Thermal Stress Influence and Seasonal Pattern of Ovarian Follicular Growth Assessed through Ultrasonography in Sunandhini Cows under A Humid Tropical Climate

The impact of thermal stress (TS) on reproductive processes starts early and persists more extended than the influence on other physiological manifestations. Since the cyclical reproductive activity begins with the growth of ovarian follicles, the present study focused on the effect of TS and its seasonal variations on the growth of ovarian follicles in ‘Sunandhini’ cows reared under the tropical climate. The year-round study was performed on 60 postpartum cows between days 28 to 91, involving eight cows at a time. The cows were replaced sequentially so that the study animals were of almost similar postpartum period throughout the year and formed a continuously changing study group. The ovarian follicular activity of each cow was monitored (nine to ten times) at weekly intervals using B mode ultrasonography. Serum samples collected during the scanning were subjected to ELISA for heat shock protein (HSP) 70 and Cortisol. A comparison of the follicle types, stress indicators, and weather parameters to assess their correlations and seasonal pattern using SPSS software. The maximum temperature of the locality was around 33ºC without significant variation between seasons. Further, the extended rainy season caused moderate to high (66 to 85 %) relative humidity (RH), contributing to a temperature-humidity index (THI) exceeding 78 and putting the animals under moderate to severe TS throughout the year. HSP 70 level showed significant (P