Bioassay methods to estimate the digestibility of forages for ruminants, such as the in vitro digestibility technique (Tilley and Terry, 1963), the nylon bag technique (Ørskov et al., 1980) and the gas production methods of Menke and Steingass (1988) and Theodorou et al. (1994), require rumen fistulated animals, either to provide a suitable in situ environment or to provide rumen liquor as a source of inoculum. Not only is establishing and maintaining fistulated animals expensive, but fistulation is an invasive technique which is increasingly discouraged on animal welfare grounds. There is therefore a need to find an alternative to rumen liquor as a source of micro-organisms for bioassays.
Although the Tilley and Terry (1963) technique is widely used, it is limited by being an end-point digestibility method. Ørskov et al. (1988) showed that intake of forages and their rate of digestion in the rumen are more correlated than intake and digestibility. Thus, since 1988, there has been much interest in determining rate of rumen degradability using the nylon bag technique (Huntington and Givens, 1995). However, as indicated earlier, this in vitro technique requires fistulated animals. Recently Sileshi et al. (1996) showed that the in vitro gas production technique of Theodorou et al. (1994), offers a possibility of assessing rate of rumen degradation.
The purpose of the present experiment was to compare rumen liquor and faeces as sources of inoculum in the gas technique of Theodorou et al. (1994).