title: Methane output of tortoises: its contribution to energy loss related to herbivore body mass.
abstract: An increase in body mass (M) is traditionally considered advantageous for herbivores in terms of digestive efficiency. However, recently increasing methane losses with increasing M were described in mammals. To test this pattern in non-mammal herbivores, we conducted feeding trails with 24 tortoises of various species (M range 0.52-180 kg) fed a diet of grass hay ad libitum and salad. Mean daily dry matter and gross energy intake measured over 30 consecutive days scaled to M(0.75 (95%CI 0.64-0.87)) and M(0.77 (95%CI 0.66-0.88)), respectively. Methane production was measured over two consecutive days in respiration chambers and scaled to M(1.03 (95%CI 0.84-1.22)). When expressed as energy loss per gross energy intake, methane losses scaled to 0.70 (95%CI 0.47-1.05) M(0.29 (95%CI 0.14-0.45)). This scaling overlaps in its confidence intervals to that calculated for nonruminant mammals 0.79 (95%CI 0.63-0.99) M(0.15 (95%CI 0.09-0.20)), but is lower than that for ruminants. The similarity between nonruminant mammals and tortoises suggest a common evolution of the gut fauna in ectotherms and endotherms, and that the increase in energetic losses due to methane production with increasing body mass is a general allometric principle in herbivores. These findings add evidence to the view that large body size itself does not necessarily convey a digestive advantage.
authors.affiliation: Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
authors.forename: Ragna
authors.initials: R
authors.lastname: Franz
authors.forename: Carla R
authors.initials: CR
authors.lastname: Soliva
authors.forename: Michael
authors.initials: M
authors.lastname: Kreuzer
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Hatt
authors.forename: Samuel
authors.initials: S
authors.lastname: Furrer
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hummel
authors.forename: Marcus
authors.initials: M
authors.lastname: Clauss
mesh_terms: D000663:Amphibians / Q000378:metabolism*; D000818:Animals; D049628:Body Size / Q000502:physiology; D001835:Body Weight / Q000502:physiology*; D002473:Cell Wall / Q000378:metabolism; D004063:Digestion / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology*; D008697:Methane / Q000096:biosynthesis*; D012418:Ruminants / Q000378:metabolism
chemical_list: D008697:Methane