Milk Protein, Colostrum, Lactose, Minerals and MUN

Milk Proteins (Caseins)• Found in milk in the form of a Micelle (a dense protein granule). The phosphate groups

covalently bound to the casein molecules are involved in binding Calcium (Ca) via ionic bonds. After caseins are phosphorylated, Ca++ binds to the phosphate to initiate polymerization of the micelle particles. This [casein-PO4- Ca++ - PO4-casein] structure is key to micelle formation.

• The casein micelle functions as a source of nutrients for the neonate: supplying amino acids, calcium and phosphate.

• Micelles are ~140 nanometers in diameter. They are composed of alpha- , beta-, and kappa-caseins. a-Caseins are in multiphosphorylated forms. ß-Casein is a major casein in cow milk, but is the minor casein in human milk. k-Casein (a glycoprotein) is distributed throughout the casein micelle and acts to stabilize the micelle. Gamma-caseins (part of the proteose peptone fraction of milk) are C-terminal fragments of ß-casein, which are released by plasmin digestion, mostly while the milk is in the gland.

• The destabilization of the casein micelle structure and partial hydrolysis of casein decreases the quality of fluid milk and the yield of cheese from milk. Conversely, the destabilization of the casein micelle by proteases is part of the mechanism involved in milk digestion in the stomach and intestine. Controlled hydrolysis of casein is also the means of producing cheeses and other cultured milk products.

Milk Proteins

Casein Micelle Structure

Mouse Casein Micelles

Milk Proteins (Major Cow Whey Proteins)

• ß-LACTOGLOBULIN (ß-LG): Is ~50 % of the total whey protein content in milk. Is the major whey protein in ruminants and pigs. It is not found in milk of many species. The function of ß-LG is unknown; it may be a fatty acid or lipid binding protein. It does have sequence similarities with retinol-binding proteins, but this may not be its function. Generally it is found in milk of species which transport high levels of immunoglobulins during colostrum formation, however the specific relationship between the presence of ß-LG and immunoglobulin transport remains unclear.

• a-LACTALBUMIN (a-LA): Is ~25 % of the total whey protein content in milk. Is the "B" protein of the Lactose Synthase enzyme complex . Therefore, it is of major interest in terms of the control of milk secretion. May have other nonspecific effects on the integrity of milk fat membranes. a-LA binds Ca and Zn.

Milk Proteins (Minor Cow Whey Proteins)

• SERUM ALBUMIN (SA) : Serum albumin comes from the serum; it is not synthesized in the mammary gland. It is presumed to enter the milk via "leakage" by the paracellular pathway, or by uptake with other components such as immunoglobulins. There does not seem to be a more specific mechanism of transport. Increases in milk concentration of serum albumin occur especially during mastitis and during mammary involution. Function of serum albumin in milk is unknown. It does bind to fatty acids, as well as other small molecules.

• IMMUNOGLOBULINS (Ig): include IgG1, IgG2, IgA, IgM : Immunoglobulins are in very high concentrations in colostrum, but much lower concentrations in milk. Immunoglobulins are part of the passive immunity transported to the neonate via colostrum in many species. They are part of the mammary immune system. Secretory Component (SC) is the part of the IgA receptor which hydrolysed by a protease and remains attached to IgA as it is secreted from the cell.

Milk Proteins (Minor Cow Whey Proteins)

• Lactoferrin (LF) - Is an iron binding protein and has antibacterial properties. Relatively low concentrations during lactation in cow milk, but is increased during mastitis and involution. Lactoferrin may also be an immunomodulator. Lactoferrin is in human milk in high concentrations; in fact it is the major whey protein in human milk. Lactoferrin is the major nonspecific disease resistance factor found in the mammary gland.

• Lactoperoxidase - Is an enzyme that breaks down hydrogen peroxide. It has antibacterial properties.

• Lysozyme - Is an enzyme that cleaves the carbohydrate polymers of the bacterial cell wall. High activity in human milk and possibly in horse milk, but very low activity in cow milk.

