Digestion of grass lipids and pigments in the sheep rumen

Abstract

1. Digestion of grass lipids and pigments in the rumen of the sheep has been studied during starvation and following the administration of 14 C-labelled grass. 2. Both galactolipids contained in chloroplasts are rapidly degraded, although mono-galactosyldiglycerides disappear faster than digalactosyldiglycerides. It was concluded that rumen micro-organisms are mainly responsible for this degradation, although grass itself also contains enzymes which can degrade galactolipids. 3. Rumen contents can degrade added 14 C-labelled mono- and digalactosyldiglycerides in vitro at a rate sufficient to account for the disappearance of galactolipids in the intact rumen. The initial enzyme attack is probably a successive deacylation to give monogalactosylglycerol and digalactosylglycerol. 4. Most of the chlorophyll pigments are rapidly converted into phaeophytins by loss of magnesium. A small proportion of chlorophyll a and more of chlorophyll b remains intact even after 24 h starvation. On the other hand, about half the phaeophytin undergoes further rapid decomposition to yield phylloerythrin. 5. Although the grass phospholipids are extensively degraded, β-carotenes and many non-polar compounds, e.g. steroids, appear to undergo little change in the rumen.