The effect of prolonged heat stress on haematological parameters of Holstein cows

Prolonged heat stress poses a significant challenge to the productivity and health of Holstein cows due to their heightened sensitivity to high temperatures and intensive metabolism. The purpose of this study was to investigate changes in haematological and immunobiological parameters in Holstein cows under prolonged heat stress conditions. The study included 18 cows in their second and third lactations, which were divided into two groups: one exposed to hyperthermia during the summer (August) (HYP, n = 8), and the other maintained under thermally comfortable conditions in the autumn (October), serving as the control group (CON, n = 10). Blood analysis was performed using methods commonly accepted in clinical veterinary practice. The results revealed significant reductions in red blood cell count (by 14.5%), haemoglobin level (by 11%), and haematocrit (by 8.4%) in HYP cows compared to CON (P < 0.05), indicating disruptions in erythropoiesis or reduced erythrocyte lifespan. Concurrently, an increase in mean corpuscular volume (by 8.9%) and platelet count (by 53%), alongside a decrease in mean platelet volume (by 20%), suggested adaptive metabolic and coagulation responses of the organism. A 48% decrease in serum lysozyme activity and a 36% increase in circulating immune complex levels indicated suppression of innate immunity and activation of compensatory immune defence mechanisms. The practical significance of the study lies in identifying potential biological markers for monitoring and managing heat stress, which could improve the health, productivity, and welfare of dairy cows