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Lactation Physiology (part 2)

فیزیولوژی تولید و ترشح شیر. Lactation Physiology (part 2). By: A. Riasi (PhD in Animal Nutrition & Physiology). Physiology of mammary gland during the dry period. During dry period the gland has three distinct functional states: The period of active involution

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Lactation Physiology (part 2)

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  1. فیزیولوژی تولید و ترشح شیر Lactation Physiology(part 2) By: A. Riasi (PhD in Animal Nutrition & Physiology)

  2. Physiology of mammary gland during the dry period • During dry period the gland has three distinct functional states: • The period of active involution • The period of steady state involution • The period of lactogenesis and colostrogenesis: • Regeneration and differentiation of secretory epithelial cells • Selective transport and accumulation of immunoglobulin • The onset of copious secretion

  3. Physiology of mammary gland during the dry period • The mammary gland undergoing transition at two stages: • At the beginning of the dry period • At the end of the dry period

  4. Physiology of mammary gland during the dry period • Reducing the length of the dry period of dairy cows may affect: • Postpartum health • Reproduction performance • Milk production

  5. Physiology of mammary gland during the dry period • Intra-alveolar pressure triggers the events of active involution: • The appearance of lysosomes in the secretory epithelial cells. • Macrophages enter the mammary tissue and secretion. • The rate of synthesis of major milk constituents decrease: • Fat • Casein • Lactose * • Citrate * • β-lactoglobulin • α-lactalbumin

  6. Physiology of mammary gland during the dry period • By 7 days involution, the concentration of serum proteins in mammary secretion is significantly elevated. • The permeability barriers are not totally destroyed and the mammary gland maintains a degree of control.

  7. Physiology of mammary gland during the dry period • The concentration of the iron biding protein lactoferrin (Lf) dramatically increase. • The major site of synthesis of the Lf found in bovine mammary secretions is thought to be the secretory epithelial cell. • Lf is a major protein in the secretion of the non-lactating mammary gland. • Lactoferrin is bacteriostatic by virtue of its ability to bind iron with great affinity.

  8. Development of the Mammary Gland (Mammogenesis) • Mammary gland has allometric and isometric growth • The development of mammary growth has five phases: • Fetal phase • Prepubertal phase • Postpubertal phase • Pregnancy • Lactation

  9. Development of the Mammary Gland (Mammogenesis)

  10. Development of the Mammary Gland (Mammogenesis)

  11. Development of the Mammary Gland (Mammogenesis) • Prepubertal mammary growth begins as isometric growth, and before puberty becomes allometric. • A large portion of mammary growth before puberty is an increase in: • Connective tissue • Ductal growth • Growth of the fat pad

  12. Development of the Mammary Gland (Mammogenesis) • Feed restricted heifers can have up to 30 percent larger mammary glands at puberty. • Studies have also shown that feeding high energy diets during the prepubertal period suppresses serum bovine somatotropin (bST) levels.

  13. Development of the Mammary Gland (Mammogenesis) • Through the first several estrous cycles after puberty, rapid mammary growth continues. • Most of the growth is lost through regression during the luteal phase of each estrous cycle. • Nutrition plays an important, though controversial, role in postpubertal mammary development.

  14. Development of the Mammary Gland (Mammogenesis) • Mammary growth is a continuous, exponential process from conception to parturition • The greatest increase occurs in mass of parenchymal tissue in late pregnancy. • The increasing udder size during the fifth and sixth months of pregnancy is due to: • The elongation of mammary ducts • The formation of alveoli • The reduction of identifiable fat cells in the fat pad

  15. Development of the Mammary Gland (Mammogenesis) • Mammary growth continues in early lactation. • Persistency of lactation (maintaining peak milk yield) depends on the continual survival of those milk-secreting cells. • In rats, increases in total mammary DNA was seen from parturition until weaning.

  16. Hormonal control of mammogenesis • The ovarian steroids are important for mammogenesis. • Ovarioectomy affect the parenchyma tissue of mammary gland. • The ovarian activity appears to mediate the actions of GH, specifically through changes in IGF-I.  • During pregnancy, Prl and PL provide support for mammogenesis in some species.

  17. Hormonal control of mammogenesis • Mammogenesis depends not only on hormonal concentration but also on: • Receptor availability within the mammary tissue • The presence of transport proteins and intracellular lipids that are capable of making steroids unavailable to the tissues.

  18. Hormonal control of mammogenesis • Several other hormones play a permissive and supportive role in mammary growth: • Placental lactogens • Adrenal gland hormones • Thyroid hormones • Relaxin • Parathyroid hormone • Effect of parathyroid hormone-related protein (PTHrP)

  19. Hormonal control of mammogenesis • Other factors that may affect mammogensis: • Insulin-like growth factors (IGF) • Epidermal cell factors (ECF) • Transforming growth factors (TGF) • Fibroblast growth factors (FGFs)

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