On the role of higher plant and microbial lipases in the ruminal hydrolysis of grass lipids.

1. The galactolipids of heat-treated, 14C-labelled rye grass S24 administered intraruminally to a sheep fed on an autoclaved diet were rapidly catabolized. 2. When grass was homogenized with rumen contents devoid of higher plant lipases the grass galactolipids were rapidly metabolized, but were not metabolized when the rumen contents were boiled to destroy microbial galactolipases. 3. 14C-labelled monogalactosyldiglyceride, digalactosyldiglyceride and triolein were metabolized, with the release of 14C-labelled fatty acids when incubated with a homogenate (100 g/l) of grass or clover in rumen fluid from a starved sheep, but not when the rumen fluid was heat-treated to destroy microbial enzymes. 4. It is concluded that in the sheep the lipases of rumen micro-organisms play a major part in the ruminal degradation of ingested complex lipids of pasture.