Electrical conductivity and chloride concentration of milk as auxiliary diagnostic methods in bovine subclinical mastitis

Electrical conductivity measured by a hand-held meter and chloride concentration of milk were Studied as auxiliary methods for diagnosis of bovine subclinical mastitis in the identification of affected mammary quarters where Staphylococcus aureus and Corynebacterium sp were later isolated. Tests were made during 2 years in Holstein cows of a dairy farm producing type C milk, where milking was performed once a day. Sensitivities of electrical conductivity and chloride concentration tests from mammary quarters, where Corynebacterium sp was isolated (65.3% and 78.3%, respectively), were superior to the found in mammary quarters where S. aureus was identified (55.4% and 68.2%, respectively). The efficacies of the two diagnostic tests were similar. Statistical significance was demonstrated with regression analysis of both tests of healthy mammary quarters and subclinical mastitis quarters infected with Staphylococcus aureus.