Influence of the dopamine antagonist domperidone on the vernal transition in seasonally anoestrous mares.

This study aimed to establish the impacts of long-term domperidone use, a dopamine antagonist, on ovulation, endocrine profiles, and follicular development in anoestrous mares.

Methods

• Researchers studied 16 anoestrous mares kept under natural light and temperature conditions.
• The team administered domperidone daily to eight of these mares from January 15 to the first ovulation of the year.

Results

• Researchers observed a significant increase in the number and size of follicles 20 mm or more in diameter in the treated mares compared to the control group from day 14 of treatment.
• First ovulation was significantly earlier in domperidone-treated mares than in untreated ones, with an average time difference of 78 days.
• All eight mares treated with domperidone ovulated during the treatment period.
• The average time from the beginning of treatment to the first ovulation was 27 days (ranging between 15-55 days).
• Among these, six treated mares experienced regular cycles after the first ovulation, while two experienced a lengthy interval before the second ovulation (an average of 67 days).
• The levels of prolactin in the blood were significantly higher in domperidone-treated mares than in control mares on day 7 of treatment.
• By the 28th day of treatment, the concentrations of LH and oestrogen conjugates were significantly higher in the group that was administered domperidone than in the control mares. However, no differences in FSH concentrations were observed.

Implications

• The domperidone or prolactin level raises may be directly influencing the ovary, given the significant increases in follicular development and the concentrations of oestrogen conjugates without matching increments in FSH concentrations.
• This study illustrates how domperidone can assist in advancing the vernal transition of anoestrous mares, which could hold implications for breeding timing and management.