The cell content of milk is composed of approximately 95 percent leukocytes (white blood cells) from the blood and 5 percent epithelial cells from the secretory tissue of the udder. Leukocytes are present in response to infection or injury, and epithelial cells are present as a result of infection or injury. Collectively, these cells are called somatic cells.
All the cells (often referred to as body cells) of a multicellular organism other than the sex cells ( gametes). Somatic cells reproduce only by the process of mitosis; changes in such cells are not heritable, since they are not involved in germ-line reproduction as sex cells are.