Although foregut fermentation is often equated with rumination in the literature, functional ruminants (ruminants, camelids) differ fundamentally from non-ruminant foregut fermenters (e.g. macropods, hippos, peccaries). They combine foregut fermentation with a sorting mechanism that allows them to remasticate large particles and clear their foregut quickly of digested particles; thus, they do not only achieve high degrees of particle size reduction but also comparatively high food intakes. Regurgitation and remastication of stomach contents have been described sporadically in several non-ruminant, non-primate herbivores. However, this so-called ‘merycism’ apparently does not occur as consistently as in ruminants. Here, to our knowledge we report, for the first time, regurgitation and remastication in 23 free-ranging individuals of a primate species, the foregut-fermenting proboscis monkey (Nasalis larvatus). In one male that was observed continuously during 169 days, the behaviour was observed on 11 different days occurring mostly in the morning, and was associated with significantly higher proportions of daily feeding time than on days when it was not observed. This observation is consistent with the concept that intensified mastication allows higher food intake without compromising digestive efficiency, and represents an expansion of the known physiological primate repertoire that converges with a strategy usually associated with ruminants only.

This longitudinal study aimed to identify risk factors for the incidence and progression of radiographic knee osteoarthritis (OA). We examined the inhabitants of Miyagawa village aged ≥65 years every two years between 1997 and 2007. Anteroposterior radiographs of both knees were graded for OA using the Kellgren-Lawrence (K/L) grading system. Knee OA was defined as grade ≥2. We recorded the incidence of knee OA among participants in whom both knees changed from K/L grades 0 or 1 to ≥2 over a four-year follow-up period. We also recorded the progression of knee OA using this threshold among patients in whom one or both knees changed from K/L grades 2 or 3 to any higher grade over the follow-up period. Baseline data obtained from standard questionnaires, physical findings and X-rays included age, gender, body mass index (BMI), osteoporosis, Heberden’s nodes, knee range of motion (ROM), knee pain and cigarette smoking. The rates of incidence and progression of knee OA among 360 participants (241 women, 119 men) who fulfilled the study criteria were 4.0 and 6.0% per year, respectively. Female gender (odds ratio [OR] 2.849, 95% confidence interval [CI] 1.170–6.944) and high BMI (OR 1.243, 95% CI 1.095–1.411) were significantly associated with the incidence of knee OA, and restricted knee ROM (OR 0.941, 95% CI 0.892–0.992) was significantly associated with knee OA progression. Patients with a low knee ROM relative to grade of radiographic knee OA require more careful follow-up than those with a higher ROM.