Preliminary studies on the use of an oral progestogen to induce oestrus and ovulation in seasonally anoestrous Thoroughbred mares.

This study examined the effects of giving Thoroughbred mares a specific oral hormone treatment to trigger estrus and ovulation during periods when they are seasonally non-reproductive. The research found that the treatment was successful in inducing these conditions in a large percentage of the mares tested.

Research Methodology

• The researchers used 61 Thoroughbred mares for this study, all of which were either barren, maiden (never given birth), or lactating and showing signs of deep anoestrus (lack of reproductive activity), shallow anoestrus, prolonged spring estrus (periods of sexual receptivity and ovulation), or lactation anoestrus.
• Each of these mares was given 30 mg of allyl trenbolone, commercially known as Regumate, daily for 10 to 15 days.

Research Findings

• After the treatment, 54 mares (88 per cent) began displaying estrous behavior within 8 days, and 51 mares (84 per cent) ovulated within 18 days of the last dosage. This demonstrates that the progesterone derivative was successful in stimulating reproductive behavior in a majority of the test subjects.
• However, the response rate was lowest in mares that were in deep anoestrus, indicating that the effectiveness of the treatment may be reduced during periods of prolonged non-reproductive activity.
• Of the 38 treated mares that were bred during the induced estrus, 21 (55 per cent) became pregnant. This suggests that the Regumate treatment not only induced estrus and ovulation but also increased the chances of successful conception.

Implications of the Study

• The researchers discuss the usefulness of this progesterone withdrawal therapy as a means to kick-start the breeding season in Thoroughbred mares. The efficiency with which the treatment induced estrus and ovulation, as well as the significant conception rate, indicate the potential for this treatment to be used to manage the Thoroughbred mare’s reproductive cycle.
• The potential for this method to increase the predictability and efficiency of Thoroughbred breeding programs is significant, though the decreased effectiveness in mares in deep anoestrus suggests some limitations.