Impact of seasonal variation on endocrine profile during an estrous cycle in Jersey crossbred dairy cows

The objective of the study was to investigate the influence of season viz., summer, winter, and isothermic (spring and autumn season), on endocrine profile in dairy cows. The daily temperature-humidity index (THI) was recorded using a dry and wet-bulb thermometer to envisage its variation among different seasons. For analysis of endocrine profile, blood samples were collected from thirty dairy cows (n=10 in each season) at 5 -day interval i.e. day 0 (day of estrus) to day 20, of the estrous cycle for ELISA based estimation of estradiol-170, progesterone, and cortisol. In results, the THI varied significantly (p<0.01) in different seasons with maximum THI in the summer (72.54), followed by the isothermic (64.7) and lowest in the winter season (54.12). Among the endocrine profile, the plasma cortisol levels had a significant variation (p<0.05) in different seasons with increased levels in the winter followed by the summer season, however, differences were non-significant (p>0.05) in plasma progesterone and estradiol-170. In summary, seasonal variation barely led to significant changes in the reproductive hormones (estrogen and progesterone) but alleviated cortisol levels during summer and winter season had been suggestive of stress and could result in reduced fertility.