatomical changes related to digestibility and to determine the degradation of specific cell walls in each of these forages. Blades and stems were examined microscopically and percentages of tissue types in cross-sectional areas calculated. Cell wall digestion was evaluated by gravimetric analysis and by scanning and transmission electron microscopy. Our results indicated no differences in plant anatomy related to digestibility between the +S and –S forages. Digestibility studies using rumen microbial populations from sheep fed an alfalfa-oats (60:40) diet showed no differences dry matter digestibility or in the degradation of specific tissues. The degradation of the digestible leaf tissues, mesophyll and epidermis, was faster and more extensive with microbes from sheep fed +S D. pentzii than from those fed unfertilized forage. Further, sporangia-like structures that selectively attacked the sclerenchyma and the breakdown of sclerenchyma cells in association with pleomorphic microbial structures occurred within animals fed +S but not –S forage. The parenchyma bundle sheath, cuticle, and lignified vascular tissue were not degraded with any of the microbial inocula or with pure cultures of Ruminococcus flavefaciens FD-I. Results indicated that sulfur-fertilization did not affect plant anatomy but enhanced the fiber-digesting capability of the rumen population. Additional research is necessary to delineate microbial differences and their relationship to fiber degradatio

Key Words: Forage quality • Plant anatomy • Electron microscopy • Light microscopy

² Microbiologist, USDA and animal nutritionist, CSIRO (Present address: Division of Tropical Animal Production, Davies Laboratory, Townsville, Qld., Australia.), respectively.

Received for publication November 29, 1982.