The effect of chlorite delignification on digestibility of some grass forages and on intake and rumen microbial activity in sheep fed barley straw

Abstract

SummarySodium chlorite increased the degradability of fibre from a range of mature grass forages inoluding barley straw by 40–50 digestibility units when comparisons were made using ground (1 mm sieve) material incubated eitherin vitrowith cellulase or in nylon bags in the rumen. However, when fed to sheep, chlorite-treated barley straw was digested to a similar degree to untreated straw (49 and 57% respectively), but intake was significantly reduced (385 and 790 g/day respectively). The poorin vivoutilization of chlorite-treated straw coincided with high proportions of propionic to acetic acid in the rumen (0·85, cf. 0·28 with untreated feed) and absence of rumen fungi. Rumen pH and ammonia concentrations were not significantly different between diets. When incubated in nylon bags in the rumen of animals fed the corresponding diet, both untreated and treated straw (< 1 mm) were well colonized with micro-organisms, as measured by cystine accumulation which showed peaks on the fibres after 24 and 72 h. While large numbers of fungal sporangia were observed after 24 h incubation on digesta from untreated forage, no fungi could be detected on the chlorite-treated material. Cystine accumulation on the untreated straw after 72 h was not associated with a secondary growth of fungi.Although barley straw chaff, ground (< 1 mm) after treatment with chlorite, was highly degraded in nylon bags in the rumen and with cellulasein vitro, larger particles (1 cm) suspended in nylon bags in an animal fed chlorite-treated straw actually gained weight, probably due in part to the degree of microbial colonization.