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

Abstract

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 AE 2.49%), and the percentage of adult females that was treated on any given year ranged from 42 to 76% (67.78 AE 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.

Fertility control to mitigate human–wildlife conflicts: a review

“…These conclusions have been challenged by models showing that large, Fertility control for human-wildlife conflicts Wildlife Researchlong-lived species might be easier to manage with fertility control than are smaller, shorter-lived ones because a lower proportion of the population would need to be treated (Hone 1999), particularly if lifelong contraceptives were employed (Hobbs et al 2000; Table 2). However, in long-lived species, the benefits of using fertility control to decrease population size are accrued in the long term (Twigg et al 2000;Cowan and Massei 2008;Kirkpatrick and Turner 2008). Others have suggested that contraception is likely to be better than culling for controlling species with medium to high instantaneous rates of population increase, but equivalent to culling for species with low instantaneous rates of population increase (Zhang 2000).…”

Contraceptive Vaccines for Wildlife: A Review

“…A change of adjuvants, to Freund's modified adjuvant (FMA), increased efficacy to 100%. 19,20 Since the completion of these trials, management level application of the PZP vaccine has been successful in altering entire populations, stopping population growth and even decreasing populations, of wild horses, 21 urban deer, 22 wapiti, 23 and African elephants. 19,20 Safety At this point, attention turned to safety issues.…”

“…For wild horses treated with native PZP, efficacy is approximately 95% over 23 years. 21 In the case of white-tailed deer, there is more variability, 11,22 with an efficacy of approximately 75%. Among PZP-treated wapiti, efficacy ranged from a low of 84% to a high of 90%.…”

“…However, for wildlife populations, a variety of modeling 71 and results from field trials 21 have demonstrated that contraceptive vaccines with less than 100% effectiveness will suffice.…”

LACK OF SPATIAL AND BEHAVIORAL RESPONSES TO IMMUNOCONTRACEPTION APPLICATION IN AFRICAN ELEPHANTS (LOXODONTA AFRICANA)

“…Outcomes are most effective when complimentary management induces variable elephant use of landscapes. In addition, adverse behavioral effects as a result of immunocontraception are undesirable from a welfare 4,43,45 as well as an ecologic 40,59 perspective. Early attempts at contraception used hormonal implants.…”