The Ruminant sorting mechanism protects teeth from abrasives

Abstract

Dental wear due to ingestion of dust and grit has deleterious consequences. Herbivores that could not wash their food hence had to evolve particularly durable teeth, in parallel to the evolution of dental chewing surface complexity to increase chewing efficacy. The rumen sorting mechanism increases chewing efficacy beyond that reached by any other mammal and has been hypothesized to also offer an internal washing mechanism, which would be an outstanding example of an additional advantage by a physiological adaptation, but in vivo evidence is lacking so far. Here, we investigated four cannulated, live cows that received a diet to which sand was added. Silica in swallowed food and feces reflected experimental dietary sand contamination, whereas the regurgitate submitted to rumination remained close to the silica levels of the basal food. This helps explain how ruminants are able to tolerate high levels of dust or grit in their diet, with less high-crowned teeth than nonruminants in the same habitat. Palaeo-reconstructions based on dental morphology and dental wear traces need to take the ruminants’ wear-protection mechanism into account. The inadvertent advantage likely contributed to the ruminants’ current success in terms of species diversity.

Comparative study of feeding and rumination behaviour of goats and sheep fed mixed grass hay of different chop length

“…In fact, a hypothesis linked to abrasiveness contamination of natural diet matches well with the observed pattern. Besides other, well‐described advantages, the ruminant forestomach physiology also represents a mechanism that washes off dust, sand or grit from the ingested feed prior to rumination (Hatt, et al, 2019; Valerio et al, 2022). Free‐ranging ruminants have been reported to ingest significant levels of soil inadvertently with their diet (Beyer et al, 1994; Fannin et al, 2022; Hummel et al, 2011; Madden, 2014; Sanson et al, 2017).…”

Masticatory myology of the llama (Lama glama, Camelidae) and comparisons with other camelids and euungulates

“…Mandibular efforts and stress resistance in camelids were also described as intermediate between ruminants and perissodactyls (Zhou et al, 2019). These features were associated with relaxed chewing pressures due to the softening and washing of the ingesta resulting from rumination (Hatt et al, 2021; Hendrichs, 1965; Janis, 1983; Popowics & Herring, 2006; Sasaki et al, 2001; Valerio et al, 2022; Zhou et al, 2019). Furthermore, when the mass ratio between masticatory muscles and mandible is computed, the values for Lama glama (≈152%; see Table 1) are between those presented by Hendrichs (1965) for ruminants (≈130%) and those of other herbivores (horses and rodents; ≈240%), although closer to the former group.…”

Teeth and the gastrointestinal tract in mammals: when 1 + 1 = 3

“…Additionally, the initial fermentation that occurs before digesta are submitted to rumination softens the material to some degree, so that less energy is required for comminution [104]. Even more, the sorting in a fluid medium washes off external abrasives like grit or dust, removing an important cause of dental wear from the material re-submitted to rumination [122][123][124][125]. Plausible consequences of these effects are a shift of the main load of mastication from ingestive mastication to ruminant mastication (to save chewing effort and minimize wear due to external abrasives) [126], a shifting from a less thorough, 'sloppy' chewing pattern during ingestion to a consistent, homogenous chewing pattern during rumination [127], or the fact that rumination contributes more to particle size reduction than ingestive mastication [128,129].…”