Plasma LH levels in the mare during the oestrous cycle

Area of Science:

• Veterinary Science
• Reproductive Biology
• Endocrinology

Background:

• Understanding equine reproductive cycles is crucial for breeding management.
• Hormonal fluctuations, particularly Luteinizing Hormone (LH), play a key role in ovulation and cycle regulation.
• Previous studies on LH patterns in mares are limited, especially concerning its post-ovulatory behavior.

Purpose of the Study:

• To characterize the plasma Luteinizing Hormone (LH) profiles throughout the estrous cycle in mares.
• To investigate the duration and pattern of LH concentrations, particularly after ovulation.
• To explore the potential relationship between LH levels and the incidence of multiple ovulations in mares.

Main Methods:

• Plasma LH levels were quantified using a heterologous radioimmunoassay with purified equine LH as the standard.
• Regular blood samples were collected from eleven mares over twenty-six estrous cycles (10 weeks).
• Cycle length, time to ovulation from detected heat, and LH concentration changes were analyzed.

Main Results:

• Mean estrous cycle length was 20.5 ± 3.1 days, with ovulation occurring 4.3 ± 1.6 days after heat onset.
• LH levels remained low from Day 5 to 16, then gradually increased post-ovulation, exceeding pre-ovulatory levels.
• A significant decrease in LH was observed 3 days post-ovulation, with a subsequent decline exhibiting a half-life of 1.8 days.

Conclusions:

• The plasma LH pattern in mares is distinct, characterized by a prolonged elevation post-ovulation.
• This extended persistence of high LH concentrations is attributed to a long half-life of endogenous LH.
• The unique LH profile in mares may contribute to the observed frequency of multiple ovulations within a single estrous cycle.