Impact of heat stress on physio-biochemical parameters during early lactation of crossbred dairy cattle

The thermal stress adversely affects crossbred dairy cattle production, especially in a hot, humid tropical state like Kerala. So, assessment of the intensity of stress and its relationship with the physiological alterations are crucial in adopting proper mitigation strategies to attain sustainable production. Hence this study was formulated to investigate the impact of heat stress on physio-biochemical parameters during early lactation of crossbred dairy cattle. The study comprised two sets of animals: six animals calved in month of December (control, season I) and six animals calved in the month of March (heat stressed,season II). Significant elevations (p < 0.05) in all the climatic and physiological parameters were noted in the second season. The heat stress did not result in significant differences (p > 0.05)in various blood and serum biochemical parameters such as potassium (K+), bicarbonate (HCO3(-)), calcium (Ca2(+)), phosphorus (P), Globulin, total erythrocyte count (TEC), Total leucocyte count (TLC), haemoglobin (Hb), the volume of packed red cells (VPRC), aspartate aminotransferase (AST), glucose, beta hydroxyl butyrate (BHB), non-esterified fatty acid (NEFA) and triglyceride (TG).Significant differences (p < 0.05) were noted in sodium (Na+) on day zero postpartum and chloride (Cl-)on day 45 postpartum. Furthermore, there was a significant decrease (P < 0.05) in partial pressure of carbon dioxide (PCO2), gamma-glutamyl transferase (GGT), total protein, albumin, triiodothyronine (T-3) and thyroxine (T-4) during heat stressed period while cortisol and partial pressure of oxygen (PO2) levels increased. This study also revealed a highly significant reduction (p < 0.01) in milk yield, indicating the animals maintained their positive energy balance at the expense of milk production during the study period.