Ruminants show a special behavior when eating: They swallow their plant food roughly chewed, then regurgitate it several times and continue chewing. This has a decisive advantage, as a research team with participation from the University of Göttingen has shown: The regurgitated food mush contains fewer hard silicates from sand and dust than the food initially ingested. As a result, the teeth are not ground down as much during chewing. This may explain why ruminants’ dental crowns are less pronounced than those of other herbivores. The findings appeared 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 slurry and the feces. They then determined the content of silicates. These compounds from the sand and grass particularly cause abrasion of the teeth because of their hardness. The feces contained about as much silicates as the sandy grass food, whereas the regurgitated food mash contained significantly less. The silicates therefore remain in the stomach, or more precisely in the rumen. This is the part of the stomach where the food is broken down by microorganisms.
Because the laborious chewing is partly shifted to food pulp that has been -washed- in the rumen, the teeth of ruminants are less worn than those of horses, for example. The latter chew their food completely after ingestion, including the abrasive parts. For the researchers, the observation fits with the fact that ruminants have comparatively low tooth crowns. Due to the power of rumening, the teeth remain functional longer. This influences their evolution: there is no pressure to form more tooth material.
-The study clarifies a little-noticed but fundamental aspect of food grinding in large herbivores and contributes to the understanding of the function and evolution of teeth-, explains Jürgen Hummel from the Department of Ruminant Nutrition. In addition to understanding the physiology of digestion, the result is interesting for paleontology: because of their good fossil record, teeth often provide the most important clues in reconstructing early herbivores and their environment.
A commentary in PNAS refers to the results and discusses the topic further:
Sanson G. D. Reassessing assumptions about the evolution of herbivore teeth. PNAS 2023. DOI : 10.1073/pnas.2219060120
Original publication: Valerio et al. The Ruminant sorting mechanism protects teeth from abrasives. PNAS 2023. DOI: 10.1073/pnas.2212447119
