Effects of mastitis on raw milk and dairy products

This review covers scientific and technical publications from 1982 to 1996 on the influence of mastitis, both clinical and subclinical, on raw milk yield and composition and dairy product yield and quality. In some cases, earlier references are provided for clarification. It provides an update for the reviews of Kitchen (1981) and Munro et al. (1984). The review examines somatic cell count (SCC) as a measure of mastitis; the effect of SCC on the yield and quality of raw milk and dairy products; the SCC threshold affecting milk products; seasonality and late-lactation milk; milk quality incentive schemes for SCC; and mastitis control practices and SCC. The literature reviewed confirms the deleterious effects of mastitis on milk composition and the yield and quality of dairy products. Other factors that alter milk composition (e.g. season, stage of lactation, nutrition) sometimes confound the precise effects of SCC. A SCC standard of 400,000 cells/mL for bulk milk is being adopted in milk quality schemes around the world as a result of the European Union requirements which apply from January 1998. This level will minimise the effects of mastitis on product quality, although negative effects on product quality have been reported for milk with a SCC as low as 100,000 cells/mL. Further, a bulk milk somatic cell count of 400,000 cells/mL indicates that around 40% of cows in a herd are infected.