The anatomy of the udder
The udder is an organ designed to produce milk, composed of four individual mammary glands. A strong membranous wall — the medial (central) suspensory ligament — separates the right and left quarters. This membranous wall, along bands of connective tissue, enables the suspension of the udder to the cow’s abdominal wall. Although the division of the front and rear udder quarters is not clearly visible it is certainly present (figure 1).
Milk is synthesized in the glandular tissue of the udder. Important elements of the glandular tissue are the duct system for storage of milk, and the milk-secretory cells – alveoli – in which milk is produced and from which it is secreted. The alveoli vary in size from 0.10 to 0.50 mm, depending on the extent of filling.
Milk is synthesized in the milk-producing cells. The components required for the synthesis of milk are drawn from the blood through osmotic processes. This takes place where the small blood vessels (capillaries) come into contact with the milk-producing cells. Some components are drawn
from the blood without undergoing any change. However, the main components need to be built up, and for this energy is needed.
Blood is of major importance for the formation of milk, as approximately 400 to 500 liters per kg milk is pumped through the udder. Two milk veins carry blood from the udder to the heart together with two veins in the abdominal cavity. Two arteries carry blood to and from the udder. When a cow is lying down, 20% more blood flows through the udder; therefore, it is important that cows are able to lie down for sufficient periods. The udder also contains lymphatic vessels that carry lymph from the teats to the lymph nodes located above the mammary gland. The lymph glands have a filtering function (the removal of waste material).
Cows may spend at least 14 hours a day lying down, but they are not ‘just resting’. As we have seen, this time is essential for milk production. When cows are lying comfortably there is no stress on their feet and legs, which results in more activity once they are standing again. Therefore, in addition to comfortable resting space, free cow traffic and fresh flexible feeding are also of crucial importance.