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Abstract: In domestic ruminants, the stratification of forestomach contents – the results of flotation and sedimentation processes – is an important prerequisite for the selective particle retention in this organ. A series of anatomical and physiological measurements suggests that the degree of this stratification varies between browsing and grazing wild ruminants. We investigated the forestomach contents of free-ranging mouflon and roe deer shot during regular hunting procedures. There was no difference between the species in the degree by which forestomach ingesta separated according to size due to buoyancy characteristics in vitro. However, forestomach fluid of roe deer was more viscous than that of mouflon, and no difference in moisture content was evident between the dorsal and the ventral rumen in roe deer, in contrast to mouflon. Hence, the forestomach milieu in roe deer appears less favourable for gas or particle separation due to buoyancy characteristics. These findings are in accord with notable differences in forestomach papillation between the two species. In roe deer, particle separation is most likely restricted to the reticulum, whereas in mouflon, the whole rumen may pre-sort particles to a higher degree. The results suggest that differences in forestomach physiology may occur across ruminant species. [Copyright &y& Elsevier]

Abstract: Retention time of food in the digestive tract is a major aspect describing the digestive physiology of herbivores. Differences in feed retention times have been described for different ruminant feeding types. In this study, a dominantly grazing desert ruminant, the addax (Addax nasomaculatus), was investigated in this respect. Eight animals with a body weight (BW) of 87±5.3 kg on an ad libitum grass hay (Chloris gayana) diet were available. Co-EDTA and Cr-mordanted fibers (<2 mm) were used as pulse-dose markers. Mean retention time (MRT) in the digestive tract was calculated from faecal marker excretion. Average daily intake of the addax was found to be 1.7 kg dry matter (DM) or 60±8.3 g DM/kg BW0.75. The MRT of fluid and particles in the reticulo-rumen (MRTfluidRR and MRTparticleRR) were quantified to be 20±5.8 and 42±7.0 h respectively. When compared to literature data, MRTfluidRR was significantly longer than in cattle species, and MRTparticleRR was significantly longer than in 11 taxa of all feeding types. The ratio of MRTparticleRR/MRTfluidRR (2.3±0.5) was found to be within the range described for grazing ruminants. The long retention times found in the addax can be interpreted as an adaptation to a diet including a high proportion of slow fermenting grasses, while the long retention time of the fluid phase can be interpreted as a consequence of water saving mechanisms of the desert-adapted addax with a potentially low water turnover and capacious water storing rumen. [Copyright &y& Elsevier]

Abstract: As gut capacity is assumed to scale linearly to body mass (BM), and dry matter intake (DMI) to metabolic body weight (BM0.75), it has been proposed that ingesta mean retention time (MRT) should scale to BM0.25 in herbivorous mammals. We test these assumptions with the most comprehensive literature data collations (n =74 species for gut capacity, n =93 species for DMI and MRT) to date. For MRT, only data from studies was used during which DMI was also recorded. Gut capacity scaled to BM1.06. In spite of large differences in feeding regimes, absolute DMI (kg/d) scaled to BM0.76 across all species tested. Regardless of this allometry inherent in the dataset, there was only a very low allometric scaling of MRT with BM0.14 across all species. If species were divided according to the morphophysiological design of their digestive tract, there was non-significant scaling of MRT with BM0.04 in colon fermenters, BM0.08 in non-ruminant foregut fermenters, BM0.06 in browsing and BM0.04 in grazing ruminants. In contrast, MRT significantly scaled to BM0.24 (CI 0.16–0.33) in the caecum fermenters. The results suggest that below a certain body size, long MRTs cannot be achieved even though coprophagy is performed; this supports the assumption of a potential body size limitation for herbivory on the lower end of the body size range. However, above a 500 g-threshold, there is no indication of a substantial general increase of MRT with BM. We therefore consider ingesta retention in mammalian herbivores an example of a biological, time-dependent variable that can, on an interspecific level, be dissociated from a supposed obligatory allometric scaling by the morphophysiological design of the digestive tract. We propose that very large body size does not automatically imply a digestive advantage, because long MRTs do not seem to be a characteristic of very large species only. A comparison of the relative DMI (g/kg0.75) with MRT indicates that, on an interspecific level, higher intakes are correlated to shorter MRTs in caecum, colon and non-ruminant foregut fermenters; in contrast, no significant correlation between relative DMI and MRT is evident in ruminants. [Copyright &y& Elsevier]