Presentation on theme: "Hormones Control of Lactogenesis and Galactopoiesis."— Presentation transcript:
Hormones Control of Lactogenesis and Galactopoiesis
Hormone Levels at Calving
Blocking Prolactin Secretion
Prolactin Effects on Lactation
Effect of Prolactin Secretion on Milk Yield
In Vitro Lactogenesis Control contains insulin and T3.
Progesterone on Lactogenesis Control contains insulin,cortisol and T3.
GH on Lactogenesis
Hormone Priming on Lactogenesis From:Sheffield, l.G. and C.W. Welsch, J. Dairy Sci, 71:75-83, 1988.
Extracellular Matrix on Lactogenesis
Model of Lactogenesis
Hormonal Regulation of Lactation
Effects of Estrogen and Progesterone on Lactation
Hormonal Maintenance of Lactation
Hormones and the Maintenence of Lactation
Insulin and Growth Hormone Throughout Lactation
Growth Hormone Levels in Cattle Selected for Higher Milk Production vs. Control Cattle
Prolactin Throughout Lactation
Insulin, Growth Hormone and Cortisol Through Lactation
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.
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.
Prolactin Concentration at Milking
Alveolus Stained to Show Myoepithelium Myoepithelial Cell
Milk Letdown Reflex
Milk Letdown Alveolar Contraction
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.
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