Mimeo DH-101
October, 1964
Structure and Function of the Cow’s Udder
P. L. Hill, W. M. Dillon and J. L Albright, Animal Sciences Department
Most dairy cows efficiently convert feed into milk. The focal point in this process is the udder or mammary gland. Originally the cow secreted enough milk to nourish the young. Over a very long time, improved selection and feeding have resulted in increased milk production and greater development of the mammary gland. Increased knowledge of the structure, growth and function of the udder should help dairy farmers take better care of their cows and obtain increased returns.

Composition of the Udder
The cow's udder consists of four glands which are grouped together--two on each side--to form halves. It varies in weight after milking from less than 10 to more than 150 pounds. The udder is attached to the body by median and lateral supporting ligaments. The median suspensory ligament is composed of fibers that come out of the lower abdominal wall and spread into each half of the udder. It is elastic and stretches to allow the udder volume to change with minimum lowering of the udder floor. The lateral suspensory ligaments are composed of inelastic tissue and cover the upper outer surface of the udder. If the median suspensory ligament does not have sufficient strength, the udder is said to be breaking away. This condition usually results in longer and more difficult milking and greater chance of injury.
Each quarter functions independently and has its own outlet, the teat. At the lower
end of the teat is an opening made up of a streak canal surrounded by a circular muscle. If this muscle is strong and the streak canal is narrow, the cow is a hard milker. If it is relatively weak and wide, she is an easy milker. The teat cistern holds about 1 ounce of milk and it connects to the gland cistern that varies considerably in size and shape.
The gland cistern usually holds about 16 ounces of milk and has 8-12 large ducts emptying into it.

Where Milk is Manufactured
The large milk ducts branch and rebranch into collecting tubules that begin at each alveolus, which is the basic milk-producing unit in the udder. These microscopic alveoli are so numerous in the more highly efficient glands that they occupy practically all the available space. After udders of this type are milked out, they seem to "shrink away" to nothing and are free of excessive connective tissue. Other necessary internal structures of the udder include the blood supply, supporting tissue, the lymphatic system and nervous tissue.
Dairy Section • Animal Sciences Department
Cooperative Extension Service, PURDUE UNIVERSITY, Lafayette, Indiana