Follicle stimulating hormone, luteinising hormone and progesterone concentrations in the blood of thoroughbred mares exhibiting single and twin ovulations.

This study aimed to understand the relationship between levels of follicle stimulating hormone, luteinising hormone, and progesterone, and their impact on single or twin ovulations, in thoroughbred mares. The study found no simple relationship but did discover that progesterone levels were higher after twin ovulations, suggesting that the cause of twin ovulation might be found in the ovarian system involved in follicular development and ovulation.

Research Objective and Methodology

The research focused on examining the concentrations of follicle stimulating hormone (FSH), luteinising hormone (LH) and progesterone (P4) in the blood samples taken from the thoroughbred mares throughout the oestrous cycle. This was done to:

• Investigate any potential relationship between circulating gonadotropin (FSH and LH) levels and the ovulation rate in mares.
• Observe changes in progesterone concentration during dioestrus – a phase in the estrous cycle – after single versus twin ovulations.

Key Findings

The hormone profiles that resulted from the study made several things clear:

• There does not exist a straightforward relationship between the levels of circulating gonadotropins and the subsequent rate of ovulation in mares. This means that gonadotropin levels do not directly influence whether a mare will have single or twin ovulations.
• Progesterone concentration in plasma was higher during dioestrus when the mare had experienced a twin ovulation compared to a single ovulation. Dioestrus is a period of sexual inactivity after ovulation, in the estrous cycle.

Implications of the Study

This study suggests that the phenomenon of twin ovulation in some mares may be due to variables present at the ovarian part of the pituitary-ovarian axis. The pituitary-ovarian axis refers to a complex interaction between the pituitary gland and the ovaries which regulates:

• Follicular development – the growth and maturation of the egg in the ovary.
• Ovulation – the release of the egg from the ovary.

This means that the phenomenon of twin ovulation might be more influenced by factors at the ovarian level rather than just hormone levels. This insight opens the door to further research aiming to uncover the specific ovarian factors influencing ovulation rate in mares.