MILK-COMPOSITION IN THE COMMON RINGTAIL POSSUM, PSEUDOCHEIRUS-PEREGRINUS (PETAURIDAE, MARSUPIALIA)

Milk samples were collected from captive common ringtail possums, Pseudocheirus peregrinus, throughout lactation and from free-living animals during phase 3 of lactation (weeks 15-30 post partum). Both field and captive animals lactated for approximately 30 weeks. In comparison with the milks of other marsupial species, ringtail possum milk was relatively dilute and low in lipid. During phase 2 of lactation (up to week 14) solids represented around 16% (w/w), comprising mostly carbohydrate and protein, increasing to 25% (w/w) at the onset of pouch emergence. During the period of pouch vacation (weeks 15-18) the carbohydrate concentration declined and protein and lipid concentrations peaked. Sodium and potassium concentrations throughout lactation were around 25 mm and 22 mm respectively. Calcium and magnesium levels were around 1.8 g per L and 131 mg per L respectively. Milk carbohydrates consisted mainly of oligosaccharides during phase 2 of lactation and these were replaced by the disaccharide lactose during phase 3 of lactation. The pattern of change in the composition of ringtail possum milk during phase 2 was similar to that shown by those of other marsupials, but during phase 3 the milk had higher levels of carbohydrate and lower levels of lipid than that of other marsupials. Differences in the composition of milk from free-living and captive animals suggest that diet composition may affect the concentration of milk protein and milk fat within a species.