Pre- and post-treatment oxidative stress markers, serum amyloid A and metabolic variables in dairy cows with Staphylococcus aureus subclinical mastitis

The objective of the current research was to compare oxidative stress markers, metabolic variables and serum amyloid A (SAA) in dairy cows with Staphylococcus aureus subclinical mastitis before and after treatment and to evaluate their correlation with treatment outcome. Oxidative stress biomarkers, including total antioxidant capacity (TAC) and malondialdehyde (MDA) and SAA were measured in milk samples and non-esterified fatty acids (NEFA), glucose, calcium and magnesium were determined in blood serum samples of two groups of cows: 1) S. aureus subclinical mastitis cows with unsuccessful treatment (UST group; S. aureus isolated in bacterial culture and somatic cell count (SCC) ≥ 200,000 cells/mL in milk samples obtained before and after treatment; n=26), and 2) S. aureus subclinical mastitis cows with successful treatment (ST group; negative bacterial culture and SCC < 200,000 cells/mL in milk samples obtained after treatment; n=26). Successful treatment signi­fi­cantly decreased milk SCC and SAA and serum NEFA (P<0.05), while significantly increased serum calcium, magnesium and glucose levels (P<0.05) in ST cows. After unsuccessful treatment, mean milk SAA dropped significantly (P<0.05) while milk TAC and SCC and serum calcium levels increased (P<0.05) in UST cows. The findings of the present study showed that the improvement of negative energy balance (observed as decreased NEFA and increased glucose concentration following successful treatment) might be an important variable for the treatment outcome of S. aureus subclinical mastitis in dairy cows