Changes in cortisol levels during estrous cycle and peripartum period of native Egyptian cattle

Cortisol levels were determined [RIA] in the plasma of five mature cyclic Egyptian heifer cows during green and dry seasons of the year as well as in the peripartum period of five cows till the first postpartum estrus. Cortisol level increased [P <0.01] at the day of estrus with no obvious changes between the green and dry seasons. The slope of cortisol increased [P <0.01] with the approach of calving and insignificantly fluctuated during the postpartum period