Thyroid hormone dynamics of Tharparkar and Sahiwal cattle during induced heat stress.

Thyroid hormones and Cortisol level are the essential biomarkers in the assessment of stress condition. This study was done to estimate the metabolic hormonal profile of Tharparkar and Sahiwal during heat stress condition. The experiment was conducted on two groups consisting of Tharparkar and Sahiwal animals (5 in each group) and the experimental period comprised a 7-day acclimatization period, a heat exposure period of 21 days at control (25 °C), moderate (35 °C) and severe (42 °C) heat stress within a 9-10-day recovery period between each exposure. The hormonal concentrations of T, T and cortisol were determined in serum. The serum concentration of Thyroxine (T) and tri-iodothyronine (T) decreases whereas cortisol level increases in both the breeds when subjected to heat stress. However, the serum level of T was significantly (p < 0.05) more declined in Sahiwal as compared to Tharparkar but there was no significant difference found between the two breeds in serum T levels. The cortisol levels were elevated in both breeds during heat stress but significantly (p < 0.05) more elevated in the Sahiwal. Hence, observations of these hormonal profiles suggest a better thermo-adaptability in Tharparkar as compared to Sahiwal.