Abstract
Few information on the chemical constituents and the rumen degradation characteristics of cold weather-damaged rice straw (CDRS) was reported. The chemical composition, the 48 h dry matter loss (48h-DML), maximum potential dry matter degradability (MPDD) and degradation rate (DR) in the rumen of sheep were investigated for forty-seven samples of CDRS collectedin 1993 and their botanical fractions (leaf blade, leaf sheath and stem) showing different percentage of sterility and compared to those of the seven samples of normal rice straw (NRS) and their botanical fractions collected in Iwate prefecture in 1994. The stem tissues of CDRS and NRS were observed by a scanning electron microscopy. The proportion of stem in CDRS was increased, while those of leaf blade and leaf sheath were decreased with increasing the percentage of sterility. Differences in the proportion of the botanical fractions between CDRS and NRS were particularly larger in the stem and leaf sheath than in the leaf blade. Crude protein (CP) of CDRS increased with increasing the percentage of sterility, whereas neutral detergent fibre (NDF) was decreased, showing the maximum differences of 4.3 (CP) and 6.7% (NDF) units between CDRS and NRS. The concentrations of mono- and oligosaccharides and starch were less variable among the percentages of sterility of CDRS, but those were 1.8-1.7 and 5.9-4.3 times higher than in NRS, respectively. About 90% of the total amount of those constituents in the whole straw was attributable to those of the stem. Higher content of starch in stem was also consistent with observation of starch granule in the stem of CDRS with a scanning electron microscope. The increase of percentage of sterility gave higher 48-h DML and MPDD, and their differences between CDRS and NRS were 19.8-11.9% for 48-h DML and 20.4-12.6% units for MPDD. The 48-h DML of botanical fractions in CDRS was particularly high for stem (77.6-74.2%), followed by leaf blade (66.0-53.1%) and leaf sheath (56.8-55.2%) in which maximum differences compared to NRS were 12.8, 18.2 and 21.2% units, respectively. The DR of CDRS with high and middle percentage of sterility were increased ranging from 4.6 to 4.1%/h, respectively, while that of NRS was 3.0%/h. It was concluded that the chemical composition and the rumen degradation characteristics of CDRS were significantly varied by the extent of percentage of sterility which was associated with cold weather damage, and also the nutritive value of CDRS was remarkably higher than that of NRS.
