Abstract
Prototheca zopfii is associated with bovine mastitis, which causes a reduction in milk production and secretion of thin, watery milk with white flakes. However, the source of infection and an infection route of mastitis have not been clarified. In this study, we evaluated the prevalence of P. zopfii genotype 2 in fecal samples from Japanese dairies with or without a history of protothecal mastitis in 2017. P. zopfii genotype 2 was detected in 23 of 60 (38%) fecal samples in only the herd with a history of protothecal mastitis. These results suggest that occurrence of bovine protothecal mastitis is related to persistent infection in intestine and the source of infection is feces.