Long-Term Efficacy of Three Contraceptive Approaches for Population Control of Wild Horses

Abstract

Controlling fertility of feral horses through the use of long-acting contraceptives or sterilization approaches has been championed as a reasonable and humane solution for addressing overpopulation problems in several western states. However, methods to accomplish long-term contraceptive efficacy of horses following a single treatment have been lacking. In fall 2002 and spring 2003, we initiated a study to compare the long-term efficacy of a single-shot contraceptive vaccine directed at gonadotropin releasing hormone (GonaCon ™) to that of a single-shot vaccine directed at the zona pellucida (SpayVac) and to the use of intrauterine contraceptive devices (IUD). Both vaccines were administered with AdjuVac ™ , an adjuvant developed at the National Wildlife Research Center. The objectives of the study were to determine: 1) 3-year efficacy for preventing pregnancy, 2) whether the contraceptive effects are reversible, and 3) whether there are contraindications. The Nevada Department of Agriculture provided the feral mares, which were maintained at the Nevada State Penitentiary, Carson City, facility. Mares were dewormed and given health vaccinations annually. Eight untreated control mares were compared to 12 mares treated with SpayVac, 16 mares treated with GonaCon ™ , and 15 mares treated with copper-containing IUDs. Only 25% (2/8) of the control mares were not pregnant or infertile in the first year. All mares in the SpayVac group were infertile, and 94% (15/16) were infertile in the GonaCon ™ group during the first breeding season. In Year 2, 80% (10/12) of the SpayVac-treated mares and 60% (9/15) of the GonaCon ™-treated mares were infertile. In Year 3, 80% of the SpayVac mares and 53% (8/15) of the GonaCon ™-treated mares were infertile. For IUD-treated mares, 80% (12/15) were infertile after Year 1, but only 29% (4/14) and 14% (2/14) were infertile after Years 2 and 3, respectively. For IUD mares that were infertile, it was possible to visualize the IUD by ultrasonography, leading us to conclude that mares that became pregnant had lost their IUDs. For mares given SpayVac, uterine edema was commonly observed. In Years 2 and 3, antibody titers for SpayVac were progressively lower compared to titers observed in Year 1.

Effects of two porcine zona pellucida immunocontraceptive vaccines on ovarian activity in horses

“…Local injection site reactions are not uncommon, and a variety of factors have been proposed as contributors to their formation, including concurrent vaccinations that may result in cross‐reacting epitopes (Miller et al ), water‐in‐oil emulsions (Gupta et al ), and oils comprised of shorter chain carbon lengths (Fukanoki et al ). Miller et al () suggested that epitopes on the surface of killed Streptococcus equi in strangles vaccines were cross‐reacting with epitopes on M. avium , contributing to the injection site reactions seen in mares simultaneously vaccinated with GonaCon (Killian et al ). However, in our study, mares were given only viral preventive health vaccines prior to administration of SpayVac, so injection site reactions were unlikely potentiated by this mechanism.…”

Ecological and human dimensions of management of feral horses in Australia: a review

“…Empirical evidence gathered from research on the acceptance of control methods for large herbivores supports this (see Stout et al 1997;Lauber et al 2001). However, although research on fertility control of feral horses has been underway for over 25 years (Turner et al 2001), and despite promising results from recent trials (see Kirkpatrick et al 1997;Turner et al 2001;Killian et al 2004), there still exists no proven costeffective method for long-term fertility control of feral horses at a population level (English 2000;Killian et al 2004;Hinds 2006).…”

Four-year contraception rates of mares treated with single-injection porcine zona pellucida and GnRH vaccines and intrauterine devices

“…However, wild horses vaccinated with PZP preparations have required revaccination every year or two to maintain infertility (Turner et al 2001. Limited data exist for the use of GnRH vaccines in mares to control fertility, ovarian function or behaviour (Dalin et al 2002;Killian et al 2004Killian et al , 2006bImboden et al 2006;Elhay et al 2007). Information on multiyear efficacy and effects following a single injection of a GnRH vaccine in mares is lacking.…”

“…In addition, on the basis of preliminary studies with pony mares, we evaluated the use of an intrauterine contraceptive device (IUD), the 380 copper 'T', which has been shown to be safe and efficacious in humans for multiple years (Fortney et al 1999;Wu et al 2000). Preliminary results of these studies with Nevada mustangs have been reported earlier (Killian et al , 2006b. This paper reports results for these contraceptive approaches after four years of study with Nevada mustangs and five years of observation on the use of IUDs in pony mares.…”