Fluctuations of Estradiol and Progesterone in Phan Rang Sheep During the Estrous Cycle

Abstract

This study was conducted to characterize the temporal variations in estradiol and progesterone concentrations throughout the estrous cycle of Phan Rang ewes raised under semi-intensive conditions at the Binh Duong Center for Large Ruminant Research and Development, currently Ben Cat Livestock Research Station, Institute of Animal and Veterinary Sciences for Southern Vietnam. A total of 42 ewes exhibiting clear estrous signs were selected, and blood samples were collected daily between 07:00 and 08:00 for 20 consecutive days to monitor endocrine fluctuations. Serum samples were centrifuged and analyzed for estradiol and progesterone concentrations using an electrochemiluminescence immunoassay on the Cobas E601 automated system to ensure high analytical sensitivity and precision. The results indicated that both age groups studied (12–24 months and >24–36 months) exhibited typical hormonal fluctuation patterns characteristic of the estrous cycle. Estradiol concentrations peaked on day 2, with mean values of 7.46 ± 0.65 pg/mL and 8.73 ± 0.61 pg/mL in the respective age groups, and reached their lowest levels on day 11. In contrast, progesterone concentrations were lowest on day 1, followed by a progressive increase that culminated in peak values on day 12, recorded as 8.31 ± 1.21 ng/mL in the 12–24-month group and 8.96 ± 0.93 ng/mL in the >24–36-month group. These findings provide essential physiological evidence on the estrous cycle of Phan Rang ewes, supporting the determination of optimal breeding timing and enhancing reproductive management under semi-intensive production systems. Moreover, the hormonal profiles generated in this study could be used as a reliable reference for future research and for reproductive management strategies aimed at improving the reproductive performance of Phan Rang sheep.