Effects of a combined nutritional and cooling strategy on productivity and immune responses in heat-stressed Holstein dairy cows

This study investigated the heat stress mitigation effects of combining nutritional (heat-treated fermented soybean meal, HFSBM) and cooling interventions in dairy cows.Twelve Holstein cows were assigned to a control (CON; n = 6) or heat stress-mitigating treatment (HSMT; n = 6) group for 2 weeks under heat stress condition (temperature humidity index [THI] = 80.60).CON received a standard total mixed ration (TMR), while HSMT received TMR with 0.1% HFSBM and was exposed to a cooling system (fans and misting).Productivity, physiological parameters, and gene expression in peripheral blood mononuclear cells (PBMCs) were evaluated.No significant differences were observed in milk yield, milk composition, respiration rate, or rectal temperature.However, HSMT significantly reduced mRNA expression of pro-inflammatory cytokines IL-1β (p = 0.038) and IFN-γ (p = 0.021) in PBMCs.mRNA expression of the cellular stress marker HSP90 (p = 0.028) also significantly decreased in the HSMT group.Furthermore, HSMT significantly increased mRNA expression of antioxidant enzymes SOD1 (p = 0.003) and CAT (p = 0.002).Although the 2-week combined treatment did not affect production or physiological indices, it effectively alleviated stress responses at the cellular and molecular levels.These findings suggest that combining cooling and HFSBM supplementation effectively enhances immune stability and health by reducing inflammation and cellular stress in heat-stressed dairy cows.