Effects of surgical timing on inflammatory responses, oxidative stress, and immune modulation in Wagyu calves following castration

BACKGROUND: Time-of-day-related physiological variation may influence immune, oxidative, and endocrine responses to surgical stress. This study evaluated the effects of morning versus afternoon surgical castration on inflammatory cytokine expression, oxidative stress markers, T-lymphocyte subpopulations, and cortisol levels in Wagyu calves. Twelve 4-month-old male Wagyu calves were randomly assigned to morning (10:00-11:30 h) or afternoon (14:30-16:00 h) castration groups (n = 6 per group). Blood samples were collected before castration and at 6, 24, and 72 h post-surgery. Inflammatory cytokine mRNA expression (IL-6, IL-10, and TNF-α) was quantified by RT-qPCR, and oxidative stress markers were assessed using TBARS and FRAP assays. T-lymphocyte subpopulations were analyzed by flow cytometry. Serum cortisol concentrations were measured by ELISA. Data were analyzed using linear mixed-effects models with Šidák adjustment for pairwise comparisons. RESULTS: Morning castration was associated with greater cytokine response, with IL-6 expression peaking at 143-fold at 6 h post-surgery, accompanied by concurrent IL-10 upregulation (13.47-fold) and a transient increase in TNF-α expression. The afternoon group showed minimal cytokine changes throughout the study period. CD4⁺ and CD8⁺ T-lymphocyte proportions were higher in the afternoon group before surgery, but were lower than those in the morning group at later post-surgical time points. γδ T cells increased at 24 and 72 h in both groups without significant surgery timing effects. Malondialdehyde concentrations were significantly higher in the afternoon group (P < 0.05), whereas total antioxidant capacity (FRAP) values were also significantly higher in the afternoon group (P < 0.05). Serum cortisol did not differ significantly between surgery time groups or sampling intervals. CONCLUSIONS: Morning surgery was associated with greater acute inflammatory cytokine responses, whereas afternoon surgery was associated with higher oxidative stress and antioxidant capacity. These findings suggest that surgical timing may influence acute postoperative inflammatory, oxidative, and immune responses in cattle and may therefore be relevant to postoperative management and animal welfare.