Hormonal Agent (Systemic Drug)
- Buserelin is a synthetic gonadotropin-releasing hormone (GnRH) analogue that is designed to alter hormone levels.
- Typically employed in order to induce ovulation in cyclic mares.
- Acts as natural LH/FSH releasing hormone produced in the hypothalamus. It causes simultaneous release of luteinising hormone (LH) and follicle stimulating hormone (FSH) from the pituitary.1
Recent studies have shown that buserelin:
- Is at least 50 – 60 times more effective than Gonadorelin, the alternative GnRH active (as measured in FSH and LH response).
- Stimulates high production of LH for efficient induction of ovulation and better support of corpus luteum formation and early luteal function.
Recently reported trials demonstrate that treating mares with the gonadotropin-releasing hormone analog buserelin 9 or 10 days after ovulation increases pregnancy rates.
Early embryonic loss is a major cause of sub-fertility in mares. Progesterone produced in the ovary by the corpus luteum maintains the early pregnancy. The embryo must signal its presence and ensure the corpus luteum is maintained in order to survive the first few weeks of pregnancy. In other species, luteal function in pregnant animals starts to diverge from that of non-pregnant animals between 11 and 14 days after ovulation. It is therefore, considered to be a critical time for the maintenance of the pregnancy. Treatment with 20µg or 40µg buserelin 9 or 10 days after ovulation significantly increased the overall pregnancy rate by up to 10% in mares.2
In humans, for carcinoma, prostatic (treatment), buserelin is indicated for the palliative treatment of advanced prostatic cancer (stage D), especially as an alternative to orchiectomy or estrogen administration.5
Commonly employed in order to induce ovulation in cyclic mares.
Buserelin is a synthetic form of GnRH and stimulates the production and release of FSH and LH from the anterior pituitary. Secretion of endogenous GnRH from the hypothalamus is thought to be controlled by several factors, including circulating sex hormones. Buserelin causes a surge-like release of FSH and LH after a single injection.
In one study, 22 heavy draft mares were divided into a buserelin-treated group (n=8) and a control group (n=14). Mares were given an intramuscular injection of 40 µg buserelin when they presented signs of estrus to a teaser stallion, had ≥45 mm diameter follicles, and presented decreased uterine edema compared with the previous examination. The follicles and uterus were monitored using transrectal ultrasound imaging and measurement of blood levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone, and estradiol-17β. The ovulation rates within 48 hr was significantly higher in the treated group (100%, 8/8) than in the control group (57.1%, 8/14; P=0.051).
The mean ± SEM time before confirmation of ovulation was 29 ± 9 hr for the treated group and 59 ± 7 hr for the control group. There were no significant differences in mating frequency, double ovulation rate, or fertility rate between the two groups. One to two days after administering buserelin, LH and FSH temporarily increased, and in the control group, LH was high during ovulation, whereas FSH temporarily increased with the growth of the follicle. These results indicate that a single injection of 40 µg buserelin when follicles are at least 45 mm in diameter and uterine edema is decreased is effective for inducing ovulation.3
Contraindications / Precautions:
Adverse effects, including injection site reactions, were reported at the same rate as placebo in manufacturer field studies. Synthetically prepared buserelin should not cause any hypersensitivity reactions. This may not be the case with pituitary-obtained LH preparations or hCG.4
Horses (mares): 20µg or 40µg buserelin 9 or 10 days after ovulation.
1Nawito et al. (1977); Reeves et al. (1980); Loumaye et al. (1982); Chenault et al. (1990). msd-animal-health.co.nz.
2J R Newcombe, T A Martinez and A R Peters. The effect of the gonadotropin-releasing hormone analog, buserelin, on pregnancy rates in horse and pony mares. Theriogenology, (2001) 55, 1619-1631.
3Miki, W., Oniyama, H., et. al. Effects of a single use of the GnRH analog buserelin on the induction of ovulation and endocrine profiles in heavy draft mares. J Equine Sci. 2016; 27(4): 149–156.
4Plumb's Veterinary Drugs.