Chapter 4 Physiology of Milk Synthesis
Basal membraneERmembraneLuminalmembrane LPL FAS ACC de novo FA synthesis (C 4 -C 16 ) TAG synthesis Glucose SFA (C 16 -C 18 ) SynthesisSecretion Acetate ßHBA TAG Glucose CirculationTranslocation UFA FABP NEFA + Glycerol MFGM Glycerol -P Milk Fat Synthesis
Epithelial Cell Mitochondria E.R. Blood Vessel Nucleus Fat Droplet Fat Droplet migrating Golgi BodyLysosome Lumen of alveolus
Epithelial Cell Mitochondria E.R. Blood Vessel Nucleus Fat Droplet Fat Droplet migrating Golgi BodyLysosome Lumen of alveolus
Epithelial Cell Mitochondria E.R. Blood Vessel Nucleus Fat Droplet Fat Droplet migrating Golgi BodyLysosome Lumen of alveolus Cell pinches off
Epithelial Cell Mitochondria E.R. Blood Vessel Nucleus Fat Droplet Fat Droplet migrating Golgi BodyLysosome Lumen of alveolus Cell pinches off
Major Fatty Acids (wt%) of Bovine Milk Saturated Fatty Acids 4:0 6:0 8:0 10:0 12:0 14:0 16:0 18:0 Butyric acid Hexanoic acid Octanoic acid Decanoic acid Lauric acid Myristic acid Palmitic acid Stearic acid
Major Fatty Acids (wt%) of Bovine Milk Monounsaturated Fatty Acids 16:1 18:1 Palmitoleic acid Oleic acid
Major Fatty Acids (wt%) of Bovine Milk Polyunsaturated Fatty Acids 18:2 18:3 Linoleic acid Linolenic acid
Effect of hydrogenation by rumen microorganisms on dietary lipids Wt% of Fatty Acids Fatty acidDietAbomasal digesta 16:0 18:0 18:2 18:
linoleicacid ( cis -9, cis -12 C 18:2 ) conjugatedlinoleicacid ( cis -9, trans -11 C 18:2 ) conjugatedlinoleicacid trans -10, cis -12 C 18:2 trans -10 C 18:1 linoleicacid ( cis -9, cis -12 C 18:2 ) ( cis -9, trans - vaccenic acid (trans-11 C 18:1 ) stearic acid (C 18:0 ) conjugatedlinoleicacid trans -10, cis - trans -10 C 18:1 Changes in rumen conditions that lead to milk fat depression
Milk Fat Concentration Most variable component of milk Increased during periods of energy deficit Decreased when fed diets containing unsaturated fatty acids (most grains) and low effective fiber (change rumen conditions) – Milk fat depression (<2.8% fat) Fatty acid changes also occur
Milk Protein Concentration Not too variable Changes related to dietary energy intake, not dietary protein – little effect of dietary fat on milk protein concentration unless perturb normal rumen function – fermentable carbohydrate intake is the key! Maximize VFA and microbial protein production
Udder Pressure & Secretion Rate Secretion Rate (kg/hr) ( ____ )
Secretion Rate Influence of udder pressure Milking intervals –12 hour vs. other –2X vs. 3X –young vs. old cows
Yield and Milking Frequency (Erdman & Varner, 1995 JDS) ItemMilk yieldFat%Protein % # studies X X # studies433 2X X
Milk Let Down Refractory period to oxytocin? Adrenaline interferes
Milk Ejection Stimulus nerves P.P. brain
Milk Ejection nerves P.P.
Milk Ejection P.P.
Milk Ejection Oxytocin Jugular vein Abdominal aorta heart
Milk Ejection Oxytocin
Milk Ejection Oxytocin
Milk Ejection
Contraction of an Alveolus arteriole venuole Oxytocin Lumen Duct Myoepithelial Cell
Contraction of an Alveolus Oxytocin Myoepithelial Cell contracts
Contraction of an Alveolus Releases milk into duct system
Contraction of an Alveolus Myoepithelial cell relaxes
Contraction of an Alveolus
Milk Fat % as Milking Progresses
Milk Fat % & Exercise
Biosynthesis of Milk components Precursors from blood One liter of milk requires 500 L of blood Fat biosynthesis Protein biosynthesis Lactose biosynthesis
Milk Fat biosynthesis Requires fatty acids and glycerol Two sources of fatty acids: 1- blood lipids (dietary lipids & adipose tissue) 2- De novo synthesis (within the MG)
Major Fatty Acids (wt%) of Bovine Milk Polyunsaturated Fatty Acids 18:2 18:3 Linoleic acid Linolenic acid