Hormones Control of Lactogenesis and Galactopoiesis
Slide 2
Hormone Levels at Calving
Slide 3
Blocking Prolactin Secretion
Slide 4
Prolactin Effects on Lactation
Slide 5
Effect of Prolactin Secretion on Milk Yield
Slide 6
In Vitro Lactogenesis Control contains insulin and T3.
Slide 7
Progesterone on Lactogenesis Control contains insulin,cortisol
and T3.
Slide 8
GH on Lactogenesis
Slide 9
Hormone Priming on Lactogenesis From:Sheffield, l.G. and C.W.
Welsch, J. Dairy Sci, 71:75-83, 1988.
Slide 10
Extracellular Matrix on Lactogenesis
Slide 11
Model of Lactogenesis
Slide 12
Hormonal Regulation of Lactation
Slide 13
Effects of Estrogen and Progesterone on Lactation
Slide 14
Hormonal Maintenance of Lactation
Slide 15
Hormones and the Maintenence of Lactation
Slide 16
Insulin and Growth Hormone Throughout Lactation
Slide 17
Growth Hormone Levels in Cattle Selected for Higher Milk
Production vs. Control Cattle
Slide 18
Prolactin Throughout Lactation
Slide 19
Insulin, Growth Hormone and Cortisol Through Lactation
Slide 20
Oxytocin Oxytocin is a 9 amino acid long peptide. The amino
acid structure of oxytocin is: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly
It has a molecular mass of 1007 daltons. Oxytocin has a disulfide
bond between the two cysteines. Reduction of the disulfide bond
inactivates oxytocin. One IU (international Unit) is approximately
2 micrograms of pure peptide.
Slide 21
Oxytocin Synthesis Oxytocin is synthized in the hypothalamus in
specific nuclei, the paraventricular nucleus and the supraoptic
nucleus in the hypothalamus. [A cluster of nerve cells in the brain
is often called a nucleus. This is different from the nucleus of a
single cell.] Neurons in these hypothalamic nuclei synthesize the
oxytocin precursor and package it into vesicles. Oxytocin is
initially synthesized as a large molecular weight precursor which
also consists of the oxytocin-carrier peptide neurophysin. The
precursor is proteolytically cleaved in the neuron in the oxytocin-
containing vesicle to yield oxytocin bound to neurophysin. The
oxytocin- neurophysin complex is the intracellular storage form of
oxytocin. The oxytocin-containing vesicles are transported from the
cell body (which is in the hypothalamus), down the axons to the
neuron endings in the posterior pituitary. This is called the
hypothalamo-neurohypophysial tract. The oxytocin-neurophysin
complex is stored in neurosecretory granules called herring bodies
in the axon ending.
Slide 22
Pituitary Gland
Slide 23
Slide 24
Prolactin Concentration at Milking
Slide 25
Alveolus Stained to Show Myoepithelium Myoepithelial Cell
Slide 26
Milk Letdown Reflex
Slide 27
Milk Letdown Alveolar Contraction
Slide 28
Oxytocin Release and Half-Life It is estimated that the bovine
pituitary has about 800 micrograms of oxytocin. This is about 40X
what is in the blood under resting conditions. Only about 1/3 of
pituitary oxytocin is released at a milking. Oxytocin receptors on
myoepithelial cells can respond to very low levels of oxytocin.
Oxytocin has a short half-life in the blood = 0.55 to 3.6 min. This
means that the removal of milk by machine or by nursing must be
closely timed with stimulation of the teats.
Slide 29
Factors Modifying Milk Letdown Autonomic nervous system Stress
gives epinephrine release Inhibits oxytocin release Inhibits
myoepithelial cell contraction Inhibits blood flow to udder
Conditioned reflex Letdown in response to sights, sounds associated
with milking
Residual Milk Left in udder after normal milking About 10% of
milk Can remove with oxytocin
Slide 38
Phase Separation and Residual Milk
Slide 39
Removing Residual Milk Oxytocin injections Expensive Not
approved use Machine stripping High incidence of liner slips
Increases mastitis risk Udder massage Second oxytocin release.
