Subclinical mastitis is also as a consequence of bacterial infection (Arsenault et al. 2008) and normally results in the ewe being well overall, but having infection in the udder. The categorisation of clinical and subclinical mastitis depends very much on the degree of inspection given to an animal. In meat sheep it is quite likely that changes in milk alone are not detected by farmers and so these fall into the category of subclinical infection. In milk sheep and dairy cows such changes would be detected because the udder and milk are inspected twice each day. Subclinical mastitis can lead to a reduction in milk yield and altered milk composition (Bergonier & Berthelot 2003; Conington et al. 2008; Fthenakis & Jones 1990).
There is no universally accepted definition of subclinical mastitis with no established ‘normal’ somatic cell count and as such different studies may define cases differently.