title: 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.
authors.affiliation: Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland.
authors.forename: Samuel
authors.initials: S
authors.lastname: Frei
authors.affiliation: Leibniz Institute for Zoo and Wildlife Research (IZW) Berlin, Alfred-Kowalke-Str. 17, 10315 Berlin, Germany.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Ortmann
authors.affiliation: ETH Zurich, Institute of Agricultural Sciences, Universitätsstr. 2, 8092 Zurich, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Kreuzer
authors.affiliation: Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland.
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Hatt
authors.affiliation: Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland. Electronic address: mclauss@vetclinics.uzh.ch.
authors.forename: Marcus
authors.initials: M
authors.lastname: Clauss
mesh_terms: D000818:Animals; D002432:Cecum / Q000502:physiology*; D004063:Digestion / Q000502:physiology*; D005777:Geese / Q000502:physiology*; D014422:Turkeys / Q000502:physiology*
keywords: Caecum; Colonic separation mechanism; Digesta passage; Digestion; Gut capacity; Intake