Impact of acute heat stress on hematological and biochemical profiles in Brown Swiss cows

Heat stress (HS) is a critical environmental factor that disrupts dairy cows' physiological and metabolic balance, leading to impaired productivity, immune suppression, and oxidative stress. The Brown Swiss breed is known for its relatively higher thermotolerance, yet its hematological and biochemical responses to acute HS remain poorly understood. This study aimed to evaluate the impact of acute heat stress on the hematological and biochemical parameters of Brown Swiss dairy cows, identifying key physiological adaptations and potential biomarkers for stress assessment. The experiment involved 16 Brown Swiss cows in their second lactation, divided into a heat-stressed group (HYP, n = 8) and a control group (CON, n = 8). Heat stress conditions were characterized by a temperature-humidity index (THI) of 77.6 for five consecutive days. Hematological and biochemical analyses were conducted using an automated haematology analyzer and biochemical assays to assess oxygen transport capacity, metabolic adaptations, and immune responses. The results demonstrated significant changes in key blood parameters due to acute HS. Haemoglobin concentration decreased by 8.8% (P < 0.05), while platelet count and leukocyte levels were reduced by 30.2 % and 25.1 %, respectively (P < 0.05), indicating hematopoietic and immune alterations. Biochemical findings showed a 21.8 % increase in albumin concentration (P < 0.05), along with a 77.5 % rise in blood urea nitrogen (P < 0.05), suggesting enhanced protein catabolism. Additionally, total lipoprotein levels increased by 56.3 % (P < 0.05), and β-carotene concentration rose by 87.1 % (P < 0.05), reflecting metabolic shifts and oxidative stress adaptation. Thus, acute HS induces significant hematological and biochemical alterations in Brown Swiss cows, affecting oxygen transport, immune function, and metabolic regulation. The findings highlight the physiological trade-offs necessary for thermoregulation, emphasizing the need for targeted nutritional and environmental strategies to enhance heat stress resilience in dairy cattle. Further research is warranted to explore long-term adaptations and develop practical mitigation approaches.