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Digestion, nutrition & metabolism

Composition of preferred and rejected Eucalyptus browse offered to captive koalas, Phascolarctos cinereus (Marsupialia)

Ullrey, DE, Robinson, PT & Whetter, PA 1981, Australian Journal of Zoology, vol. 29, pp. 839-846.

Browse from eleven species of Eucalyptus tree shoots or mature limbs were offered to captive koalas at the San Diego Zoo, California and subsequently sorted into ‘preferred’ or ‘rejected’ species. Analyses revealed that, compared to rejected browse, preferred browse contained significantly higher crude protein, remaining proximate fraction, potassium and phosphorus concentrations and significantly lower neutral detergent fibre, acid detergent fibre, ether extract, calcium, iron, selenium, permanganate lignin, and gross energy concentrations.

  Koalas exclusively feed on the leaves of Eucalyptus trees. Very few of the 600 described Eucalyptus species are able to provide all of the koala’s nutritional needs. It is therefore essential that captive koalas are provided with browse from the appropriate Eucalyptus species. Preferred and rejected browse species in this study had significantly different concentrations of several nutrients, as described above. When a large amount of browse is presented to koalas, they select the younger, more tender leaves, as these leaves have relatively higher concentrations of important nutrients including protein and phosphorus. As they contain less fibre and lignin, these leaves are likely to be more digestible too. If captive koalas were forced to subsist on the browse they rejected here, the amount of dietary protein and phosphorus consumed would be below that considered minimally essential for domestic sheep and horses. It appears, therefore, that koalas may intentionally select the more nutritional Eucalyptus species for their consumption.

  The precise nutritional requirements of koalas are yet to be determined, and this is a field which requires further research. As browse accepted by captive koalas varies considerably in concentrations of important nutrients such as sodium, zinc and copper, it is recommended that captive koalas should be provided with foliage of a variety of species of Eucalyptus to ensure a natural and nutritionally balanced diet.


Summarised by Alexander Hendry


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