Relations between fibre and water soluble carbohydrate contents of pasture species and their digestibility and voluntary intake by sheep

Abstract

Neutral detergent fibre (NDF), acid detergent fibre (ADF) and water soluble carbohydrate (WSC) levels were determined on 80 samples of known apparent dry matter digestibility (DMD) and voluntary intake of dry matter (DMI). The pastures consisted of regrowths of six species: Trifolium repens (white clover cv. Grasslands Huia), Lolium perenne x L. multiflorum (short rotation ryegrass c.v Grasslands Manawa), Lolium perenne (long rotation ryegrass cv. Grasslands Ariki), Lolium perenne (perennial ryegrass cv. Tasmania No. I), Dactylis glomerata (cocksfoot cv. Currie) and Dactylis glomerata (cocksfoot cv. Grasslands Apanui), cut eight times between May 1969 and August 1970. Overall, white clover had a lower NDF and a lower WSC content than the ryegrasses but both groups had similar ADF contents. Cocksfoots had higher NDF and ADF, and lower WSC contents than the ryegrasses. NDF and ADF could be used to predict the DMD of all species in all seasons with residual standard deviations (RSD) of 3.0 and 3.2 DMD units (per cent) respectively. No significant relations (P < 0.05) were present between DMD and WSC content. Seasonal differences were present in the relations between DMI and chemical composition. The RSD of the overall regressions of intake with NDF, ADF, and WSC contents were 9.3, 9.4, and 8.9 DMI units (g/day/kg0.75) respectively. Within seasons, DMI was best predicted by regressions with detergent fibre content and here the RSD had a range of 3.4 to 5.2 DMI units. Within species over all seasons, DMI was predicted best by regressions with WSC content and the RSD had a range of 5.7 to 7.9 DMI units. The usefulness of the chemical composition measurements in explaining the reason for the low intakes, previously found with winter pasture, is discussed.