The retention of ingesta in the digestive tract is a major characteristic of herbivorous animals. We measured particle and fluid mean retention times (MRT) in 13 lowland tapirs (Tapirus terrestrus) and 5 Malayan tapirs (Tapirus indicus) from five zoological institutions on their usual zoo diet and 2 lowland and 4 Malayan tapirs additionally on roughage-only diets (total n of trials = 24) with cobalt-EDTA as fluid and chromium-mordanted fibre (<2 mm) as particle markers MRT for fluid and particles averaged 42 +/- 16 11 and 55 +/- 18 h in lowland and 40 13 It and 56 14 h in Malayan tapirs. In a General Linear Model, neither Tapir species. body mass or diet (characterised by the proportion of roughage) was significantly related to MRT, but dry matter intake was, with a steep decline in MRT with higher intake levels. Compared to other hindgut fermenters, tapirs have a low defecation frequency, which might be linked to their comparatively low food intake Their gastrointestinal capacity (in dry matter 1 63 +/- 063% of body mass) is similar to that calculated for horses A comparison of the difference in fluid and particle MRT in large hindgut fermenters (horses, rhinoceroses, elephants, and the tapirs of this study) shows that longer absolute particle MRT are linked to shorter relative fluid MRT, possibly indicating a more thorough 'washing' of particulate ingesta with digestive fluids at longer particle MRT. The only outlier to this general pattern, with an exceptionally high difference between fluid and particle MRT. indicating a particularly efficient ingesta washing, is the white rhinoceros (Ceratotherum simum) If possible, results of this study should be compared to findings in tapiis on natural diets (C) 2010 Elsevier Inc All rights reserved