Background: Thiol/disulphide homeostasis (TDH) has a critical role in many cellular activities such as antioxidant protection. Alterations of oxidative stress in the transition period play an important role in development of some diseases and disorders in dairy cows.Objectives: The purpose of this study is to assess the total antioxidant status (TAS), total oxidant status (TOS), oxidative stress index (OSI), total thiol, native thiol, disulphide and lipid profile in Simmental and Montofon dairy cows (aged 2–3) before and after calving.Methods: Blood samples were collected 233–280 days of pregnancy and the 30 days of post‐partum. Serum total thiol, native thiol and disulphide levels were determined as well as TAS, TOS and paraoxonase‐1 (PON‐1) levels were measured using colorimetric assays. Triglycerides (TG), total cholesterol, HDL cholesterol and LDL cholesterol levels were measured with an automatic analyser.Results: Total thiol (p = 0.038) and disulphide (p = 0.015) levels were higher after calving compare to pregnancy in Montofon. TAS was found lower (p < 0.001), and OSI was higher in both breeds (Montofon p = 0.012, Simmental p = 0.028) after calving than in pregnancy. When compared between pregnancy and after calving levels in the same breed, HDL was found to be higher after calving (p < 0.001) and TG was lower after calving (p = 0.020) in Montofon. PON (p = 0.090), HDL (p < 0.001) and cholesterol levels were found higher (p < 0.001) and TG level was lower (p < 0.001) after calving in Simmental.Conclusions: According to our results, we observed different responses between two breeds before and after calving. There are few studies about TDH in animal research, and this is the first study in the literature that evaluates the TDH along with oxidative stress and lipid profiles in dairy cows in the periparturient and post‐partum period.

Background: Accurate measurement of enzyme activities is very important in studies to evaluate enzymatic parameters. While performing these measurements, many factors can affect the results, including the method of obtaining the tissues, the conditions under which they are stored until analysis, and the methods of determining enzyme activity. Objectives: This study aimed to investigate the effect of different storage conditions (time and temperature) and different homogenisation buffers (PBS or KCl) on the enzymatic activity of superoxide dismutase (SOD), catalase (CAT), and adenosine deaminase (ADA) in homogenised cattle liver. Methods: Fresh liver tissue samples were obtained from the slaughterhouse and homogenised in different homogenisation buffers. Supernatants from each sample were divided into three groups according to the experimental design of the study. SOD, CAT and ADA enzyme activities in homogenised tissues were evaluated. Results: Our data revealed that SOD, CAT and ADA activities did not differ significantly between PBS and KCl groups or between ‐20°C and ‐80°C freezing temperatures. However, our results showed that SOD levels decreased over time in both groups, CAT levels demonstrated a significant decrease from Month 0 to Month 3 and ADA levels decreased significantly over time. Conclusions: The results indicated that storage time had a significant effect on enzyme activity changes, but the effect of storage temperature and homogenisation buffer was generally limited. These results may support the measurement of enzymatic activity in liver homogenate immediately and, if necessary, after freezing for the shortest possible time.