The effect of the rumen washing mechanism in sheep differs with concentration and size of abrasive particles

Measures of tooth wear have widespread use as proxies in palaeobiological reconstructions. In order to apply these proxies, an understanding of potential influence factors on wear is important. The processes during the digestion in the ruminant organism lead, possibly inadvertently, to a washing of material before it is regurgitated for rumination chewing. Therefore, ruminants might experience less tooth wear from external abrasives such as dust and grit, which can be washed off, compared to nonruminant herbivores. Details of the washing mechanism, including its efficiency in relation to abrasive size, have not been explored so far. Here, we describe the location and quantity of external abrasives in the gastrointestinal tract of sheep fed seven diets containing external silica abrasives varying in concentration (0, 4, and 8%) and size (4, 50, and 130 μm). As typical for ruminants, external abrasives accumulated mainly in the fourth stomach section, the abomasum. Compared to the diet, the dorsal rumen contents – from where material for regurgitation and rumination is recruited – were depleted of external abrasives for the 130 μm silicates, and for the 8% concentration of 50 μm silicates, but not for the 4 μm silicates or the 4% concentration of 50 μm silicates. These results suggest that the rumen washing mechanism is probably more protective against abrasion from grit and sand, and potentially less efficient against fine dust. •External abrasives ingested with the diet are washed off rumen contents.•This protects teeth from abrasion during rumination.•The effect is most distinct for large abrasives and less for very fine abrasives.•Abrasive effects on teeth should differ between ruminants and nonruminants.