Thermal Stress Associated Serum Factors and the Influence of Weather Parameters in Crossbred Dairy Cows Under Humid Tropics

Abstract

Assessment of the level of thermal stress (TS) in animals exposed to adverse weather helps to formulate and implement alleviation measures. Present study was to identify the presence and seasonal pattern of serum factors to be used as biological indicators for early detection of TS in animals. The year-round study involved eight cows each at a time, belonging 28 to 91 days postpartum, and replaced two cows every month. Analyzed the levels of Heat shock protein 70 (HSP 70) and cortisol in serum samples collected at weekly intervals and assessed the seasonal pattern and correlation with weather parameters. While minimum temperature (MnT) of the region varied significantly (P<0.01) between seasons (lowest mean 22.09±1.19 ºC), maximum temperature (MxT) was consistently high across seasons (yearly mean 33.64±0.77 ºC). Moderate to high (66 to 85 %) relative humidity (RH) was prevalent year-round, mainly contributed by the extended rainy season. Temperature-humidity index (THI) of the locality exceeded 78, exposing the animals to moderate to severe TS throughout the year. HSP 70 levels varied significantly (P<0.01) between seasons, with a significant hike (6.24±0.51 ng/mL) during summer (THI 83.20±0.53) and lesser elevation during other seasons of moderate THI, indicating its association with TS. Cortisol levels varied significantly (P<0.01) between seasons, however there was no significant correlation with THI and other weather parameters. To conclude, while cortisol forms a general indicator of physiological stress, HSP 70 appears more specific to TS, and its usefulness for early detection of TS needs further studies.