Effect of deslorelin acetate on gonadotropin secretion and ovarian follicle development in cycling mares.
OBJECTIVE
To evaluate gonadotropin secretion and ovarian function after administration of deslorelin acetate to induce ovulation in mares.


METHODS
Randomized controlled trial.


METHODS
16 healthy mares with normal estrous cycles.


METHODS
8 control mares were allowed to ovulate spontaneously, whereas 8 study mares received deslorelin to induce ovulation when an ovarian follicle > 35 mm in diameter was detected. Follicle development and serum concentrations of gonadotropins were monitored daily during 1 estrous cycle. Pituitary responsiveness to administration of gonadotropin-releasing hormone (GnRH) was evaluated 10 days after initial ovulation.


RESULTS
Interovulatory intervals of mares treated with deslorelin (mean +/- SD, 25.6 +/- 2.6 days) were longer than those of control mares (22.9 +/- 1.8 days). Diameter of the largest follicle was significantly smaller during 2 days of the diestrous period after ovulation in deslorelin-treated mares than in control mares. Concentrations of follicle-stimulating hormone (FSH) were lower in deslorelin-treated mares on days 5 through 14 than in control mares. Concentrations of luteinizing hormone were not different between groups during most of the cycle. Gonadotropin release in response to administration of GnRH was lower in mares treated with deslorelin acetate than in control mares.


CONCLUSIONS
Administration of deslorelin was associated with reduction in circulating concentrations of FSH and gonadotropin response to administration of GnRH during the estrous cycle. Low concentration of FSH in treated mares may lead to delayed follicular development and an increased interovulatory interval.
Equine Reproduction Laboratory, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins 80523, USA.
V J
VJ
Farquhar
P M
PM
McCue
T M
TM
Nett
E L
EL
Squires
D000818:Animals; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists* / Q000031:analogs & derivatives / Q000494:pharmacology*; D006062:Gonadotropins / Q000378:metabolism*; D006736:Horses / Q000502:physiology*; D006080:Ovarian Follicle / Q000187:drug effects / Q000502:physiology*; D010062:Ovulation Induction / Q000662:veterinary; D013997:Time Factors; D017329:Triptorelin Pamoate / Q000031:analogs & derivatives
D006062:Gonadotropins; D017329:Triptorelin Pamoate; D007987:Gonadotropin-Releasing Hormone; D005640:Follicle Stimulating Hormone; C066438:deslorelin