Evaluation of antioxidant enzymes activity (SOD and GSH-Px) in the milk of cows with subclinical mastitis

Currently, somatic cell count (SCCs) and bacterial culture are considered as the golden standard of detecting bovine subclinical mastitis. The above- mentioned tests have a low diagnostic accuracy. For identification of infected animals, new biomarkers with high diagnostic accuracy are needed. The antioxidant enzymes change during mastitis, The objective of this study was to determine the diagnostic value of the GSH-PX and SOD for the diagnosis of subclinical mastitis in dairy cows. A total of 90 clinically healthy cows were randomly selected from dairy farms in Kohgiloye and Boyr Ahmad province, Yasouj. Of these, 55 cows were considered to be affected by subclinical mastitis based on a SCC higher than 130 × 1000 cells/mL of milk and positive CMT results of milk samples obtained from at least one of the quarters.Skimmed milk GSH-PX and SOD activites were measured using commercial kits (Randox Laboratories). Diagnostic sensitivity and specificity and cut-off points for each test were determined via receiver-operating characteristics curve (ROC) analysis. Significant increase and decrease in the mean activites of GSH-PX (P < 0.0001) and SOD (P < 0.05) were found in the milk samples collected from cows with subclinical mastitis respectively. Milk GSH-PX was the most accurate test with 100% sensitivity and 100% specificity at cutoff point of > 37 IUl/ml.The results of present study showed that the measurement of oxidative stress parameters such as GSH-PX activity in milk sample could be used as reliable biomarker for detection of bovine subclinical mastitis.