title: Effects of a single use of the GnRH analog buserelin on the induction of ovulation and endocrine profiles in heavy draft mares.
abstract: We observed structural changes in the follicles and uterus of heavy draft mares during estrus and examined the effect of a single injection of the gonadotropin-releasing hormone analog buserelin on ovulation and endocrine profiles. Twenty-two 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.
authors.affiliation: The United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan; Federation of Hokkaido Agricultural Mutual Aid Associations, Hokkaido 069-0806, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Miki
authors.affiliation: Tokachi Agricultural Mutual Aid Association, Hokkaido 089-1182, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Oniyama
authors.affiliation: Department of Clinical Veterinary Science, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan.
authors.forename: Naomasa
authors.initials: N
authors.lastname: Takeda
authors.affiliation: The United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kimura
authors.affiliation: Department of Clinical Veterinary Science, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Haneda
authors.affiliation: Department of Clinical Veterinary Science, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan.
authors.forename: Motozumi
authors.initials: M
authors.lastname: Matsui
authors.affiliation: Tokyo University of Agriculture and Technology, Tokyo 183-8538, Japan.
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Taya
authors.affiliation: Department of Clinical Veterinary Science, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Nambo
keywords: GnRH analog buserelin; heavy draft mares; ovulation; single injection; uterine edema