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Chapter 4. Physiology of Milk Synthesis. FABP. MFGM. ACC. Milk Fat Synthesis. Circulation. Synthesis. Translocation. Secretion. UFA. TAG. LPL. NEFA. TAG. SFA. (C. -. C. ). 16. 18. +. synthesis. Glycerol. Glycerol. Glycerol. -. P. Glucose. Glucose. Acetate. de novo.

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Chapter 4

Chapter 4

Physiology of Milk Synthesis


FABP

MFGM

ACC

Milk Fat Synthesis

Circulation

Synthesis

Translocation

Secretion

UFA

TAG

LPL

NEFA

TAG

SFA

(C

-

C

)

16

18

+

synthesis

Glycerol

Glycerol

Glycerol

-

P

Glucose

Glucose

Acetate

de novo

FA synthesis

(C

-

C

)

4

16

ßHBA

FAS

membrane

ER

membrane

Luminal

membrane

Basal


Epithelial Cell

Lumen of alveolus

Fat Droplet

Fat Droplet migrating

Golgi Body

Lysosome

Nucleus

Mitochondria

Mitochondria

E.R.

Blood Vessel


Epithelial Cell

Lumen of alveolus

Fat Droplet

Fat Droplet migrating

Golgi Body

Lysosome

Nucleus

Mitochondria

Mitochondria

E.R.

Blood Vessel


Epithelial Cell

Lumen of alveolus

Fat Droplet

Cell pinches off

Fat Droplet migrating

Golgi Body

Lysosome

Nucleus

Mitochondria

Mitochondria

E.R.

Blood Vessel


Epithelial Cell

Lumen of alveolus

Fat Droplet

Cell pinches off

Fat Droplet migrating

Golgi Body

Lysosome

Nucleus

Mitochondria

Mitochondria

E.R.

Blood Vessel





Changes in rumen conditions

that lead to milk fat depression

linoleic

linoleic

acid

acid

(

(

-

-

9,

9,

-

-

12 C

12 C

)

)

cis

cis

cis

cis

18:2

18:2

conjugated

conjugated

linoleic

linoleic

acid

acid

conjugated

linoleic

acid

-

-

10,

10,

-

-

12 C18:2

trans

trans

cis

cis

(

(

-

-

9,

9,

-

-

11 C18:2)

cis

cis

trans

trans

vaccenic acid

(trans-11 C18:1)

-

-

10 C

10 C

trans

trans

18:1

18:1

stearic acid (C18:0 )


Milk fat concentration
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
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

1.5

1.0

Secretion Rate (kg/hr) (____)

0.5

0


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)

Item Milk yield Fat% Protein %

# studies 40 18 4

2X 42.9 3.65 3.10

3X 50.6 3.51 3.05

# studies 4 3 3

2X 54.6 4.71 3.49

4X 64.5 4.53 3.44


Milk Let Down

  • Refractory period to oxytocin?

  • Adrenaline interferes


Milk Ejection

brain

nerves

P.P.

Stimulus


Milk Ejection

nerves

P.P.



Milk Ejection

Abdominal aorta

Oxytocin

Jugular vein

heart


Milk Ejection

Oxytocin


Milk Ejection

Oxytocin





Contraction of an Alveolus

arteriole

venuole

Lumen

Myoepithelial Cell

Oxytocin

Duct


Contraction of an Alveolus

Oxytocin

Myoepithelial Cell contracts


Contraction of an Alveolus

Releases milk into

duct system


Contraction of an Alveolus

Myoepithelial cell relaxes






Biosynthesis of milk components
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
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)



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