Milking is the technique by which milk is extracted from the udder of the dairy cow. The udder is a gland delegated to the production and secretion of milk, first food of mammals, it is a composed tubulo-alveolar gland, considered to be the most evolved skin gland. The mammary gland is composed of alveoli which synthesize and secrete and small ducts which are needed to secret the milk. The glandular mammary tissue is divided into lobes in which each one contains many lobules. Each lobule contains clusters of alveoli and is surrounded by connective tissue. You can consider each alveolus like a single milk producing unit of the udder. The number of cells for each alveolus increases in dairy breeds, due to the presence of a specific chromosome set or for genetic selection carried out on the breed. This therefore implies that in dairy breeds there is a greater number of cells per alveolus, larger size of the alveolus and a greater unit volume, which means a greater capacity of synthesis and secretion of milk. Morphologically the dairy cow’s udder is subdivided into quarters, each one is served by a nipple: the fore and rear quarters. The rear quarters on average produce more (about 50/60% of the total production).
How is the milk produced in the udder?
The milk is produced in the udder by amino acids transported in the blood, that once in the udder are used to synthesis proteins like: lactoglobulin, lactalbumin and membrane proteins. The proteins produced together with the synthesized lactose and the minerals are released into the lume of the alveolus by exocytosis with the release of water, lactose, casein micelles and whey proteins. Milk is produced thanks to the blood supply which transports the fundamental elements for the production of milk in the udder. This involves a high metabolic activity, considering that to produce 1 litre of milk the equivalent of approximately 400 litres of blood has to pass through the udder, that is for one cow, who on average produces 35 litres of milk per day, approximately 14.000 litres of blood per day flow through the veins in the udder, equal to about 15% of the cardiac work of a cow.
| Composition of milk
| Specific weight
| Total Protein
Therefore, the importance of water is understandable in dairy farms. Cow drink up to 200 litres of water per day.
The main hormones involved in the production and secretion of milk are secreted by the pituitary gland and are:
- Produced by the posterior pituitary gland, it makes the myoepithelial cells to contract
- Produced by the anterior pituitary gland, it is responsible in maintaining the continuous production of milk
- Secreted by the anterior pituitary gland it stimulates the production of milk, increasing the blood flow.
How is the milk released from the cow?
The majority of the milk accumulates inside the alveoli. The milk ejection reflex begins with nerve stimulation, whose impulses are interpreted by the brain (hypothalamus) to alert the cow that milking is imminent. The external stimuli such as physical touching of a calf, or a operator who cleans the teats, the visual contact with a calf or the sound of the milking machine, lead the brain to send a signal to the pituitary gland which releases oxytocin into the blood flow. The blood transports the oxytocin to the mammary gland. Here the oxytocin stimulates the contraction of the small muscles (the myoepithelial cells) which surround the alveoli which are full of milk. The squeezing action increases the intramammary pressure and forces the milk through the ducts towards the gland cistern and the teat cistern. The oxytocin effect only lasts for 6-8 minutes, because its concentration in the blood diminishes rapidly. It is therefore important to attach the cluster to the teats within 1 minute after the preparation of the udder. Delay in attaching the cluster can also reduce the quantity of milk produced, because milk from the udder will be retained and not released. In certain situations, milk ejection can be inhibited. This can occur during milking if unpleasant external events take place (pain, a fright or fear) and therefore the milk is retained by the udder.
The hormone adrenaline, released by the pituitary gland, can narrow the blood vessels and capillaries of the mammary gland. This decrease in blood flow leads to a decrease in the amount of oxytocin that reaches the mammary gland. Besides that, adrenaline seems to directly inhibit the contraction of the myoepithelial cells of the mammary gland. Therefore, the cow cannot be milked quickly or completely in the following situations:
- If the preparation of the udder is inadequate;
- If there is a few minutes delay in attaching the cluster after the preparation of the udder;
- When unusual circumstances cause suffering (for example, when the animal is hit) or frightened (shouting, sudden noises);
- In the case of inadequate functioning of the milking machine;
The drop down (release of milk from the alveoli) occurs due to neuromuscular stimulation: the stimulus which can be of different nature, facilitates the release of oxytocin, a hormone responsible for the contraction of the alveoli. The stimulus can be of different types:
- physical/mechanical, due to the farmer as he cleans the teat;
- visible, due to the sight of a calf by the cow;
- noise, due to the rhythmical sound of the milking machine.
These stimuli make the milk arrives in the teats after about 40 seconds. It is therefore important not to attach the cluster to the udder before this time. Incorrect milking, due to the inhibition of the myoepithelial reflex, could be due to:
- an incorrect preparation of the udder;
- pain, fear (caused by loud noise, sudden movements, beatings, slippery floor ...) that cause the release of adrenaline which is a vasoconstrictor that slows the flow of oxytocin
Firstly, it is preferable to do 2 milkings each 12 hours, this is to give the udder a set timetable.
- The cow must enter the milking parlor calmly. The parlor must be very bright, this motivates the cows to enter;
- The milker must evaluate the foremilk (if there are small clots there is probably inflammation);
- The milker must proceed with the cleaning of the teats with disposable cloths, he must then dry them properly;
- He must attach the cluster within one minute. The vacuum must be controlled accurately: there is a risk that it could damage the teat;
- The milker must monitor the transparent tubes to control the smooth passage of milk.
- The milker must verify that the automatic turn off is perfectly set for that particular cow;
- The milker must clean the teat after milking: only after about an hour the sphincter blocks the teat. Proceed with a liquid antibiotic solution.
- The farmer must make sure that the cow remains on its feet, the bedding is full of pathogenic microbes. He must therefore make sure that the cow (which will be hungry after milking) has the possibility to easily access the feeding trough and that feed is available.