Cortisol and Postpartum Luteal Function in Cattle

The present study investigated serum cortisol in response to postpartum ovarian resumption and luteal func-tion. Postpartum ovarian resumption was detected based on a rise in progesterone (P4) concentrations dur-ing 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 P4 in se-rum (P4 > 1.0 ng/mL), 11 of the 22 cows resumed the ovarian activity within three weeks after calving (ovar-ian resumption cows). No effect of THI was found during the postpartum period of study on the concentra-tions of P4, cortisol and cholesterol in the ovarian resumption or non-ovarian resumption group. In the for-mer, 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 P4 (r=0.289, P < 0.05) but showed no correlation with cortisol. In addition, cortisol showed a significant correlation with P4 (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.