A polymerase chain reaction based study on the subclinical mastitis caused by Streptococcus agalactiae, S. dysgalactiae and S. uberis in cattle in Ahvaz

Streptococcus agalactiae , S. dysgalactiae and S. uberis are Gram-positive bacterial pathogens that affect cows in dairy herds. These are considered as the major causes of economic losses of dairy producers without a control program. To reveal the role of these agents in inducing subclinical mastitis in dairy cattle in Ahvaz, 100 CMT-positive milk samples and 20 CMT-negative milk samples were collected and examined by polymerase chain reaction (PCR). The results were compared with the conventional bacterial culture. Based on the PCR results, S. agalactiae, S. dysgalactiae and S. uberis  were causative agents in 20, 12.5 and 0.83% of samples, respectively. There was not any culture-positive samples being negative in PCR, but there were 10 PCR positives being negative in culture method. Based on McNemar test, there was 91.6% agreement between PCR and culture methods for the diagnosis of streptococcal mastitis. There were 14 and 7 CMTnegative samples, being positive by PCR and culture methods, respectively. The results of this study showed that subclinical infections from these bacteria are prevalent in dairy cattle of Ahvaz and regular testing and control programs should be planned to control the infection. CMT has not sufficient sensitivity for detection of subclinical mastitis due to these agents.