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  Discussion on Research Summary: GnRH and Preventing Heat (Estrus) in Mares
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DrO

Posted on Thursday, Jul 26, 2007 - 9:54 am:

Here is the best study to date on using immunization techniques for preventing estrus in mares. While the treatment was very successful at preventing physiological estrus is was only 50% effective at preventing behavioral heat. This is not surprising as this treatment causes progesterone to be low and has a important effect on the prevention of behavioral heat. Other down sides was the variability of the length of the effect and one mare had not resumed cycling by 2 years following vaccination.
DrO

Theriogenology. 2006 Nov;66(8):1866-75. Epub 2006 Jun 15.
Influence of immunization against GnRH on reproductive cyclicity and estrous behavior in the mare.

Imboden I, Janett F, Burger D, Crowe MA, Hassig M, Thun R.

National Stud, Avenches, Switzerland.

The aim of this study was to evaluate the effect of active immunization against GnRH on ovarian activity, plasma progesterone and estradiol concentrations and on estrous behavior in adult mares\. Eighteen cyclic mares were randomly divided into a treatment and control group\. Nine mares were immunized twice with 2 mL (400 microg GnRH-protein conjugate) of a GnRH-vaccine (Improvac, CSL Limited, Australia) administered intramuscularly, 4 weeks apart\. Control mares received the same amount of saline solution\. Ovaries and uterus of all mares were examined weekly by ultrasonography from 3 weeks before to 60 weeks after first immunization\. Thereafter, vaccinated mares were evaluated monthly until 100 weeks after first vaccination\. In addition, mares were teased with a stallion for assessment of estrous behavior and blood was collected for progesterone, estradiol-17beta and GnRH antibody titer determination\. Results demonstrate that vaccination against GnRH significantly (P<0.05)>3 cm, progesterone >1 ng/mL) while three mares showed only follicular activity (follicles >3 cm) and one mare remained completely suppressed for the entire duration of the study\. In spite of ovarian suppression, four mares expressed sporadic and one mare continuous estrous behavior\. In conclusion, reproductive cyclicity in adult mares can be successfully suppressed by immunization against GnRH but the timing of resumption of cyclicity is highly variable and estrous behavior may occur in spite of ovarian suppression.

For More Information see the article Suppressing Heat and Estral Behavior in Mares.
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