Although roughages are the main components of diets for ruminants their endogenous enzymes cannot digest lingocellulosic feedstuffs but is carried out by the rumen microbial population which comprises of bacteria, protozoa and fungi. Their main function in the rumen is the fermentation of feeds which yields energy to the host animal in the form of short chain fatty acids. Recent interest in the efficient utilisation of roughage diets has led to an increase in the use of the gas production (GP) technique due to the advantage of studying fermentation kinetics. This technique provides useful data on digestion kinetics of both soluble and insoluble fractions of feedstuffs. Several GP approaches have been developed including the use of glass syringes (Menke et al., 1979; Blümmel et al., 1997) which appears to be the most suitable for use in developing countries. The objective of this experiment was to evaluate the effect of defaunating the rumen of sheep on the amount of GP from wheat straw, alfalfa hay, cottonseed meal and barley grain.