Effect of the Season on Blood Changes of Oxidative Stress Index in the Italian Mediterranean Buffalo (Bubalis bubalis)

Studies in cattle have shown that high temperatures increase the production of reactive oxygen species (ROS) causing an imbalance between ROS and the ability of antioxidant systems to detoxify and remove the reactive intermediates. As such studies remain limited in buffalo, the effect of temperature on oxidative stress was investigated through the oxidative stress index (OSi). Blood samples were collected from 40 buffaloes over 12 time points distributed over two years (2021, 2022). Samples were taken monthly during the hot and cold seasons. Plasma free oxygen radicals were determined using the d-ROMs test (Diacron, Italy), modified for a microplate procedure, and the results were expressed in arbitrary Carratelli Units (U.CARR). Plasma antioxidants were determined by using the BAP test (Diacron) in a dedicated spectrophotometer (Carpe Diem Free, Diacron). The OSi parameter was calculated as d-ROMs/BAP × 100. Temperature and humidity were recorded daily during the trial to calculate the Temperature Humidity Index (THI). For statistical analysis, year and season and their interactions were included in the model. The results of this study showed for the first time the effect of season on the oxidative stress in buffalo. The minimum and maximum THI values for the hot and cold season recorded during the experimental period were 79.27 ± 2.20 and 63.42 ± 3.20, respectively. Levels of d-ROMs and BAP were affected by the seasons (133.0 vs. 145.1 U.CARR, <i>p</i> = 0.0189, and 2489.19 vs. 2392.43 mml/L, <i>p</i> = 0.033, in the hot and cold season, respectively). A significant year × season interaction was found both for d-ROMs and BAP (<i>p</i> = 0.06 and <i>p</i> < 0.0001, respectively). Moreover, OSi was affected by season, showing a growing trend from hot to cold season (5.35 vs. 6.17, <i>p</i> < 0.0001), but, interestingly, it was unaffected by annual variation. Therefore, Osi could be considered a better and independent marker of oxidative status in buffalo, with respect to the evaluation of single determinations of d-ROMs and BAP. Lastly, there were no differences in the plasma 25OHD levels between seasons; concentrations were 12.24 and 10.26 ng/mL in the hot and cold season, respectively.