El. Mumford et al., USE OF DESLORELIN SHORT-TERM IMPLANTS TO INDUCE OVULATION IN CYCLING MARES DURING 3 CONSECUTIVE ESTROUS CYCLES, Animal reproduction science, 39(2), 1995, pp. 129-140
Alternatives to human chorionic gonadotropin (hCG) for inducing ovulat
ion in cycling mares over several consecutive cycles were explored. Pl
acebo, one, three or five short-term implants each containing 2.2 mg o
f gonadotropin-releasing hormone (GnRH) analogue (deslorelin) were adm
inistered to cycling mares after identification of a follicle over 30
mm. Mares were treated over three consecutive cycles, and artificially
inseminated during the third cycle only, Serum was assayed for concen
trations of luteinizing hormone (LH), follicle-stimulating hormone (FS
H), and progesterone during each cycle. All deslorelin doses decreased
the interval to ovulation (4.0 days, 2.6 days, 2.4 days and 2.0 days)
, increased the proportion of mares ovulating within 48 h (20.0%, 83.3
%, 73.3% and 85.7%), and decreased the diameter of the largest follicl
e at ovulation (45.8 mm, 38.0 mm, 41.0 mm and 37.2 mm) for the placebo
, 2.2 mg, 6.6 mg and 11.0 mg groups, respectively (P < 0.05). The inte
rovulatory interval was lengthened in the 11.0 mg group compared with
all other groups (21.2 days, 21.8 days, 26.4 days and 32.7 days for th
e placebo, 2.2 mg, 6.6 mg and 11.0 mg groups, respectively, P < 0.05).
No differences (P > 0.05) were detected in serum concentrations of pr
ogesterone or pregnancy rate among the groups. Cycle number had no eff
ect (P > 0.05) on the reproductive parameters or serum concentrations
of progesterone. Concentrations of LH were higher in Cycle 3 in the 6.
6 mg and 11.0 mg groups, and FSH concentrations were decreased in Cycl
es 2 and 3 in treated mares. Deslorelin was efficacious for inducing o
vulation in cycling mares with no diminished activity over three conse
cutive cycles. However, ovarian suppression and changes in serum conce
ntrations of gonadotropins were noted at higher doses.