Adaptive Capability as Indicated by Redox Status and Endocrine Responses in Crossbred Cattle Exposed to Thermal Stress

A series of studies were conducted to assess the effect of increasing environmental temperatures on redox status and endocrine responses in crossbred cattle under simulated conditions. In present study four non-lactating crossbred cattle were exposed to 25, 30, 35 and 40°C temperature with relative humidity of 40-50% in psychrometric chamber for 5 hours/day from 10:00 to 15:00 hours for 21 days. The physiological responses, feed and water intake were recorded and blood samples were collected at 15:00 hours on day 1, 6, 11, 16 and 21 of the experiment. Blood serum was harvested to estimate superoxide dismutase activity (SOD), reactive oxygen species (ROS), tri-iodothyronine (T3), thyroxine (T4) and cortisol concentration. The temperature exposures of 25 and 30°C did not affect physiological responses, feed intake, water intake, T3, T4, cortisol concentration and SOD activity in serum. The dry matter intake (DMI)/day decreased significantly (p<0.05) whereas water intake, respiratory rate and rectal temperature increased progressively at 35 and 40°C as compared to 25 and 30°C temperature exposure. The serum ROS level increased progressively with increase in exposure temperature and a corresponding increase in serum SOD activity was also observed up to a temperature exposure of 35°C however, SOD activity declined at 40°C exposure. Serum T4 concentration decreased whereas cortisol level increased significantly at 35 and 40°C exposure as compared to 25 and 30°C temperature exposure. It can be concluded from the present study that the crossbred animals can readily adapt to a temperature exposure of 25 and 30°C and can acclimatize up to 35°C with compensatory physiological, biochemical and endocrine changes but fail to do so at the temperature exposure of 40°C.