Marsupialia

Marsupial young are both very small (0.004 0.93 g) and very altricial (immature) at birth. Survival after birth depends on successful attachment to a nipple, which swells in size to fill the mouth, forming a seal. The nipples and attached young may be within a pouch, as in kangaroos and wallabies, but many pouchless species (including opossums) carry their young dangling from the nipples when traveling. Both the nipples and mammary glands increase in size as the young mature, and the milk, which was quite dilute at birth, becomes increasingly rich in fat, protein, and sugars, especially oligosaccharides. An important developmental milestone is the time of teat detachment, which initiates a period of rapid change in milk composition as fat and protein increase but sugars decline markedly.[9] Some marsupials, such as kangaroos and wallabies, give birth while an older young is still suckling. The neonate attaches to a nipple that produces dilute secretion, while the older ''joey'' continues to ingest late lactation milk of very different composition.

Pregnancy And Childbirth

Pregnancy And Childbirth

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