Practical Application of Progesterone in Reproduction

INTRODUCTION

Determination of progesterone values is of great interest in the daily clinic, both with in-home qualitative tests or with semi-quantitative tests at a reference laboratory 1

PHYSIOLOGY OF PROGESTERONE

During the estrus phase, there is a progressive decrease in the levels of estradiol in bitches, which may affect the onset of the LH surge, that takes place at the onset of estrus and then, 48 h later will trigger ovulation 2.3 . While some studies have concluded that the LH surge occurs on the first day of estrous behavior, others have found no correlation between the LH surge and the behavior of acceptance of the male 2 .

According to various studies, the duration of the LH surge ranges from 24 to 96 hours 2 . Ovulation occurs within 2-3 days after the LH surge. The bitch ovulates primary oocytes, and fertilization does not end until 48-72 h after ovulation, since primary oocytes must undergo a second meiosis to become fertile secondary oocytes 2

Progesterone levels begin to rise at about the same time that the LH peak, an event known as preovulatory progesterone rise, while estrogens are decreasing, thereby decreasing the vaginal and vulvar edema. Progesterone levels during LH peak are between 0.8 and 3 ng/ml; at the time 123 of ovulation, progesterone values are between 4.0 and 10 ng/ml ; and during the fertile period they are between 4.0 and 20 ng/ml 1 .

Ovulation is not always related to estrous behavior, and there may even be variations depending on the breed. Moreover, there are bitches that do not allow mating during ovulation 2 .

Later, progesterone reaches its highest levels, around 15 and 90 ng/ml, about 15 and 30 days after the LH surge. After day 30, progesterone concentrations gradually decrease for 5-6 more weeks. The decline of progesterone levels below 2 ng/ml occurs 24-36 h before delivery, being a necessary condition for the normal delivery.  […]