Identification, properties, and differential counts of cell populations using electron microscopy of dry cows secretions, colostrum and milk from normal cows.

Differential counts of electron microscope sections of cell pellets isolated from bovine udder secretions showed that no secretory epithelial cells and very few ductal epithelial cells were present at any stage. The predominant cell type was the macrophage in dry and lactating cows or the polymorphonuclear leucocyte (PMNL) in colostrum. Lymphocytes were also present but no plasma cells were found. The macrophages took up polystyrene latex particles (as did the PMNL) and adhered to glass in culture. Neither macrophage- nor PMNL-rich cell suspensions produced any increase in free fatty acid levels when incubated with fresh milk.