Structure of udder: The udder is located outside the body wall and it attached to it by means of its skin and connective issue supports.
The secretary portion of the udder consists of countless alveoli or chambers lined with individual cells. Each of these alveoli is drained by a small duct which leads to larger ducts. Clusters of alveoli resembling a bunch of grapes are drained by ducts of increasing size until some 10 to 20 ducts conduct milk into the gland cistern. The gland cisterns continue into the teat sinus or cistern. At i he tip of (he teal there is a sphincter tightly closing the outlet of the teal sinus.
Each alveolus is-supplied blood through tiny capillaries which lie outside the secretary cells. Small muscle fibers also surround each alveolus and are important in the removal of milk from the gland. The individual secretary cell is the primary factor in milk production. It extracts all of the components of milk from (he blood stream and either arranges them into new compounds or passes them through directly into the alveolus.
The milk Leldown mechanism:
When milk secretion has continued for a considerable time after milking, the alveoli, ducts and gland and teat cisterns are filled with milk. Milk in the cisterns and larger ducts can be removed readily. Milk in the smaller duels and alveoli does not flow out easily. However, the cow and other mammals have developed a mechanism for releasing milk from the mammary gland. Stimulation of the central nervous system by something associated with the milking process is necessary to initiate the read ion. Stimulation of nerve endings in the teats that are sensitive to touch, pressure, or warmth is the usual mechanism. The suckling action of the calf is ideal for this. However, massaging the udder or washing with warm water is also equally effective. Stimulation is carried by the nerves to the brain which is connected. With the pituitary gland located its base. Mechanisms are activated in the pituitary gland which causes the liberation of a hormone oxytocin from its posterior lobe. Oxytocin is carried by the blood stream lo the udder where it acts on the small muscle rolls surrounding the alveoli, causing them to contract. The pressure thus created forces the milk out of the alveoli and smaller ducts as fast .is it can be removed from the teat.
The letting down process can be stimulated within half to one minute’s time. The effective time of the hormone is limited and milking should be completed within seven minutes if all the milk is to be obtained.