1. Chapter 4 Physiology of Milk Synthesis

17. 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

18. Epithelial Cell Mitochondria E.R. Blood Vessel Nucleus Fat Droplet Fat Droplet migrating Golgi BodyLysosome Lumen of alveolus

19. Epithelial Cell Mitochondria E.R. Blood Vessel Nucleus Fat Droplet Fat Droplet migrating Golgi BodyLysosome Lumen of alveolus

20. Epithelial Cell Mitochondria E.R. Blood Vessel Nucleus Fat Droplet Fat Droplet migrating Golgi BodyLysosome Lumen of alveolus Cell pinches off

21. Epithelial Cell Mitochondria E.R. Blood Vessel Nucleus Fat Droplet Fat Droplet migrating Golgi BodyLysosome Lumen of alveolus Cell pinches off

22. 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 4.5 2.3 1.3 2.7 3.0 10.6 28.2 12.6

23. Major Fatty Acids (wt%) of Bovine Milk Monounsaturated Fatty Acids 16:1 18:1 Palmitoleic acid Oleic acid 1.6 21.4

24. Major Fatty Acids (wt%) of Bovine Milk Polyunsaturated Fatty Acids 18:2 18:3 Linoleic acid Linolenic acid 2.9 0.3

26. Effect of hydrogenation by rumen microorganisms on dietary lipids Wt% of Fatty Acids Fatty acidDietAbomasal digesta 16:0 18:0 18:2 18:3 26 3 17 31 29 45 4 6

27. 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

29. 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

36. 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

42. Udder Pressure & Secretion Rate Secretion Rate (kg/hr) ( ____ ) 1.5 1.0 0.5 0

43. Secretion Rate Influence of udder pressure Milking intervals –12 hour vs. other –2X vs. 3X –young vs. old cows

45. Yield and Milking Frequency (Erdman & Varner, 1995 JDS) ItemMilk yieldFat%Protein % # studies40184 2X42.93.653.10 3X50.63.513.05 # studies433 2X54.64.713.49 4X64.54.533.44

46. Milk Let Down Refractory period to oxytocin? Adrenaline interferes

47. Milk Ejection Stimulus nerves P.P. brain

48. Milk Ejection nerves P.P.

49. Milk Ejection P.P.

50. Milk Ejection Oxytocin Jugular vein Abdominal aorta heart

51. Milk Ejection Oxytocin

52. Milk Ejection Oxytocin

53. Milk Ejection

56. Contraction of an Alveolus arteriole venuole Oxytocin Lumen Duct Myoepithelial Cell

57. Contraction of an Alveolus Oxytocin Myoepithelial Cell contracts

58. Contraction of an Alveolus Releases milk into duct system

59. Contraction of an Alveolus Myoepithelial cell relaxes

60. Contraction of an Alveolus

64. Milk Fat % as Milking Progresses

65. Milk Fat % & Exercise

67. Biosynthesis of Milk components Precursors from blood One liter of milk requires 500 L of blood Fat biosynthesis Protein biosynthesis Lactose biosynthesis

68. 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)

70. Major Fatty Acids (wt%) of Bovine Milk Polyunsaturated Fatty Acids 18:2 18:3 Linoleic acid Linolenic acid 2.9 0.3