LAUSR

Environmental stressors such as temperature, humidity, rainfall, photoperiod, etc. under tropical conditions are some of the important limiting factors for optimum expression of production and reproduction in dairy cows. The present study evaluated changes in cardinal physiological responses, heat tolerance indices, and milk yield in Jersey crossbred cows due to abiotic stress. Climograph was developed using daily maximum and minimum temperatures, humidity, and rainfall at livestock farm over a period of 15 years. Seasons significantly (P < 0.01) influenced cardinal physiological responses and thermal adaptability of Jersey crossbred cows. Diurnal environmental variations between morning and afternoon of the shed caused increase in body temperature, pulse, and respiration rate by 0.59–0.91%, 4.95–7.18%, and 9.73–32.37%, respectively. Thermal adaptability of cows showed significant (P < 0.01) higher deviations from perfect state of adaptability during summer, monsoon, and post-monsoon as compared to winter and spring seasons. The responsiveness and ranking of cows were dissimilar among 3 heat tolerance indices, viz., Iberia heat tolerance index, Benezara’s coefficient of adaptability, and Dairy Search Index (DSI). Enhanced respiration rate was the most important observable bio-indicator to poor thermal adaptability. Good thermo-tolerant cows had 8.86% higher (P < 0.05) monthly milk yield per cow than poorly adapted ones. Findings of this study suggest that deviations in cardinal physiological responses across the seasons are very reliable and simple estimates for evaluating levels of thermo-tolerance in crossbred cows.