No ‘bypass’ in adult ruminants: Passage of fluid ingested vs. fluid inserted into the rumen in fistulated muskoxen (Ovibos moschatus), reindeer (Rangifer tarandus) and moose (Alces alces)

Abstract

In young ruminants, the reticular groove ensures that ingested milk is channelled past the forestomach to avoid malfermentation. It has been speculated that some adult wild ruminants, in particular browsing species, maintain a functional oesophageal (reticular) groove, that soluble nutrients can thus bypass the rumen, and that thus the energetic gain from the diet can be increased. We inserted a fluid marker (Co-EDTA) via cannula into the rumen and simultaneously fed a diet that contained a second fluid marker (Sm-EDTA), and analysed the faecal marker excretion patterns, in muskoxen (Ovibos moschatus, n=4 in two experiments each), reindeer (Rangifer tarandus, n=4 in a total of six experiments) and moose (Alces alces, n=1 in one experiment). In no case was the orally fed marker excreted dinstinctively earlier than the marker inserted into the rumen, which indicates that substantial bypass did not occur in these animals. However, differences between the three species in the excretion of the two markers from the rumen are consistent with hypothetical differences in the stratification of rumen contents. We suggest that effects previously ascribed to a "rumen bypass" in wild ruminants most likely reflect differences in the passage from the rumen. No 'bypass' in adult ruminants AbstractIn young ruminants, the reticular groove ensures that ingested milk is channelled past the forestomach to avoid malfermentation. It has been speculated that some adult wild ruminants, in particular browsing species, maintain a functional oesophageal (reticular) groove, that soluble nutrients can thus bypass the rumen, and that thus the energetic gain from the diet can be increased. We inserted a fluid marker (Co-EDTA) via cannula into the rumen and simultaneously fed a diet that contained a second fluid marker (Sm-EDTA), and analysed the faecal marker excretion patterns, in muskoxen (Ovibos moschatus, n=4 in two experiments each), reindeer (Rangifer tarandus, n=4 in a total of six experiments) and moose (Alces alces, n=1 in one experiment). In no case was the orally fed marker excreted dinstinctively earlier than the marker inserted into the rumen, which indicates that substantial bypass did not occur in these animals. However, differences between the three species in the excretion of the two markers from the rumen are consistent with hypothetical differences in the stratification of rumen contents. We suggest that effects previously ascribed to a "rumen bypass" in wild ruminants most likely reflect differences in the passage from the rumen.

The digestive morphophysiology of wild, free-living, giraffes

“…The advantage of rumen bypass is that loss of carbohydrate energy by fermentation is avoided. The mechanism of bypass as proposed by Hofmann (1989) is via the oesophageal (ventricular) groove, although there is some evidence from North American captive ruminants fed an artificial diet that this mechanism may not function in adults (Lechner et al, 2009). The groove is quite short in okapi (2-5cm) and giraffes (8cm) compared to that in cattle (20cm; Burne, 1939).…”

The relative plasma availabilities of ivermectin in reindeer (Rangifer tarandus tarandus) following subcutaneous and two different oral formulation applications

“…Ruminal bypass could be explained by the oesophageal groove closure directing the drug mixture directly to the abomasum. This explanation loses some credibility because ruminal bypass was found not to take place in adult reindeer [ 27 ]. The 8-month-old reindeer calves in the present study had recently been weaned; the end of lactation takes place typically 24 to 26 weeks after birth [ 28 ].…”

The effect of size and density on the mean retention time of particles in the reticulorumen of cattle (Bos primigenius f. taurus), muskoxen (Ovibos moschatus) and moose (Alces alces)

“…Feed intake and proximate composition of the different diets have already been reported (34) and are given in Table 2. Retention times of fluid and forage particle markers have been described previously for these animals (34,39) . In addition, we applied a set of plastic particle markers similar to those described by Kaske & von Engelhardt (18) and Kaske et al (19) .…”