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Pulsatile administration of GnRH to induce estrus and Ovulation in the bitch

Shawna Walters and D.C. Kraemer, D.V.M., Ph.D.

Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Texas A&M University

Introduction and Background

The Missyplicity Project encompasses many aspects of reproductive technology including:  oocyte collection and maturation, production of clones through nuclear transfer, embryo culture and transfer, and estrous cycle manipulation of donors and recipients.  The reproductive cycle of the bitch is much different than most other domestic species.  The average bitch has long inter-estrous intervals as well as lengthy diestrous and anestrous cycle stages, which make reproductive studies more challenging.  Shortening of the normal canine cycle would be a great benefit as it would increase the opportunities for reproductive activities.  According to sources that have worked with compounds used to manipulate cycles in bitches, some products have been more effective than others.  Administration of GnRH seems to be dose dependent and appears more effective at doses above 280 ng/kg.   Endogeneous GnRH release that stimulates the release of FSH has been reported to occur in pulses about 90 minutes apart for 9 days +/-3 days.  This project involves stimulation of estrus and ovulation in aestrous bitches, by mimicking endogeneous GnRH release with pulsatile administration of GnRH via an IV infusion pump.  By better simulating the body's own mechanisms, we are hoping for more successful ovulations and less complications than are associated with other exogeneous hormones (ie cystic ovaries).  When an effective protocol is eventually identified it can be used in the cloning project to synchronize bitches for embryo transfer, and for oocyte harvesting.