Digesta retention patterns in geese (Anser anser) and turkeys (Meleagris gallopavo) and deduced function of avian caeca

Abstract

Although it is well-known that retrograde transport of urine fills the caeca of birds with fluid and small particles, the function of avian caeca is still not fully understood. We measured mean retention times (MRT) of solute (cobalt-EDTA, Co), small particle (<2mm, chromium-mordanted fibre, Cr) and large particle (8mm, cerium-marked fibre, Ce) markers in geese (Anser anser) and turkeys (Meleagris gallopavo) fed alfalfa pellets ad libitum. Intake did not differ between species. Turkeys had longer MRT for all markers (Co: 10.4 vs. 3.2h; Cr 23.3 vs. 2.9h; Ce 9.5 vs. 2.1h), achieved a higher fibre digestibility, and had a higher calculated dry matter gut fill. Thus, geese and turkeys correspond to the typical dichotomy of good fliers vs. poor fliers/flightless species in avian herbivores. Because uric acid is fermented much faster by microbes than fibre, the ultimate cause of short-MRT digesta retention in avian caeca as in geese is possibly rather uric acid than fibre fermentation. The numerical differences between marker MRT in geese correspond to a colonic separation mechanism that delays the excretion of fluids more than small and again more than large particles. In contrast to geese, turkeys excreted solid and liquid (caecal) faeces. Liquid faeces contained less fibre and more crude protein than solid faeces and accounted for the excretion of 7, 25 and 34% of Ce, Co and Cr markers. Marker excretion patterns and MRT for liquid faeces (Co 15 vs. Cr 50h) suggest that small particles did not simply move in parallel to fluids, but were retained selectively by being trapped in colonic digesta upon expulsion from caeca, with subsequent repeated retrograde transport into caeca with the next batch of urine. Given the absence of coprophagy in birds (in contrast to small mammalian herbivores), such a delay of small (microbial) particle escape from the caeca appears reasonable.

Digestive physiology, resting metabolism and methane production of captive Indian crested porcupine (<i>Hystrix indica</i>)

“…The marker excretion curves in two of the three animals of the present study contained secondary peaks, which have been considered to be indicators for caecotrophy (Clauss et al, 2007). It must be noted that theoretically, such peaks could also simply indicate a periodic release of caecum contents without caecotrophy as, for example, observed in birds (Frei et al, 2017). Ideally, therefore, passage studies in caecotroph species should simultaneously document behaviour by video surveillance, which was beyond the means of our current study.…”

Within trophic level shifts in collagen–carbonate stable carbon isotope spacing are propagated by diet and digestive physiology in large mammal herbivores

“…Additionally, because hens also produce CH 4 (Tsukahara & Ushida, 2000), physiologic effects of the different diets cannot be ruled out. The complicating factor in avian cecal fermentation is that in some species dietary fiber may not be the major substrate of fermentation and hence CH 4 production, but uric acid transported retrogradely from the cloaca into the caeca (Frei, Ortmann, Kreuzer, Hatt, & Clauss, 2017).…”

Are carnivore digestive separation mechanisms revealed on structure-rich diets?: Faecal inconsistency in dogs (Canis familiaris) fed day old chicks

“…Separation mechanisms in the digestive tract that selectively retain either fluids or particles have been described in many herbivorous species such as ruminants, lagomorphs, rodents and some birds [ 1 – 4 ]. Typically, the functional existence of these mechanisms is explained either with respect to a comparative delay or acceleration of plant fibre particles to, respectively, enhance their digestion or to rid the digestive tract of them quickly [ 5 ] or with respect to a washing of the particulate digesta by fluid in order to direct very fine particles, including microbes, in an aborad or orad direction [ 6 ].…”

“…In mammalian hindgut fermenters the first principle often occurs when the time-consuming process of fibre fermentation is accounted for by selectively retaining the small, easy-to-ferment plant fibre particles and excreting the larger, coarse, more difficult-to-ferment particles more rapidly from the hindgut [ 1 , 7 ]. Similarly, in some birds, this physical principle occurs with fluids and fine matter being retained in the caeca and coarse, large particles being excreted with the ordinary faeces [ 1 , 4 , 8 ]. Typically, this results in longer retention times for the fluid fraction and shorter retention times for larger particles [ 4 , 9 ].…”

“…Similarly, in some birds, this physical principle occurs with fluids and fine matter being retained in the caeca and coarse, large particles being excreted with the ordinary faeces [ 1 , 4 , 8 ]. Typically, this results in longer retention times for the fluid fraction and shorter retention times for larger particles [ 4 , 9 ]. In turkey ( Meleagris gallopavo ), this separation in particles leads to the presence of two faecal consistencies—solid vs liquid—with larger particles that tend to be excreted with solid excreta whereas the smaller ones are excreted in more liquid excreta [ 4 ] in which the protein level and microbial count is higher [ 8 ].…”