Crossbred cows respond differently from Holstein Frisian and Bos Indicus to heat stress under various climatic conditions

The ability to adapt to environment is of great importance to all living things.Heat stress response was determined in dairy cows,9 each from Holstein Frisian (HF), Crossbred-50% (HF × Sahiwal) and Bos Indicus (Sahiwal and Achai). Cows were sampled at environmental temperature 18, 32 and 42 °C in February, April and June, respectively. The physiological parameters recorded were rectal temperature (RT), respiration rate (RR) and pulse rate (PR) whereas biochemical parameters determined from blood serum were glucose, cortisol and Heat shock protein-70 (HSP-70). Thermal stress increased all physiological parameterssignificantly (P < 0.001). Holstein Frisian manifested maximumincrease in RT, RR and PR (3.33, 209.50 and 59.41%) than crossbred (0.59, 40.22 and 22.0%), Sahiwal (0.78, 42.54 and 34.31%) and Achai (0.78, 39.22 and 33.85%) respectively (P < 0.001).Thermal stress increased biochemical changes significantly (P < 0.001). The increase in serum glucose, cortisol and HSP-70 concentrations wasmaximum in HF (43.44, 119.06 and72.11%) andcrossbred (38.66, 159.61 and79.12%) and minimum inAchai (34.93, 123.59 and52.53%) and Sahiwal (27.26, 117.22 and65.41%)respectively (P< 0.01). Holstein Frisian appeared as the most heat sensitive breed exhibiting changes at 32 °C i.e. 5 °C higher than 27 °C (upper critical temperature, UCT). Sahiwal and Achai were the most heat tolerant breeds manifesting changes at 42 °C i.e. 15°C higher than UCT. The crossbred cows responded differently to heat stress and showed biochemical changesat 32 °C like HF and physiological changes at 42 °C like Bos Indicus. It appears that crossbred cows acquire some genes for low physiological response to thermal stress from Bos Indicus cows and acclimatization to the tropical conditions of Pakistan.Therefore, further study is needed on acquisition of genes from Bos Indicus for low physiological response in crossbred cows