Ruminants like cows have developed an unusual way of digesting their food: they ingest plants, give them a rough chewing and then swallow the half-chewed mash before regurgitating it repeatedly and continuing to chew. This has clear advantages, as a research team including the University of Göttingen has shown: the regurgitated mushy food contains much less hard grit, sand and dust than the food that they first ingested.
This process also protects the teeth from being ground down during the chewing process. This may explain why the crowns of the teeth of ruminants are less pronounced than those of other herbivores. The findings have been published in the journal Proceedings of the National Academy of Science (PNAS).
The researchers fed four cows grass feed mixed with sand for several days and took samples of the regurgitated food pulp and feces. They then measured the silicate content of each sample. The compounds from sand and grass are particularly abrasive to teeth because of their hardness. The feces contained about the same amount of silicates as the grass feed mixed with sand, whereas the regurgitated food contained significantly less.
The only explanation is that the silicates must have stayed in the stomach, or more precisely in the "rumen." The rumen is the largest stomach compartment in ruminants and the place where food is fermented and broken down by microorganisms.