Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats

Achieving population goals in a long-lived wildlife species (Equus caballus) with contraception

Jay F. Kirkpatrick A C and Allison Turner B

A The Science and Conservation Center, 2100 South Shiloh Road, Billings, MT 59106, USA.

B Assateague Island National Seashore, Berlin, MD 21811, USA.

C Corresponding author. Email: zoolab@wtp.net

Wildlife Research 35(6) 513-519 http://dx.doi.org/10.1071/WR07106
Submitted: 28 July 2007  Accepted: 2 May 2008   Published: 22 October 2008


The ultimate goal of any wildlife contraceptive effort is some alteration of the target population, either through a slowing of growth, or stabilisation or reduction of the population. Early population models suggested that short-term contraceptive agents applied to long-lived species would not achieve significant population changes. Native porcine zona pellucida antigen (PZP), a short-term contraceptive vaccine, was applied to a herd of wild horses inhabiting Assateague Island National Seashore, MD, USA, over a 13-year period, with an immediate goal of achieving zero population growth, a secondary goal of reducing the population from 175 to 150 and a tertiary goal of reaching 120 individuals, all without the physical removal of animals. Contraceptive efficacy ranged from 92 to 100% on an annual basis (96.28 ± 2.49%), and the percentage of adult females that was treated on any given year ranged from 42 to 76% (67.78 ± 18.21%). The goal of zero population growth was achieved in 2 years, an initial decline in the population became apparent in 8 years and by Year 11, the population declined to 135, a decrease of 22.8%. The lengthy period required for achieving a population decline was caused by increasing body condition scores, reduced mortality and significantly increased longevity among treated females.

Additional keywords: equids, fertility control, horses, immunocontraception, population, zona pellucida.


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