Effects of gaseous ammonia on chemical and structural features of cell walls in spring barley straw

Abstract

Dry matter degradability at 72 h rumen incubation was 268 and 376 g kg −1 dry matter for untreated and ammonia-treated stems, respectively, of spring barley ( Hordeum vulgare L.) straw. Electron micrographs of stem tissues showed that microbial degradation of parenchyma and sclerenchyma cell walls was increased following ammonia treatment. This was partially the result of promoted access by rumen microorganisms to the luminal surface of tissue cells associated with alteration in the fragility of a thinner, rigid layer covering the inner surface. Substantial cracking of the inner parenchyma layers was also observed for ammonia-treated stems. No differences in the amount of soluble sugars extracted was detected between untreated and ammonia-treated straws, although periodic acid-thiocarbohydrazide-silver proteinate-stained sections of the internodes showed an apparent reduction in the reaction of polysaccharides following ammonia treatment. Infrared spectroscopy showed that bands at 1725 and 1250 cm −1, attributable to acetyl groups, were decreased in the insoluble fraction of ammonia-treated straw, while the absorption band at 1650 cm −1 was increased, but only in the aqueous extract of the same material. Changes in chemical and structural features of cell walls after ammonia treatment are discussed in relation to the improvement in rumen degradability of spring barley straw.