Ruminal Digestion of Ammonium Hydroxide-Treated Wheat Straw Observed by Scanning Electron Microscopy1

Abstract

Ammonium hydroxide-treated and untreated wheat straw stems were compared for differences in digestive patterns and digestibility. Scanning electron microscopy was used to establish the three-dimensional characteristics of senescent wheat stems and the sequence of in vivo cell wall digestion. In vitro fermentation was used to establish effects of treatment on digestion. Light microscopy was used to compare the relative differences of phloroglucinol and ruthenium red-positive material of adjacent sections of ammonium and sodium hydroxide-treated wheat stem. The characteristic tissues in cross sections of wheat stems described by light microscopy were clearly evident in scanning electron photomicrographs. Scanning microscopy revealed a smooth inner cuticle enclosing ground parenchymal tissues. Ammonium hydroxide ruptured the inner cuticle and separated contiguous ground parenchymal cells, but had no effect on vascular tissue, thick-walled sclerenchyma or outer cuticle and epidermal silica. Hydrolysis of cellular material began with the inner cuticle and surrounding ground parenchymal tissue and continued to the large vascular bundles. Ammonium hydroxide did not improve in vitro digestion in 48-h samples. Additional ground parenchymal hydrolysis was observed in scanning microscopy samples after 72 h. Light microscopy of cross sections showed phloroglucinol positive material (lignin) in all cell walls except phloem. Adding either ammonium or sodium hydroxide solutions (4%) produced less dense, more diffuse lignin staining. Only 10% sodium hydroxide separated thick walled sclerenchyma. Ruthenium red-positive material (pectin) was removed by ammonium. Treating wheat straw with 3.2% ammonium hydroxide increased slightly the amount of ground parenchyma digested but had no effect on the highly lignified sclerenchymal and vascular tissues or outer cuticle and epidermis. Copyright © 1982. American Society of Animal Science. Copyright 1982 by American Society of Animal Science.