Ruminants like cows have evolved an unusual way of digesting their food: they swallow plants, chew them roughly, then swallow the half-chewed mash before regurgitating it repeatedly and continuing to chew. This has obvious advantages, as a research team including the University of Göttingen has shown: regurgitated soft food contains far less solid particles, sand and dust than the food they first ate.
This process also protects the teeth from being crushed during the chewing process. This may explain why the crowns of the teeth of ruminants are less pronounced than those of other herbivores. The results have been published in the journal Proceedings of the National Academy of Sciences (PNAS).
The researchers fed four cows grass fodder mixed with sand for several days and took samples of regurgitated food pulp and feces. Then they measured the silicate content of each sample. Compounds of sand and grass are particularly abrasive to the teeth because of their hardness. Feces contained the same amount of silicates as grass forage mixed with sand, while regurgitated food contained much less.
The only explanation is that the silicates must have remained in the stomach, or more precisely, in the “rumen”. The rumen is the largest stomach chamber in ruminants and the place where food is fermented and broken down by microorganisms.
Because this strenuous chewing is partly done on the pulp of the food “washed” in the rumen, the teeth of ruminants wear less frequently than those of horses, for example. The latter chew their food thoroughly after ingestion, including the abrasive parts.
For the researchers, this observation makes sense because ruminant teeth have relatively low crowns. The digestion method means that the teeth stay functional for longer. It explains the distinctive shape of ruminant teeth: There was no evolutionary pressure to form more dental material.
“Our research explains a fundamental and little-studied aspect of food grinding in large herbivores, contributing to the understanding of dental function and development,” explains Professor Jürgen Hamel, from the Ruminant Nutrition Group at the University of Göttingen.
In addition to understanding the physiology of digestion, the finding is interesting for paleontologists: Teeth are well preserved as fossils and often provide the most important clues in reconstructing early herbivores and their ecology.
Sarah O. Valerio et al, Ruminant screening mechanism protects teeth from abrasive materials, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2212447119
Gordon D. Sanson, Re-evaluating Assumptions About the Evolution of Herbivorous Teeth, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2219060120
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