These cells are constantly circulating in the blood stream. When infection occurs, the body sends high quantities of somatic cells to the injured site. 

Phagocytes are the primary somatic cells in the mammary glands. Their purpose is to engulf (phagocytize) and destroy bacteria, flooding the infected site until most of the organisms are destroyed. Lymphocytes, T. lymphocytes and B. lymphocytes are other types of somatic cells. 

Somatic cells and the immune response are very specific. Somatic cells are sent only when and where needed. High somatic cell counts indicate mammary infection and the body's response by sending somatic cells to destroy the infection. 

Dr. Timms points out that there is always a circulating army of cells waiting to be dispatched to areas of infection or irritation in the udder. There is no need for high cell counts in the udder when there is no infection. 

Importantly, Dr. Timms stresses that the presence of somatic cells in the udder when there is no infection can actually harm the gland. Somatic cells can damage epithelial cells and other cells causing the release of enzymes from dying cells. 

If only cell numbers were involved, a cow with one million SCC could not harbor an infection like S. aureus. 

Research shows the importance of cell competency (ability to do the job). Tests of chronically infected S. aureus cows, with high SCC, show lymphocytes unresponsive to stimulation compared to uninfected animals. Phagocytic (destroying) ability of milk leucocytes was also reduced, and high numbers of phagocytic cells had a detrimental effect on lymphocyte function. 

Dr. Timm's conclusion: "The key is healthy animals. If an animal is healthy, she'll respond to mammary infection with adequate cells, regardless of how low her SCC is. The lower the better, is the bottom line on somatic cell counts." 

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