Failure to conceive in deslorelin-induced oestrous bitches with regard to removal of hormone implants after ovulation

Abstract

Removal of a GnRH agonist deslorelin implant either before or during ovulation in deslorelin-induced
oestrous bitches is suggested because prolonged administration of the slow-release agonist may compromise luteal
function secondary to pituitary down-regulation. This study aimed at investigating the effect of 4.7 mg deslorelin
(Suprelorin®) on oestrous induction, ovulation and conception rate after removing the implant 72-96 hours postovulation to ensure that the entire ovulation process was complete. Ovulation began when serum progesterone reached
5-6 ng/mL. The implants were inserted subcutaneously in the umbilical area in 5 healthy, intact anoestrous beagles
(1.5-3 years). Time of implantation was considered as Day 0, and time elapsed from Day 0 to oestrous induction was
calculated. In all bitches, vaginal cytology was abruptly changed on Day 3, and oestrous signs were observed on Day 5
post-implantation. Ovulation occurred in all treated bitches on Days 11.4±0.9 (ranging from 11-13 days) postimplantation. Transcervical artificial inseminations (TCAI) with chilled semen (>75% sperm motility) using
Scandinavian catheter were performed on the 2nd and 4th day post-ovulation. Pregnancy was confirmed on Days 32-35
post-TCAI by transabdominal ultrasonography and serum relaxin test (WITNESS® Relaxin). No foetuses were detected
and the relaxin tests were negative (pregnancy rate = 0%). Of all bitches, progesterone levels were within a normal
range throughout the dioestrus period (62 days). The unsuccessful pregnancy outcome was possibly related to the
delayed removal of the implants. Further study should be conducted to investigate physiological changes in follicular
development, ovulatory process, oocyte quality, oviduct and uterine environment of oestrous-induced bitches in
relation to the time of implant removal.