Sulphur availability and microbial fermentation in the fauna-free rumen.

The concentration of H2S and rate of feed digestion, VFA and methane production in the rumen were measured in sulphur deficient (-S) and S supplemented (+S) sheep while fauna-free (-P) and after refaunation (+P). The concentration of rumen H2S was increased by S supplementation but was not affected by the presence of protozoa. When fauna-free, -S sheep had reduced rates of feed digestion (30 v 48%/d), acetate synthesis (35 v 115 g/d) and methane synthesis (0.4 v 7.4 g C/d) compared to +S sheep and up to 36% (v/v) of total rumen gas was H2. When these sheep were given a single dose of 8.8 g Na2SO4, the proportion of methane increased and the proportion of H2 in rumen gas decreased. After refaunation of sheep, their rates of feed digestion, VFA production and methane production were higher and were not affected by the level of S. From this differential response to S deficiency by -P and +P sheep, it is concluded rumen protozoa increase the availability of S to other rumen microbes. This is probably because they degrade protein through to peptides and amino acids.