Effects of Two, Single-Dose pZP Vaccine Formulations on Ovarian Activity in Mares (Equus caballus)
American Association of Zoo Veterinarians Conference 2011
Ursula Bechert1, DVM, PhD; Jennifer Bartell2; Michelle Kutzler2, DVM, PhD, DACT; Fred Menino2, PhD; Robert Bildfell3, DVM, PhD, DACVP; Makensie Anderson3; Mark Fraker4, MA
1College of Science, Oregon State University, Corvallis, OR, USA; 2Department of Animal Sciences, Oregon State University, Corvallis, OR, USA; 3College of Veterinary Medicine, Oregon State University, Corvallis, OR, USA; 4TerraMar Environmental Research Ltd, Sidney, BC, Canada


Humane alternatives to adoption and long-term holding are needed to effectively manage wild horse populations, which can have growth rates as high as 22%. Porcine zona pellucida (pZP) immunocontraception currently has the greatest potential to control fertility because it is easy to administer and safe. ImmunoVaccine Technologies, Inc. (IVT) in Halifax, Canada produces the only pZP vaccine with proven single-dose multi-year contraceptive efficacy (SpayVac®), which makes it practical and economical for broad-scale field application. The effect on ovarian activity of two single-injection formulations, SpayVac®/Modified Freund’s Adjuvant (MFA) non-aqueous or SpayVac®/MFA aqueous, compared to controls (n=7 per group) were assessed in a 7-mo study.

Comparative reproductive parameters included serum concentrations of progesterone (P4) determined by ELISA, ovarian activity assessed by transrectal ultrasound and palpation, as well as gross and histologic examination of ovaries upon necropsy (n=9 or 3 from each group) or after ovariectomy (n=12 or 4 from each group). Mean (P4) were significantly lower in the non-aqueous MFA treatment group compared to control mares (p<0.05), and ovarian weights were lower in this group as well (p<0.00001). The non-aqueous and aqueous MFA treatment groups had significantly smaller-sized ovaries and fewer follicles (p<0.05) compared to the control. Most mares vaccinated with the non-aqueous MFA (6/7) and the aqueous MFA (3/7) SpayVac® formulations ceased cycling 1–2 mo prior to the end of the study; whereas all control mares continued to cycle throughout the study. Research with 90 free-ranging mares to test contraceptive efficacy of the SpayVac®/MFA non-aqueous and aqueous formulations is underway.


The authors thank Scot Greenwood and his staff for their assistance in the care of these mares. Makensie Anderson, Amanda Kyser, and Scott Oeffner collected weekly blood samples, and Scott helped with routine transrectal ultrasounds as well. The authors also thank Dr. Leon Pielstick, who performed the ovariectomies. This project was funded by a grant from USGS (G10AP00087).


Speaker Information
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Ursula Bechert, DVM, PhD
College of Science
Oregon State University
Corvallis, OR, USA

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