Levels of luteinizing hormone and progesterone during the estrous cycle and early pregnancy in mares.

The research abstract details a study on hormonal fluctuations, specifically luteinizing hormone and progesterone, in mares during their estrous cycle and early pregnancy, with blood samples taken daily. The results demonstrate specific cyclical hormonal changes in line with different phases of the estrous cycle and show that neither palpation nor breeding significantly affected progesterone levels during a specific 12-day period after estrus.

Methodology

• The researchers collected daily blood samples from the jugular veins of 16 mares throughout their estrous cycle. Through this, they aimed to observe the hormonal fluctuation in the mares, focusing specifically on levels of luteinizing hormone (LH) and progesterone.
• The mares were divided into groups: twelve were bred to fertile stallions, with subsets of four each subjected to daily palpation throughout the estrous cycle, during estrus, and no palpation. The remaining four mares were neither palpated nor bred, and their blood samples were collected at 6-hour intervals during estrus.
• The blood collected from all mares was processed to extract serum via centrifugation, which was then analyzed through a technique called radioimmunoassay to determine the levels of LH and progesterone.

Findings

• The researchers noted an increase in LH levels in the serum beginning at the onset of estrus, peaking at about 85 ± 18 ng/ml approximately 24 hours before the end of estrus. The baseline LH level during diestrus was maintained between 10 and 15 ng/ml.
• Progesterone levels, on the other hand, remained low (<1 ng/ml) until just before the LH peak, beginning to rise prior to the onset of diestrus and reaching a plateau (4–10 ng/ml) between the 5th and 14th days of diestrus.
• An important observation made was that the progesterone levels during the twelve-day period following estrus remained unaffected (P<0.05) by either palpation or breeding.

Conclusions

• As a result of this study, there were specific identified patterns of hormonal changes throughout the estrous cycle. Particularly noteworthy was the gradual increase in LH levels beginning at the onset of estrus, peaking approximately 24 hours before its end, and the rise in progesterone levels just before the onset of diestrus.
• This research can be considered significant because it shows that the hormone levels of mares, including those bred to fertile stallions, are not significantly affected by palpation or breeding, which is useful knowledge for equine reproduction management.