USE OF HISTRELIN SUBDOSES AT THE BAI-HUI ACUPUNCTURE POINT AS A STRATEGY FOR OVULATION INDUCTION IN MARES

INTRODUCTION: Controlling the timing of ovulation is essential for the efficiency of equine reproduction programs, especially artificial insemination, as it allows better use of semen and improved organization of reproductive management. Histrelin is a synthetic GnRH analogue used to induce ovulation, whereas pharmacopuncture enables the administration of reduced drug doses at acupuncture points. AIMS: To evaluate the efficacy of administering 25 μg of histrelin at the Bai-hui acupoint to induce ovulation in mares and to compare its response with different doses administered intramuscularly, saline solution applied at the same acupoint, and no intervention. MATERIALS AND METHODS: Eleven healthy mares from the herd of the Gralha Azul Experimental Farm at PUCPR were initially selected. Two were excluded due to irregular cyclicity, resulting in nine animals. Each mare underwent six protocols: 250, 75, and 25 μg of histrelin administered intramuscularly; no intervention; 1 mL of saline solution administered at Bai-hui; and 25 μg of histrelin administered at Bai-hui. Mares were included when they presented a follicle measuring between 35 and 38 mm, uterine edema score 3, and cervical relaxation. Ovulation was monitored by transrectal ultrasonography and was considered successfully induced when it occurred between 24 and 48 hours after treatment. The protocols were randomized, except for the first cycle, in which protocol 1 was used for all the mares, and post-induction evaluations were performed blindly. Ovulation rates were compared using Fisher’s test, with a significance level of 5%. RESULTS: The intramuscular protocols showed the same ovulation rate within the expected period, corresponding to 88.89%. The no-intervention protocol resulted in a rate of 44.4%, whereas saline solution administered at Bai-hui resulted in 66.67%. The administration of 25 μg of histrelin at Bai-hui resulted in 100% of ovulations occurring between 24 and 48 hours and showed the lowest standard deviation among the treatments, at 4.22 hours. A significant difference was observed only between the no-intervention protocol and the protocol involving histrelin administration at Bai-hui. FINAL CONSIDERATIONS: The 25 μg dose of histrelin was effective when administered both intramuscularly and at the Bai-hui acupoint. The protocol involving administration at the acupoint showed greater uniformity in ovulation timing, although it did not differ significantly from the other histrelin-containing treatments. These results demonstrate the potential of reducing the hormonal dose and support further studies involving a larger number of animals.

KEYWORDS: Acupuncture; Well-being; Horse; Equine; Complementary medicine.