Hormones Control of Lactogenesis and Galactopoiesis
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- Slide 1
- Hormones Control of Lactogenesis and Galactopoiesis
- Slide 2
- Hormone Levels at Calving
- Slide 3
- Blocking Prolactin Secretion
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- Prolactin Effects on Lactation
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- Effect of Prolactin Secretion on Milk Yield
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- In Vitro Lactogenesis Control contains insulin and T3.
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- Progesterone on Lactogenesis Control contains insulin,cortisol
and T3.
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- GH on Lactogenesis
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- 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
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- Model of Lactogenesis
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- Hormonal Regulation of Lactation
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- Effects of Estrogen and Progesterone on Lactation
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- Hormonal Maintenance of Lactation
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- Hormones and the Maintenence of Lactation
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- Insulin and Growth Hormone Throughout Lactation
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- Growth Hormone Levels in Cattle Selected for Higher Milk
Production vs. Control Cattle
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- Prolactin Throughout Lactation
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- Insulin, Growth Hormone and Cortisol Through Lactation
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- 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.
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- Pituitary Gland
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- Prolactin Concentration at Milking
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- Alveolus Stained to Show Myoepithelium Myoepithelial Cell
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- Milk Letdown Reflex
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- Milk Letdown Alveolar Contraction
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- 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
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- Interesting Stimulation of Milk Letdown
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- Adrenal Medulla Myoepithelium Udder VasculaturePosterior
Pituitary Adrenal Medulla Epinephrine Ihnibits oxytocin release
Inhibits Blood Flow Inhibits Contraction
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- Milking Apparatus
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- Teat Cup Structure
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- Milking Stimulus and Oxytocin Release
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- Residual Milk Left in udder after normal milking About 10% of
milk Can remove with oxytocin
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- Phase Separation and Residual Milk
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- Removing Residual Milk Oxytocin injections Expensive Not
approved use Machine stripping High incidence of liner slips
Increases mastitis risk Udder massage Second oxytocin release.
- Slide 40
- Udder Pressure and Milk Secretion
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- Milk Letdown and Mammary Pressure
- Slide 42
- Effect of Exogenous Oxytocin on Milk Yield