Digestion and metabolism of a natural foliar diet (Eucalyptus punctata) by an arboreal marsupial, the koala (Phascolarctos cinereus)

Abstract

Digestion and energy metabolism in an arboreal marsupial, the koala Phascolarctos cinereus, fed mature foliage from a common food tree, the grey gum Eucalyptus punctata, were investigated. Six feeding (balance) experiments, at various times of year, and one slaughter experiment were performed and average daily oxygen consumption was measured. The average apparent digestibilities of dietary constituents were: dry matter 54%; total cell-contents 69%; available carbohydrate 92%; crude lipid 43%; total nitrogen 45%; total phenolics 91%; total cell walls 25%; hemicellulose 24%; acid-detergent fibre 25%; cellulose 31%; lignin 19%. Average digestible and metabolizable energy intakes were 0.50 and 0.43 MJ kg-0.75 d-1 respectively of which only 0.28 MJ kg-0.75 d-1 was expended in oxidative metabolism. The digestible energy intake required for maintenance was estimated to be 0.33 MJ kg-0.75 d-1, which is lower than that of eutherian and of other marsupial herbivores. The principal sources of metabolizable energy were non-structural carbohydrate and lipid. It is postulated that the ability of koalas to utilize Eucalyptus foliage as a sole source of nutrients is facilitated by their low requirement for energy and their ability to maximize intake of non cell-wall constituents. E. punctata foliage has a high digestible energy content compared with the foliage of many other trees and this may be a factor in its selection by koalas. Show more