The physiology of marsupials is well described by
Tyndale-Biscoe (2005). Marsupials have a lower metabolic
rate than eutherians. However, they require higher
dosages of injectable anesthetics than eutherians of
similar size. For example, three times as much xylazine/
ketamine is required to immobilize a possum than a cat
of similar size. The reasons are unknown.
Marsupials have a lower body temperature than
eutherians. Instead of a separate anus and urogenital
opening they combine the two into a single cloaca. To
effectively measure a marsupial’s temperature the thermometer
is inserted in the dorsal part of the cloaca,
leading to the rectum. Thermoregulatory ability is slow
to develop. For example, kowaris (Dasyuroides byrnii)
cannot thermoregulate until about 100 days after birth.
Consequently, it is important to provide supplemental
heat if young animals, particularly unfurred, are anesthetised.
Marsupials combat cold by shivering. They do
not have brown adipose tissue, which is used by some
eutherians to generate heat. They cope with excessive
heat by panting and licking. Kangaroos, in particular,
will lick their forelegs to keep cool.