This study was conducted to determine ruminal degradation kinetics of DM, NDF and ADF and in vitro digestibility of some range species. Forage samples (Vicia villosa, Bromus tomentellus, Hordeum bolbusum, Festuca ovina, Agropyron tauri, Agropyron trichophorum, Prangus ferulacea, Ferula orientalis, Lathyrus L. and Taeniatherum L.) were collected at the pre-flowering stage on the same date by plotting from natural pastures of Kurdestan province of Iran. Four Varamini rams fitted with rumen fistula were used to determine in situ disappearance characteristics of forage samples. There were differences (P<0.05) for DM and OM digestibility among range species. Highest mean was for P. ferulacea and lowest one for F. ovina. Comparison between in situ and in vitro was made which showed differences (P<0.05) between the two methods. However there was a close relationship between the two methods (r2=0.91), therefore allowing in vitro method to be used for predicting digestibility of feedstuffs. In situ results showed that the effective DM, NDF and ADF degradability of ten pasture forages were different (P<0.05). The effective DM degradability at a ruminal outflow rate of 0.02/h was highest for P. ferulacea and lowest for F. ovina. The highest mean effective NDF degradability was for P. ferulacea and lowest one for H. bolbusum. The effective ADF degradability was highest for P. ferulacea while the lowest for F. ovina. In conclusion, the rate and extent of ruminal cell wall degradation were observed to be different among range species and must be considered as main parameters in ration formulation for ruminants, and also in physical fill & intake capacity models as well
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