Cow Milk Protein Variants

Colostrum

Milk Composition in Early Lactation

Concentrations of Antibodies

Antibody Structure

CH3

CH2

CH1

Antibody IgG1, 2, 3, 4, IgM, IgA Heavy ChainsAntibody Kappa, Lambda Light Chains

Antigen

Antibody Structure

IgG Antibody Structure

IgA and IgM Antibody Structure

Feeding Colostrum

Pooling Colostrum

Colostrum Quality

Colostrum Quality on Calf Survival

Saving Colostrum

Lactose Production

Lactose Biosynthesis

Sources of Glucose

Utilization of Glucose in the Bovine Mammary Gland

Metabolic Regulation of Lactose Production

Alpha-lactabumin

A major whey protein in bovine, porcine and human milk. ~ 1.2 g/L in bovine milk and 1.5 g/L in porcine milk Important source of dietary amino acids for calves, piglets and

infantsContains a higher percentage of the essential amino acids (Threonine,

Methionine, Lysine, Valine, Leucine, Isoleucine, Histidine, Phenylalanine, Tryptophan, Alanine) than the other major milk proteins

Combines with ß1,4 galactosyltransferase within mammary epithelial cells to form “lactose synthase”.

Lactose is the primary osmole in milk, which, in turn, regulates milk volume.

The most tightly controlled milk protein gene to lactation

Alpha-lactalbumin Production During Pregnancy

Alpha-Lactalbumin Levels in Serum at Calving

Beta 1,4 Galactosyltranferase

A enzyme found in the golgi apparatus of all cells.

Normally involved in glycosylation of proteins

Combines with alpha-lactalbumin within the mammary epithelial cells to form “lactose synthase”.

Alpha-lactalbumin modifies Beta 1,4 Galactosyltransferse’s normal function causing it to hook glucose and galactose together to form lactose

Lactose Synthesis

Mammary Epithelial Cell Cartoon

Alpha-lactalbumin Knock-out Mice

Phenotype of Alpha-lactalbumin Knock-out Mice

Phenotype of Beta 1,4 Galactosyltransferase Knock-out Mice

Production of Bovine Alpha-lactalbumin in Transgenic Sows

Lactose Production in Alpha-lactalbumin Transgenic Sows

Day of Lactation

% (g/dL)

Mean ± SEM

* p < 0.05

22.5

33.5

44.5

55.5

6

0 2 4 6 8 10 12 14 16 18 20

* **

Transgenic(n=8)

Control (n=10)

*

Milk Protein % in Alpha-lactalbumin Transgenic Pigs

Milk Production in Alpha-lactalbumin Transgenic Sows

Day of Lactation

Mean ± SEM

* p<0.05

012345678

Milk Yield (kg/d)

3 6 9 12

**

*Transgenic(n=8)

Control (n=10)

Growth of Piglets Nursed by Alpha-lactalbumin Transgenic Sows

kg

Day of LactationMean ± SEM * p<0.05

00.5

11.5

22.5

33.5

4

2 4 6 8 10 12 14 16 18 20

d 0

d 20

Control(n=200)

TG(n=200)

1.46 ±0.03

1.42 ±0.02

4.48 ±0.07

4.91 ±0.05 *

Cumulative Weight Gain Mean Weight (kg)

*

TransgenicControl

*

* d 7-21

Weight Gain by Piglets Nursed by Alpha-lactalbumin Transgenic Sows

Mean Rate of Piglet Gain Throughout Lactation

0

0.05

0.1

0.15

0.2

0.25

mea

n ra

te o

f gai

n (k

g/d) *

control transgenic

Ion Movement into Milk

Transfer of Calcium and Phosphorus into Milk

Altered Lactose and Ion Content in Milk

Milk Urea Nitrogen (MUN)

Using MUN

Individual and Daily MUN Samples

High MUN Values

Low MUN