Comparative digesta retention patterns in ratites

Abstract

Ratites differ distinctively in the anatomy of their digestive tract. For example, Ostriches (Struthio camelus) have a particularly long, voluminous colon and long paired caeca, Rheas (Rhea spp.) are characterised by a short colon with particularly prominent paired caeca, and Emus (Dromaius novaehollandiae) -have neither very prominent caeca nor a prominent colon. We tested whether digesta excretion patterns corresponded to these differences in anatomy, expecting Ostriches to have the longest and Emus the shortest digesta retention times, and Rheas possibly showing a selective retention of fluids observed in other birds and mammals with prominent caeca. We used 6 Ostriches (97-123kg), 5 Greater Rheas (R. americana, 22-27kg) and 2 Emus (32-34kg) fed a common diet of alfalfa pellets ad libitum in captivity. Intake per unit of metabolic body mass did not differ between Ostriches and Rheas but was significantly higher in Emus, which also displayed higher defecation frequencies and lower fiber digestibility. Mean digesta retention time for small fiber particles (2 mm) differed significantly among species ; Emu: 1.3-1.8h), but there were no differences between the retention of 2 mm or 8 mm particles or a solute marker within species. The shape of the marker excretion curves corresponded to digesta mixing in the digestive tract of Ostriches and Rheas but not Emus. The calculated dry matter gut fill (% of body mass) was significantly higher in Ostriches (1.6-1.8) than Rheas (0.3-1.0) and Emus (0.2). Ostriches had the highest, and Emus the lowest fecal dry matter concentration. These physiological findings match the differences in digestive anatomy and support the concept that in ratites, herbivory -and hence flightlessness -evolved repeatedly in different ways. ABSTRACT Ratites differ distinctively in the anatomy of their digestive tracts. For example, Common Ostriches (Struthio camelus, hereafter Ostriches) have a particularly long, voluminous colon and long, paired caeca; Rheas (Rhea spp.) are characterized by a short colon with particularly prominent paired caeca; and Emus (Dromaius novaehollandiae) have neither prominent caeca nor a prominent colon. We tested whether digesta excretion patterns corresponded to these differences in anatomy, expecting Ostriches to have the longest and Emus the shortest digesta retention times, and Rheas possibly showing a selective retention of fluids observed in other birds and mammals with prominent caeca. We used 6 Ostriches (97-123 kg), 5 Greater Rheas (R. americana, 22-27 kg), and 2 Emus (32-34 kg) fed a common diet of alfalfa pellets ad libitum in captivity. Intake per unit of metabolic body mass did not differ between Ostriches and Greater Rheas but was significantly higher in Emus, which also displayed higher defecation frequencies and lower fiber digestibility. Mean digesta retention time for small fiber particles (2 mm) differed significantly among species (Ostrich: 30-36 h; Greater Rhea: 7-19 h; Emu: 1.3-1.8 h), but there were no differences between the retention o...

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

“…All samples were immediately ovendried at 60 °C and later ground to 0.75 mm. Marker analysis was performed in a similar way as in previous studies (Frei et al 2015). For wet ashing we heated samples with 4 ml nitric acid (HNO 3 ) and 2 ml hydrogen peroxide with the microwave MLS 'START 1500' (MLS GmbH, Leutkich, Germany).…”

Methane emission by adult ostriches (Struthio camelus)

“…In fact, a predominance of reductive acetogenesis in nonruminant mammals has been suggested earlier by Jensen (1996). Given the pronounced differences in gastrointestinal anatomy, digesta passage kinetics and digestive efficiency between ostriches and another large ratite, the emu (Dromaius novaehollandiae) (Herd and Dawson, 1984;Frei et al, 2015), it would be interesting to compare the methane production between these two species; measurements on faeces from captive emus suggest that these ratites are no methane producers (Hackstein and Van Alen, 1996).…”

“…For Mn analysis, samples were wet ashed with 4 mL nitric acid (HNO 3 ) and 2 mL hydrogen peroxide with the microwave MLS 'START 1500' (MLS GmbH, Leutkich, Germany). The Mn was then determined by inductively coupled plasma optical emission spectrometer (model Optima 8000, Perkin Elmer, Rodgau, Germany) (Frei et al, 2015). The aD was calculated, for total collection, as the percentage of the respective intake not eliminated via faeces (Robbins, 1993), or after calculating the amount of faeces eliminated with the amount of Mn ingested and the faecal Mn concentration, assuming that all ingested Mn was eliminated via faeces.…”

“…When compared to herbivorous mammals of similar body mass (BM), ostriches are characterised by a similar gut capacity, food intake, food particle size reduction (via gizzard grinding), digesta passage times and food digestibility (Fritz et al, 2011(Fritz et al, , 2012Frei et al, 2015). Ostriches are kept as farm animals in many countries worldwide, nowadays mostly for earning profit from selling their meat (Cooper, 2007).…”

Decreasing methane yield with increasing food intake keeps daily methane emissions constant in two foregut fermenting marsupials, the western grey kangaroo and red kangaroo

“…A number of studies have demonstrated the negative correlation between DMI and MRT in ratites (Frei et al, 2015c), sloths (Vendl et al, 2015), ruminants (Clauss et al, 2007;Hammond et al, 2014) and macropods (Munn et al, 2008). In essence, a higher food intake leads to a faster passage of digesta through the digestive tract, mostly because of the limited capacity of the gut to expand.…”