Subclinical mastitis is the most prevalent and economically destructive disease in dairy cattle throughout the country. It is 3–40 times more common than clinical mastitis and causes the greatest overall losses in most dairy herds. It is a multi etiological complex disease which consists infectious and noninfectious agents as potential risk factors. The prevalence of subclinical mastitis in cows increases with increased milk production, unhygienic management practices and with increasing number of lactation. There are no visible changes in the udder or milk but it reduces milk production and adversely affects milk quality. Early detection of sub clinical mastitis can be done by various indirect and direct tests.