The rumen washes off abrasives before heavy-duty chewing in ruminants

Abstract

Based on comparative mandibular anatomy, observations of chewing behaviour, chewing forces and dental microwear, it has been suggested that an additional effect of the ruminant digestive strategy could be a reduction of both the required chewing load and tooth wear ruminants are exposed to. This effect is hypothesized to be the result of digestion, mixing, and digesta sorting prior to regurgitation for rumination, which might both soften the material and wash off external abrasives such as sand, grit and dust. Putatively, these external abrasives would thus be trapped in the (fore)stomach and excreted via the faeces. We investigated the location of sand in the stomach of goats fed diets containing phytoliths and sand for several months. The contents of the stomach section from where rumination material is recruited were comparatively depleted of sand. Sand mainly accumulated in another stomach section, the abomasum, without causing clinical problems. A certain phytolith content should hence affect ruminants and non-ruminant herbivores somewhat alike; however, a certain external abrasives content should affect ruminants less than non-ruminants. Results from feeding experiments as well as tooth wear studies support this hypothesis, and caution against the default use of dental anatomy and wear as taxon-free environmental proxies in paleobiology.