Rumen dry matter degradability and apparent digestibility of variously treated rice hulls

Rice hulls from Hungary, Colombia, and Cambodia were used for measuring with the nylon bag method the dry matter degradability in the rumen of sheep. After 48 h rumen incubation time the dry matter loss varied between 10.0 and 27.7%. The 48 h rumen dry matter loss of rice hulls from Hungary increased from 14.0 (untreated control) only to 17.9, 20.1, and 17.0% after chemical treatment with 2% NaOH, 4% CaO, and 4% urea, respectively. gamma-irradiation with doses of 0, 0.1, 0.25, 0.5, 1, and 2 MGy effected rumen dry matter losses of unground rice hulls from Hungary of 6.4, 14.5, 13.5, 21.3, 37.1, and 70.5%. The apparent digestibility of organic matter of untreated rice hulls from Hungary amounted to 19.2%, as found in tests with wethers. The main reasons of low digestibility and the negligible effect of chemical treatments are the high contents of lignin (ca. 15%) and silica (up to 23% of the dry matter). Therefore rice hulls are not suitable as feedstuff for ruminants.