Results demonstrate a substantial reduction in the nutritional value of dried versus fresh rice plants, and it is clear that drying converts forage with a moderate nutritional value into one with a low quality. While fresh rice plants contained higher levels of Si in the ADF fraction, and less Si in the ND extracted ADF, than the same plant after drying, which may have been associated with higher in vitro gas production of fresh straws at 4, 24 and 72 h of fermentation, total Si and its fraction within the fiber matrix were not predictive of in vitro gas production from i39 field samples of rice straw, probably because the location of the Si in the fiber is not predictive of digestibility of OM. This is strongly supported by our results, which also showed that rice plants grown in Si free or Si containing hydroponic media had similar in vitro gas production per unit OM. The general lack of impact of Si levels, or locations in the fibre matrix, of rice plants on in vitro gas production in our three experiments demonstrate that Si is not causative to the low fermentability of rice straw OM.