Prepubertal Development

Prepubertal mammary development is important to the milk-producing ability of an animal, as either excessive energy intake or under-nutrition may impair future milk yield of dairy animals.[2] In dairy cattle, the amount of mammary parenchyma increases nearly 100fold between birth and puberty. Much of the parenchymal growth involves penetration of the unpopulated mammary fat pad. In the murine mammary gland, structures at the distal extremity of mammary ducts, known as the terminal end buds (TEB), are responsible for this parenchymal invasion. In ruminants, more arborescent structures known as terminal ductal units (TDU) are responsible for parenchymal development.[3] Proliferation of epithelial cells occurs throughout the TDU, with the greatest rates of growth at the periphery. Regardless of the specific architectural features of development, no true alveolar development occurs prepubertally. Instead, there is a progressive increase in the amount and size of ductal structures upon which alveoli will develop during pregnancy. In ruminants, ductal elongation does not reach the limits of the mammary fat pad by the onset of puberty. The teat and gland cisterns developed in concert with the rest of the milk-conducting and-storage structures in the gland. Mice lack a gland cistern and only develop relatively large milk ducts.

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