Hormonal induction of estrus

• Indicated only if prolonged anestrus, resulting in prolonged interestrus interval, is observed.

• Failure to show signs of estrus > 8 months since last observed reproductive cycle.
• Racing or working bitch with testosterone-induced anestrus (several years).
• Show dogs treated with the androgen mibolerone to prevent/postpone estrus.

• Greyhound Greyhound , and several other purebred breeds.
• Working dog.

• Relatively expensive owing to clinical monitoring and hormonal assays to document efficacy of treatment and progression to fertile period for breeding or timed artificial insemination Artificial insemination: non-surgical Artificial insemination: surgical.
• Overall it is a good option for animals of superior breeding value to justify this modality of veterinary intervention.

• Induction of prolonged proestrus and estrus Prolonged pro-estrus and estrus.
• Anovulatory cycles.
• Some evidence for poor conception and pregnancy maintenance rates after induction of estrus.

• Aim to exogenously provide anestrous bitches with a source of gonadotropin-releasing hormone to stimulate ovarian function.
• Prolonged anestrus may occur spontaneously or in androgen-treated bitches.

• Although many protocols to induce estrus in bitches exist detailing the use of steroids, PMSG, FSH, etc, the use of the GnRH analogue deslorelin Deslorelin is currently widely preferred to induce estrus in breeding bitches.

• Deslorelin acetate(2.1 or 4.7 mg) implant → placed subcutaneously just cranial to the umbilical region for ease of removal once ovulation is induced.
• Deslorelin acetate(1.8 mg/ml) injectable solution → 0.5-1.0 ml administered as a single dose IM.
  Deslorelin implants are preferred over the injectable formulations of deslorelin - more variation and failure to induce estrus seen when injectable solutions are used.
  Bitches must be in deep anestrus for best results (serum progesterone <0.5 ng/ml at the time of treatment).

• Serial vaginal exfoliative cytology and serum progesterone measurements starting 3-5 days after treatment with deslorelin:
  • Signs of vulvar hemorrhagic discharge in 4-5 days.
  • Significant vaginal epithelial cornification observed at 5-7 days post-estrus induction.
  • Ovulation typically taking place at 7-12 days post-treatment.

Monitoring

• Once ovulation is confirmed (5-10 ng/ml of serum progesterone), the implant must be removed to prevent potential risks of excessive gonadotropin stimulation leading to down-regulation of GnRH receptors and, consequently, luteal insufficiency.
• Recommended pregnancy examination at 25-30 days post LH surge and assessment of luteal function.

• Good for successful ovulation and pregnancy, and birth of live puppies.

• Ovarian follicle development, normal estrus, ovulation, pregnancy, lactation and puppies.
• Treatment failure is not uncommon:
  • Prolonged proestrus, estrus.
  • Anovulation.
  • Failure to conceive, small litter sizes.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Fontaine E, Mir F, Vannier F, Gerardin A, Albouy M, Navarro C, Fontbonne A (2011) Induction of fertile oestrus in the bitch using Deslorelin, a GnRH agonist. Theriogenology 76, 1561-1566 PubMed.
• Kutzler M A (2007) Estrus induction and synchronization in canids and felids. Theriogenology 68, 354-374 PubMed.