Rumination of different-sized particles in muskoxen (Ovibos moschatus) and moose (Alces alces) on grass and browse diets, and implications for rumination in different ruminant feeding types

Abstract

The obligatory, periodic regurgitation of forestomach material and its subsequent re-mastication is the hallmark of the most diverse extant large herbivore group, the ruminants. Although the process of rumination is well understood in domestic species, differences between free-ranging wild ruminant species, for example of different body size or different feeding type, remain speculative to date. Here we investigate the proportion of plastic particles of varying size (1, 10 and 20mm) and density (1.03, 1.20 and 1.44 mg/ml) that are recovered intact or ruminated-upon after insertion into the reticulorumen (RR) of domestic cattle (Bos primigenius f. taurus) on grass silage, and of muskoxen (Ovibos moschatus; n = 4) and moose (Alces alces; n = 2) both fed browse and grass diets. In the three species, the proportion of particles leaving the RR intact depended on particle size, with density showing no effect in this study. The major proportion of 1mmparticles was excreted intact, whereas intact 10-20mmparticles were only excreted sporadically, and not in all animals. Intact particles were mostly found in the initial samples after marker application, and mean retention times of intact particles were always shorter than those of ruminated particles. There were no differences between moose and muskoxen, but diet had a significant effect, with a higher proportion of 1mm particles ruminated upon on the grass diet in both species, indicating a higher 'filter-bed effect' with entrapment of small particles in a fibre mat in the RR on a grass diet. Given that less particles were ruminated on the grass diet, one could either assume that free-ranging browsers ruminate less than grazers on similar food intakes (or that they have higher food intakes at similar levels of rumination). The existing data on time-budgets of free-ranging ruminants, however, does not suffice to test these hypotheses. The fact that indication of a 'filter-bed effect' was also detectable in moose raises the question whether adaptations described in 'cattle-type' ruminants really serve to re-inforce the processes of RR contents stratification and the 'filter-bed', or whether they are not rather directed at other aims, such as maximizing microbial yield from the RR. Abstract 17The obligatory, periodic regurgitation of forestomach material and its subsequent re-18 mastication is the hallmark of the most diverse extant large herbivore group, the ruminants. 19Although the process of rumination is well understood in domestic species, differences 20 between free-ranging wild ruminant species, for example of different body size or different 21 feeding type, remain speculative to date. Here we investigate the proportion of plastic 22 particles of varying size (1, 10 and 20 mm) and density (1.03, 1.20 and 1.44 mg/ml) that are 23 recovered intact or ruminated-upon after insertion into the reticulorumen (RR) of domestic 24 cattle (Bos primigenius f. taurus) on grass silage, and of muskoxen (Ovibos moschatus; n=4) 25 and moose (Alces alces; n=2) both fed bro...

Comparative selective retention of particle size classes in the gastrointestinal tract of ponies and goats

“…The results of this study corroborate known differences in the selective retention of digesta particles in ruminants that lead to different‐sized faecal particles: large particles are rare in ruminant faeces and represent digesta fractions that escape the forestomach comparatively soon after ingestion; most particles are retained and submitted to repeated comminution via rumination (Lauper et al., ; Udén, ). Differences in MRT between large and small particles in the ruminant species were not only significant, but also of a magnitude (8–9 hr) that is relevant in terms of fermentative digestion (Hummel, Südekum, Streich, & Clauss, ).…”

“…Note the general similarity to Figure 2, and the inverse pattern in particle sizes in the ruminant. This is because particle sizes do not denote different ingested markers in this experiment, but different fractions of the same marker escaping the forestomach; in ruminants, the minor fraction of large particles that escapes rumination is typically excreted very soon after ingestion represent digesta fractions that escape the forestomach comparatively soon after ingestion; most particles are retained and submitted to repeated comminution via rumination (Lauper et al, 2013;Udén, 1978). Differences in MRT between large and small particles in the ruminant species were not only significant, but also of a magnitude (8-9 hr) that is relevant in terms of fermentative digestion (Hummel, Südekum, Streich, & Clauss, 2006).…”

Dry matter and digesta particle size gradients along the goat digestive tract on grass and browse diets

“…In line with this argument, Hooper and Welch () found that legumes change specific gravity faster than grasses. Larger particles that support a floating fibre mat for longer could be the reason why grass diets, irrespective of the forestomach physiology of the ruminant, trigger a more pronounced ‘filter bed effect’ where small particles are retained in the rumen due to entrapment in the mat (Clauss et al., ; Lauper et al., ). Hence, physiological adaptations in ‘cattle‐type’ ruminants to increase fluid flow through the rumen (Dittmann et al., ; Hummel et al., ) that also lead to a higher availability of low‐viscosity fluid in this organ, and physicochemical properties of grass itself, combine to result in the observed difference in rumen contents stratification between browsing and grazing ruminants.…”

Physiological adaptations of ruminants and their potential relevance for production systems

“…Based on those early observations, a theory was developed that linked the throughput of great amounts of a low-viscosity fluid in cattle-type ruminants to adaptations whose ultimate objective was considered to be the enhancement of the natural tendency of grass forage to stratify in the rumen, thus facilitating a more efficient selective particle retention, size reduction via rumination, and hence digestibility (Clauss et al, 2003;Clauss et al, 2008b). When this theory was tested experimentally, however, results indicated that the particle retention and sorting mechanism did not differ fundamentally between a moose-type and a cattle-type species, even though differences in rumen content stratification, rumen fluid viscosity, and the relative rumen fluid throughput could be demonstrated (Lechner et al, 2010;Clauss et al, 2011;Lauper et al, 2013).…”