Jørgen Madsen (KU-LIFE), Mads Bertelsen

The claimed low production of methane by kangaroos and marsupials in general has been questioned due to few measurements (Wilson and Edwards, 2008). The extent of their methane production is of interest both from the point of view of discussing meat production on marsupials and as a basis for developing methods to reduce the methane production from ruminants. In the present experiment, the methane production of eight Bennett’s wallaby (Macropus rufogriseus) of which four were fed two different diets was measured in an open circuit respiration chamber. These results were compared to a newly developed, inexpensive and simple method that does not influence the animal’s behaviour, where the ratio between methane and carbon dioxide is measured and used together with the calculated carbon dioxide to quantify the methane production.. The experiment shows that the Wallabies produce methane. The amount of methane measured on these 16 kg wallabies was between 1.6 and 2.2 litres /day equivalent to 1.6% and 2.2% of the gross energy intake and 0.22 litre/kg^0.75, which are between 1/4, and 1/3 of what can be expected from ruminants fed the same diet. Based on the uneven release with time of CH₄ in the wallabies it is most likely that the CH₄ is excreted through flatulence and not through the breath as in ruminants. The experiments also show that a reasonably accurate determination of the methane production of a group of animals can be obtained by simply measuring the CH₄/CO₂ ratio over a limited time span, and that this may represent the real situation better than measurements in a respiration chamber. It is found that the CH₄/CO₂ ratio in itself represents a reasonable prediction of the proportion of feed gross energy that is lost as methane.