How is goat milk produced?

Alveoli are the milk producing structures of the mammary gland. Each alveoli has a rich supply of blood that brings the components to produce milk to the cells. Alveoli are linked with Capillaries that bring the components and Venuoles that remove excess fluids. About 500 volumes of blood must pass through the udder to maque 1 volume of milk.

The lining of each alveolus is composed of cells (Epithelial cells) that surround a cavity called the lumen.

The Epithelial cells

The Epithelial cells act like factories, let’s explore it’s functions in milk production

As all cells, epithelial cells need energy to work.

One of the products by microbian fermentation in the rumen is propionic acid. It is absorbed into the blood and transported to the liver where it is converted to glucose. More than half of the glucose that will get to the alveolus will be used as a source of energy for the cells ( the other half will be used to crate lactose). CH3CH2COOH C6H12O6

The epithelial cells need to synthetise components of milk that are not present in blood such as lipids (fats), some proteins and lactose (milk’s sugar). The cells control by the way the amount of each component in the milk.

Lipogenesis is the process where syntesis of milk fats is done. This fats are manufactured from precursors brought to the cells by blood.

A fatty acid is a molecule that has a long or short of carbon atoms whit this structure at the end. Where C=Carbon, O=Oxygen and H=Hydrogen (here an example with an acetic acid).

Acetic acid (C2H4O2) and β –hydroxybutyric (C4H8O3) are also products of the rumen fermentation and are the main precursors of milk fatty acids synthesis in the mammary gland. In a complicated series of steps, the acids are combined to crate a long chain of fatty acid called palmitic acid.

Palmitic acid has a 16 carbon atoms in it’s chain.

Palmitic acid can be used to synthetise fat or it can be broken down into a shorter chain fatty acid such as carpic acid. Wich is present in a big amount in goat milk

Carpic acid has 10 carbon atoms in it’s chain.

The percentage of fats in milk is influenced by nutrition and environment.

A fat is creted when 3 fatty acids attach to a glycerol molecule. The result is called a triglyceride, the most commun kind of fat in milk. This is a long chain triglyceride fat.

Fatty acidsGlycerol

Proteins are made from amino acids. The genes in the nucleus of the cell direct the types of proteins created. There are 20 different amino acids which are the end product of intestinal digestion of proteins. The amino acids are absorbed through the intestinal wall and transported by the blood to the liver which directs them to the body tissues as needed.

In the nucleus, a template of the DNA is created, the Messanger RNA. This copy of DNA will get out of the nucleus and counter the different amino acids. Each Messanger RNA sequence has a different code, the amino acids will be fixed in different ways and orders to form chains, the proteins.

Let’s try to understand what really happens with proteins.

Most of the protein in milk is casein. There are four kinds of casein protein:-Two types of alpha casein (α1 & α2) -a beta casein (β)-a kappa casein (κ) The four casein

forms agregate

In fluid milk, casein proteins form small spheres called micelles Alpha and Beta proteins are connected to each other by phosphate and calcium.

Kappa casein is different. It prevents Alpha and Beta casein proteins from combining with additional calcium. That’s why individual micelles repel each other.

But the Chymosin enzime, that we find in rennet, has the capability to change the kappa casein protein. We obtain para-kappa-casein which is no longer able to prevent calcium and phosphate from binding to the casein proteins. Micelles clump thus together causing the milk to coagulate. An important stem in cheese production.

β-lactoglobulin and α–lactalbumin proteins are also synthesized only in the mammary gland. Other proteins and the immune globulins are sinthesized elsewhere in the body.

Lactose is the sugar of milk. It is created only in the alveolar cells of the udder by combining glucose and galactose. Glucose is absorbed from blood. Inside the cell some glucose is converted into galactose.

Galactose is very similar to glucose except for the orientation of these molecules.

In a few more steps, Galactose and Glucose are combined to form Lactose

The alveolar cells have to regulate the amount of components that come directly from the blood but are not changed in the cell, such as water, vitamins and minerals.

Water flows through and between cells by diffusion.

The amount of minerals included in the milk is also regulated by alveolar cells.

• Major minerals:- Calcium- Phosphorus- Chlorine- Magnesium- Sodium• Trace minerals (oligo-éléments):- Iron- Manganese- Copper- Zinc

Vitamins are synthesized in the goat’s body or come directly from feed sources.

Vitamine A: Vitamine A precursor comes from plant diet and is converted into vitamine A in the wall of small intestine.

Vitamine D: comes from exposure to the sun and from some plants.

Vitamine E: comes from green feed

Vitamine K: is synthesized by bacteria in rumenand intestines. Both K and D are present in small quantities in milk.

B vitamine: is synthetized by rumen bacteria. The bacteria is broken down when it goes through the intestine and the vitamine can be used.

Vitamine C: is naturally synthesized by the goat.

The milk contains now all it’s elements and is ready to be expulsed from the alveolus. It has the following composition:

During the manufacturing of milk, lumen fills with milk.

Each alveolus is surrounded by cells called basket cells which act like muscles.

When activated by the oxytocin hormone the basket cells contract pushing the milk out of the alveoli into the collecting ducts.