Rumen microorganisms have variable requirements for a nitrogen source. Cumulative gas production (Theodorou et al., 1994) is often measured using media containing both ammonia (NH3) and mixed peptides (trypticase-TRYPT) to ensure that all microbes will have sufficient nitrogen (N) of the appropriate quality for growth and metabolism. This experiment was conducted to assess the effect of N source in the medium on the fermentation characteristics of citrus pulp, which was used as being representative of a readily fermentable carbohydrate.