COMPOSITION OF THE MILK OF THE KOALA, PHASCOLARCTOS-CINEREUS, AN ARBOREAL FOLIVORE

The composition of milk from free-ranging koalas was examined as part of a study of the energetics of reproduction in the koala, an arboreal folivorous marsupial that displays a number of energetically conserva tive characteristics often associated with arboreality and folivory. K oala milk composition showed a number of deviations from the general m arsupial pattern that suggest koalas have adopted a lactational strate gy different from that of most other marsupials previously studied. Mi lk solids decreased at the time of exit of the young from the pouch, i n contrast with the solids content of the milk of most marsupials, whi ch rises at that time. Lipids provided that major source of milk energ y even in early to midlactation and did not rise at pouch exit, unlike lipid levels in other marsupials, which are low in early to midlactat ion and rise sharply at pouch exit to high levels in late lactation. T he carbohydrates of late-lactation koala milk contained mainly lactose and some oligosaccharides, but little or none of the monosaccharide f ound in the milk of many other marsupials. Koalas share most of these features with the common brushtail possum (Trichosurus vulpecula) and common ringtail possum (Pseudocheirus peregrinus), the only two other marsupial arboreal folivores in which milk composition has been studie d. This suggests that the koala's pattern of changes in milk compositi on may be common to marsupial arboreal folivores and may be associated with energetic limitations imposed directly by their folivorous diet or indirectly via selection for their long period of lactation and slo w weaning. However, koalas' milk was more concentrated that that of th e other two marsupial folivores, the importance of which, to the lacta tional strategy of the koala, can be resolved only by further study of milk production.