| "No!" says Dr. Leo Timms of Iowa State University. Because what is
involved is more than cell numbers, explains Dr. Timms. Somatic cells are
white blood cells or body defense cells. Their primary functions are to
eliminate infections and repair tissue damage.
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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