THE ENDOCRINE SYSTEM

This system consists of numerous ductless glands throughout the body, which secrete chemical messengers called hormones. Some such hormones are examined in the table below:

IN the cow, the udder is the structure responsible for milk production. It is located underneath the abdomen, near the hind legs and consists of four quarters, each completely separate from one another. This can be advantageous should the udder become infected with disease such as mastitis as it will be contained in one quarter and not spread throughout the udder.

Prolactin is responsible for the production of milk in mammals. A well-developed udder and supporting ligaments is an important criterion in selecting an animal for breeding. Suspensory ligaments are the muscular support for the udder, which can hold up to 40kg of milk.

The internal structure of the udder is glandular tissue consisting of millions of alveoli. Each alveolus is a cavity surrounded by muscles, blood capillaries and cells which secrete the milk. Milk production and let-down may be summarised as follows:

The brain interprets certain stimuli through sight, smell and sound to indicate milking is about to commence. Such stimuli include rattling of milk buckets or approach of the milker.

When the udder is stimulated by a calf sucking or attachment of the milking machine, a message is sent to the brain.

The pituitary gland in the brain responds by secreting oxytocin, which causes contraction of the muscles of the alveoli and secretion of milk into the cavities.

The milk travels out of the udder through the teat canals. The milk ejection usually takes 30-40 seconds after the initial stimulation and the whole process known as ‘milk let-down’ takes up to six minutes.

Cows should be subjected to minimal stress during milking as stress can trigger the release of another hormone adrenaline which counteracts the effect of oxytocin.