Six plant species were compared in terms of their physical breakdown when eaten by sheep and when macerated: chickweed (Stellaria media (L.) Vill.), dandelion (Taraxacum officinale Weber), dock (Rumex obtusifolius L.), ribwort (Plantago lanceolata L.), spurrey (Spergula arvensis L.) and perennial ryegrass (Lolium perenne L.). In two experiments at Aberystwyth in 1985 and 1986, the species were artificially dried and fed to lambs as the total diet. In another experiment in 1987, they were fed fresh, in 1·5 min meals, to yearling sheep.

Perennial ryegrass was more difficult to break down than the dicotyledonous species, judging by the particle size distribution in macerated and in chewed material and in the rumen contents and from the rather long time the sheep spent eating and ruminating per 100 g dry matter (DM) intake and the rather high fibrosity index. The width of some of the smaller ryegrass particles in the rumen was such that they must have contained only a single vein. Spurrey was readily broken down by macerating and by chewing and a relatively short time was spent eating and ruminating per 100 g DM intake. The shape of spurrey particles in the rumen was quite similar to that of stemmy ryegrass particles and the fibrosity index of spurrey was high. The breakdown of chickweed was similar to that of spurrey, but the fibrosity index of chickweed was lower. Accumulation of DM in the caecum appeared particularly pronounced in sheep fed ribwort or dock. The dock particles in the rumen typically had a low ratio of length to width and it seemed that dock particles did not need to be reduced in size as much as ryegrass particles before passing out of the rumen.