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Lactation in the marsupial Macropus eugenii

Findlay, Leigh (1982) Lactation in the marsupial Macropus eugenii. PhD thesis, Murdoch University.

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Three aspects of lactation were investigated in the tammar wallaby (Maoropus eugenii): the development of the mammary glands; the hormonal control of lactogenesis; and the relationship between milk conposition, the sucking stimulus and pouch young growth.

The mammary glands of the tammar wallaby differentiate during pregnancy by proliferation of the epithelial cells to form alveoli. At parturition all four glands begin to lactate, but only the sucked gland grows and develops, showing progressive reduction in stromal volume and increased alveolar diameters. Simultaneously the three non-sucked glands regress to a quiescent state. The cellular processes of glandular development, regression and involution appear similar to those in other marsupials, monotremes and eutherians, but the temporal course of these events differs among these groups of mammals.

Mammary gland lactose concentrations in pregnant tammar wallabies remained low at 115 ± 24 µg/g wet weight of tissue (mean ± SEM) until immediately before parturition, then increased to 1274 ± 262 µg/g after birth. This rapid increase thus provides a useful index of synthetic activity in the mammary glands. The glands of some non-pregnant animals also showed transient synthetic activity around oestrus. Removal of the corpus luteum on Day 18 of pregnancy or the oestrous cycle (to effect premature progesterone withdrawal) resulted in an elevation of mammary lactose concentrations. However, as lactose concentrations were similarly raised in sham-operated animals in which no progesterone withdrawal occurred, it appears that other prolactational hormones may be important for lactogenesis in tammar wallabies. Plasma cortisol concentrations were also measured in some of these animals, but showed no consistent relationships with the raised lactose concentrations.

Local injection of prolactin into the mammary glands of wallabies on Day 15 after removal of the pouch young indicated that prolactin can exert a lactogenic effect, as assessed by the histological appearance of the tissue four days later.

Temporary depression of triglyceride and protein concentrations in the milk occurred when a constant age of the pouch young sucking the mammary glands was maintained by transferring 35-day old pouch young to the teats at fortnightly intervals. No effect on the milk protein concentration was detected when pouch young older or younger than the stage of lactation of the glands were transferred between foster mothers. However, the growth rates of these pouch young were affected and this was probably a function of both the different quantity and quality of the milk ingested. The normal changes in the milk composition appeared to be an intrinsic characteristic of the glands and occurred regardless of alterations in the local stimuli produced by the sucking young.

These features of lactation in the tammar wallaby are probably representative of lactation in all macropodid marsupials, and possibly other marsupials. While many fundamental similarities exist between lactation in all mammals, differences and specializations are found both between and within the three major groups, and these differences can be related to the ecology and reproductive patterns of the species.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Environmental and Life Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Renfree, Marilyn
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