title: Decreasing methane yield with increasing food intake keeps daily methane emissions constant in two foregut fermenting marsupials, the western grey kangaroo and red kangaroo.
abstract: Fundamental differences in methane (CH4) production between macropods (kangaroos) and ruminants have been suggested and linked to differences in the composition of the forestomach microbiome. Using six western grey kangaroos (Macropus fuliginosus) and four red kangaroos (Macropus rufus), we measured daily absolute CH4 production in vivo as well as CH4 yield (CH4 per unit of intake of dry matter, gross energy or digestible fibre) by open-circuit respirometry. Two food intake levels were tested using a chopped lucerne hay (alfalfa) diet. Body mass-specific absolute CH4 production resembled values previously reported in wallabies and non-ruminant herbivores such as horses, and did not differ with food intake level, although there was no concomitant proportionate decrease in fibre digestibility with higher food intake. In contrast, CH4 yield decreased with increasing intake, and was intermediate between values reported for ruminants and non-ruminant herbivores. These results correspond to those in ruminants and other non-ruminant species where increased intake (and hence a shorter digesta retention in the gut) leads to a lower CH4 yield. We hypothesize that rather than harbouring a fundamentally different microbiome in their foregut, the microbiome of macropods is in a particular metabolic state more tuned towards growth (i.e. biomass production) rather than CH4 production. This is due to the short digesta retention time in macropods and the known distinct 'digesta washing' in the gut of macropods, where fluids move faster than particles and hence most likely wash out microbes from the forestomach. Although our data suggest that kangaroos only produce about 27% of the body mass-specific volume of CH4 of ruminants, it remains to be modelled with species-specific growth rates and production conditions whether or not significantly lower CH4 amounts are emitted per kg of meat in kangaroo than in beef or mutton production.
authors.affiliation: Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, 8057 Zurich, Switzerland Centre for Sustainable Ecosystems Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.
authors.forename: Catharina
authors.initials: C
authors.lastname: Vendl
authors.affiliation: Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, 8057 Zurich, Switzerland.
authors.forename: Marcus
authors.initials: M
authors.lastname: Clauss
authors.affiliation: Centre for Sustainable Ecosystems Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.
authors.forename: Mathew
authors.initials: M
authors.lastname: Stewart
authors.affiliation: Fowlers Gap Arid Zone Research Station, School of Biological, Earth and Environmental Sciences, University of New South Wales, Fowlers Gap, Broken Hill, NSW 2880, Australia.
authors.forename: Keith
authors.initials: K
authors.lastname: Leggett
authors.affiliation: Department of Animal Sciences, Ruminant Nutrition, University of Göttingen, 37077 Göttingen, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hummel
authors.affiliation: ETH Zurich, Institute of Agricultural Sciences, 8092 Zurich, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Kreuzer
authors.affiliation: Centre for Sustainable Ecosystems Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia Fowlers Gap Arid Zone Research Station, School of Biological, Earth and Environmental Sciences, University of New South Wales, Fowlers Gap, Broken Hill, NSW 2880, Australia amunn@uow.edu.au.
authors.forename: Adam
authors.initials: A
authors.lastname: Munn
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D004043:Dietary Fiber; D004063:Digestion; D004064:Digestive System / Q000378:metabolism*; D004435:Eating; D007614:Macropodidae / Q000378:metabolism*; D000455:Medicago sativa; D008697:Methane / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D004043:Dietary Fiber; D008697:Methane
keywords: CH4; Digesta washing; Digestion; Fermentation; Forestomach; Macropod; Methanogenesis