Objective—To evaluate gonadotropin secretion and
ovarian function after administration of deslorelin
acetate to induce ovulation in mares.
Design—Randomized controlled trial.
Animals—16 healthy mares with normal estrous
Procedure—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 gonadotropinreleasing
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
Conclusions and Clinical Relevance—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. (J Am Vet Med