PCR–denaturing gradient gel electrophoresis was not dif-
ferent between faunated and defaunated animals (Mosoni
et al., 2008a), suggesting that the decreased methano-
genesis might be due to a reduction in the amount of
hydrogen substrate. In the study of Morgavi et al. (2008),
the lower CH4 emission in defaunated animals was main-
tained for more than 2 years indicating that the changes
induced are stable. The elimination of the rumen protozoal
population to mitigate methanogenesis appears interesting,
but this option should be carefully evaluated in terms of
livestock performances. The absence of protozoa from the
rumen can have diverse effects on animals that can be
either negative or positive depending on the diet and the
type of production targeted. Up to now, however, practical
defaunation techniques are not available.