Abstract
The present study investigated serum cortisol in response to postpartum ovarian resumption and luteal function. Postpartum ovarian resumption was detected based on a rise in progesterone (P-4) concentrations during three weeks after calving. Twenty two Holstein cows in a semi- closed dairy farm in Qena city, Egypt were used. The study was carried out from late March to early June; the period characterized by a good temperature humidity index (THI) and absence of heat stress. According to the concentrations of P-4 in serum (P-4 > 1.0 ng/mL), 11 of the 22 cows resumed the ovarian activity within three weeks after calving (ovarian resumption cows). No effect of THI was found during the postpartum period of study on the concentrations of P-4, cortisol and cholesterol in the ovarian resumption or non- ovarian resumption group. In the former, cholesterol showed a significant correlation with both P4 (r= 0.405, P< 0.05) and cortisol (r= 0.393, P< 0.05). However, in the latter, cholesterol had a significant correlation with P-4 (r= 0.289, P< 0.05) but showed no correlation with cortisol. In addition, cortisol showed a significant correlation with P-4 (r= 0.329, P< 0.05) in the ovarian resumption group but showed no correlations in the non- resumption group. Our study suggests that cortisol plays a role in the function of corpus luteum and maintenance of luteal life span during this period.