Immunocontraception in Wild Horses: One Inoculation Provides Two Years of Infertility

Authors

  • JOHN W. TURNER JR.,

    Corresponding author
    1. Department of Physiology & Pharmacology, University of Toledo College of Medicine, 3035 Arlington Avenue, Toledo, OH 43614, USA
      E-mail: jturner@meduohio.edu
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  • IRWIN K. M. LIU,

    1. Department of Population, Health & Reproduction, School of Veterinary Medicine, 1114 Tupper Hall, Medical Science Building 1-A, University Of California, Davis, Davis, CA 95616, USA
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  • DOUGLAS R. FLANAGAN,

    1. Department of Pharmacy, University of Iowa, College of Pharmacy, 115 S. Grand Avenue, Iowa City, IA 52242, USA
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  • ALLEN T. RUTBERG,

    1. Center for Animals & Public Policy, Tufts University School of Veterinary Medicine, 200 Westboro Road, North Grafton, MA01536, USA
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  • JAY F. KIRKPATRICK

    1. Science & Conservation Center, 2100 S. Shiloh Road, Billings, MT 59106, USA
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E-mail: jturner@meduohio.edu

Abstract

ABSTRACT ABSTRACT Previous studies reported one year of contraception associated with a 1-injection porcine zona pellucida (PZP) vaccine. We have subsequently determined contraceptive effectiveness of a presumptive 1-injection, 2-year-duration PZP vaccine in free-roaming wild horses (Equus caballus) in Nevada, USA. In January 2000, we captured, freeze-branded, treated, and subsequently released 96 adult females that received 1) a primary dose of vaccine emulsion consisting of aqueous PZP and Freund's Complete Adjuvant, and 2) booster doses of PZP and adjuvant in controlled-release polymer pellets. We determined PZP release characteristics of pellets in vitro, prior to field use. We determined reproductive success in treated and untreated females through October 2004 via measurement of estrone sulfate and progesterone metabolites in fresh feces collected from the ground and by twice-annual foal counts. Among treated females, annual reproductive success from 2001 though 2004 sequentially was 5.9%, 14.0%, 32.0%, and 47.5%. Untreated females showed average reproductive success of 53.8 ± 1.3% across this period. This study revealed that: 1) PZP acted as an effective contraceptive for 2 years posttreatment; 2) some residual contraceptive effect remained in year 3; and 3) fertility returned to control levels by year 4 posttreatment. It appears that controlled-release technology can replace both the second(1-month) and annual booster injection of PZP vaccine, thereby decreasing cost and increasing efficiency of use of this vaccine in wild horse management.

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