THE INITIATION AND MAINTENANCE OF LACTATION IN THE MARSUPIAL, TRICHOSURUS VULPECULA

Abstract

SUMMARY The mammary glands of the marsupial Trichosurus vulpecula (the brush possum) showed a cycle of development and regression correlated with the oestrous cycle. Mammary glands of pregnant females were not significantly heavier than those of non-pregnant females at comparable times after oestrus. There were no clear differences in histology between mammary glands of mated and non-mated females at the same number of days after oestrus until the 17th day. At this time the mammary glands of three non-mated females were clearly different from the glands of three post-partum females. Lactation was initiated in six out of eight non-mated females, including one virgin female, by transferring newborn young, which attached themselves to teats, to their pouches. Of the six transferred young which attached all, except one, lived and showed normal growth. The rate of regression of previously suckled mammary glands was slower in lactating than in non-lactating females. No clear evidence was obtained of hypertrophy of the non-suckled mammary gland following the attachment of a single young to the teat of the alternate mammary gland. However, the micro-anatomy of the non-suckled gland at 8 days after the onset of lactation suggested that milk may have distended the alveoli. These observations are discussed in relation to the control of lactation in the female marsupial. It is suggested that, in marsupials, the hormones circulating during the oestrous cycle cause full mammary development and that the suckling stimulus of the newborn young is sufficient to initiate lactation. The yolk-sac placenta of the brush possum apparently plays no essential part in mammary gland development. Otherwise the pattern of lactation in the brush possum does not appear to differ from that of eutherian mammals.