The dissociation of the fluid and particle phase in the forestomach as a physiological characteristic of large grazing ruminants: an evaluation of available, comparable ruminant passage data

Abstract

Whether differences in digestive physiology exist between different ruminant feeding types has been an ongoing debate. In this regard, potential differences in ingesta retention have been understood to be of particular importance. We analyzed a data pool in which only mean retention time (MRT) data for the ruminoreticulum (RR) were collated that were obtained using comparable techniques with either chromium or cobalt EDTA as a fluid marker and/or with chromium-mordanted fiber of less than 2 mm in size as a particle marker. Data were compared using one averaged value per species. In general, the paucity of species in such a collection is striking and does not allow-in contrast to earlier statements-any final conclusions regarding the influence of body weight (BW) or feeding type on ruminant MRTs. In particular, there was no significant correlation between MRTparticlesRR or MRTfluidRR and BW, neither in the interspecific nor in the intraspecific comparisons, and no difference between the feeding types. The trend that indicates longer MRTparticlesRR in grazers is based on too few species to be conclusive. Small browsers seemed to have shorter MRTfluidRR than similar-sized grazers. In contrast, there was a trend for large grazers to have shorter MRTfluidRR than large browsers. In direct pair-wise comparisons between cattle and the browsers giraffe, moose, and okapi, the latter difference was significant. Cattle also had the highest relative RR fluid outflow rates among the species investigated. This is in accord with the observation that grazers have larger omasa, a major function of which is water-reabsorption distal to the RR. Grazers seem to have longer MRTparticlesRR per unit MRTfluidRR, and cattle are particular outliers in this respect. It is hypothesized that potentially shorter MRTfluidRR in large grazers and higher relative outflow rates are linked to a higher saliva production and a lesser viscosity of both saliva and RR fluids. A constant supply of a fluid phase of low viscosity is proposed to be the prerogative for the physical mechanisms of flotation and sedimentation that result in the stratification of RR contents and its selective particle retention typical for large grazing species

Nutritional content of savanna plant foods: implications for browser/grazer models of ungulate diversification

“…One possible explanation for the apparent contradiction here is that fiber digestibility and overall nutritional quality of the diet may not be the primary determinant for achieving differential retention times. Alternative hypotheses for the evolution of longer rumen retention in grazers were put forward based on differences in particle sizes into which browse and grass are broken down in the digestive tract, differences in fluid dissociation between these food types, and perhaps most importantly, grass stratification and formation of a fibrous raft in the rumen (Owen-Smith 1982;Clauss and LechnerDoll 2001;Clauss et al 2002Clauss et al , 2003Clauss et al , 2006. Thus, if at all, differences in physical, rather than biochemical, properties of grass and browse may have provided the basis for diversification of ungulate feeding styles and associated stomach physiology (see Clauss et al 2003).…”

“…Ideally, testing differential digestibilities requires in vivo measurements, but controlled feeding experiments with the variety of diets used in this study, representing similar spatiotemporal resolutions, are clearly impractical, especially for the diversity of ungulates found across the savanna. Indeed, the constraint common to all studies of ungulate nutritional physiology is the small number of taxa for which reliable data are available (see Clauss et al 2006). Many previous approaches have relied on ADF as a proxy for digestibility, but this fraction is in fact weakly correlated with DMD, explaining only between 1 and 20% of the variation therein (e.g., Moore and Coleman 2001).…”

Digesta retention patterns of solute and different-sized particles in camelids compared with ruminants and other foregut fermenters

“…This process is not restricted to ruminants as it can also be found in some NRFF and other digestion types (Müller et al 2011). Within ruminants, species differ in rumen fluid throughput and the degree of digesta washing (Clauss and LechnerDoll 2001;Clauss et al 2006;Dittmann et al 2015;Hummel et al 2015), which led to the classification of 'cattle-' and 'moose-type' ruminants. Therefore, the finding that 'cattle-' and 'moose-type' ruminants differ significantly in the SF 2mm/solute FS (Fig.…”

Comparative investigations on digestion in grazing (Ceratotherium simum) and browsing (Diceros bicornis) rhinoceroses

“…On a physiological level, an effective particle retention was postulated to be a particularly adaptive evolutionary feature in grazers (Kay et al 1980;Foose 1982). This is explained by the higher proportion of slow fermenting fiber in grass compared to browse (Short et al 1974;Foose 1982;Hummel et al 2006), and has been described for ruminants (Clauss et al 2001;Clauss et al 2006c). Furthermore, differences in tooth morphology can potentially lead to a decrease in food comminution in browsing herbivores leading to larger fecal particles in browsing ruminants (Clauss et al 2002b) and macropods (Lentle et al 2003).…”