Low somatic cell count and susceptibility to mastitis in dairy ruminants

Abstract

The concentration of milk cells, or somatic cell count (SCC), is an indirect indicator of mammary infection, which is widely used in the epidemiology of mastitis. It is also a predictor of intra-mammary infection susceptibility used for selection of dairy ruminants resistant to mastitis. Owing to the role attributed to milk cells in the immune protection against mastitis, the selection of animals with very low SCC has given rise to doubts and criticism, fearing that selection would lead to an increased susceptibility to mastitis. Epidemiological surveys have yielded apparently contradictory results, which did not settle this issue. Nevertheless, by taking into account the immunobiology of the mammary gland, along with the results of recent studies on SCC-based divergent selection of dairy animals, it is possible to give a definite answer to the question “Should we avoid selecting dairy animals with very low SCC?” It clearly appears that the selection does not reduce the baseline SCC of uninfected healthy glands and does not weaken the capacity of the mammary gland to defend itself against infections.