Periovulatory changes in ovarian temperature in ewes

Area of Science:

• Reproductive endocrinology
• Animal physiology
• Thermoregulation

Background:

• Estrus induction in ewes typically involves progesterone withdrawal.
• Monitoring ovarian and aortic temperatures can provide insights into reproductive events.
• Luteinizing hormone (LH) surge is a key indicator of ovulation.

Purpose of the Study:

• To investigate the relationship between ovarian temperature fluctuations and estrus/ovulation in ewes.
• To explore the role of estradiol in modulating ovarian blood flow and temperature.
• To determine if pre-ovulatory temperature changes can predict ovulation.

Main Methods:

• Implantation of thermistors in ewes to record ovarian and aortic temperatures for 72 hours.
• Hourly measurement of serum LH levels during estrus.
• Laparotomy for ovarian examination to confirm ovulation.
• Calculation of ovarian temperature relative to aortic temperature to control for basal body temperature variations.

Main Results:

• Four out of six ewes exhibited estrus behavior, an LH surge, and a fresh corpus luteum.
• In ovulating ewes, ovarian temperatures decreased by ~0.15°C, reaching a minimum before the LH surge.
• Ovulating ovaries had lower mean temperatures and an earlier pre-ovulatory decrease compared to non-ovulating ovaries.

Conclusions:

• The observed pre-ovulatory ovarian temperature decrease in ovulating ewes supports the hypothesis that estradiol increases ovarian blood flow.
• Ovarian estradiol may act as a thermoregulatory factor, potentially influencing ovulation.
• Proximity of the uterine mass might contribute to a heat-sink effect on ovarian temperature.