Efficacy of SpayVac® as a contraceptive in feral horses

Fertility Control for Wildlife: A European Perspective

Trends of human population growth and landscape development in Europe show that wildlife impacts are escalating. Lethal methods, traditionally employed to mitigate these impacts, are often ineffective, environmentally hazardous and face increasing public opposition. Fertility control is advocated as a humane tool to mitigate these impacts. This review describes mammalian and avian wildlife contraceptives' effect on reproduction of individuals and populations, delivery methods, potential costs and feasibility of using fertility control in European contexts. These contexts include small, isolated wildlife populations and situations in which lethal control is either illegal or socially unacceptable, such as urban settings, national parks and areas where rewilding occurs. The review highlights knowledge gaps, such as impact of fertility control on recruitment, social and spatial behaviour and on target and non-target species, provides a decision framework to assist decisions about the potential use of wildlife fertility control, and suggests eight reasons for Europe to invest in this area. Although developing and registering contraceptives in Europe will have substantial costs, these are relatively small when compared to wildlife's economic and environmental impact. Developing safe and effective contraceptives will be essential if European countries want to meet public demand for methods to promote human-wildlife coexistence.

The contraceptive efficacy of a self-assembling intra-uterine device in domestic mares

OBJECTIVE

The primary aim of this study was to investigate the contraceptive efficacy of a self-assembling uterine device (iUPOD™) in the mare. In addition, the effects of iUPODs on oestrous cyclicity, uterine health and circulating concentrations of cortisol were evaluated.

METHODS

Domestic mares underwent oestrous monitoring and artificial insemination. After subsequent ovulation, mares underwent either placement (n = 7) or sham placement (n = 7; controls) of an iUPOD device. Devices were left in place for at least 3 months. Pregnancy diagnoses were carried out 14 days post-ovulation, with any pregnancies terminated at 28 days post-ovulation. All mares underwent weekly blood sampling with or without reproductive examinations throughout the study. Towards the end of the study, multiple serum samples collected over three consecutive days were analysed for concentrations of cortisol. Endometrial biopsies were collected before artificial insemination and during the subsequent breeding season. Endometrial cytology and bacterial cultures were performed before device removal (iUPOD mares) or at the end of the study (control mares).

RESULTS

Pregnancies were diagnosed in 0 of 7 iUPOD mares versus 7 of 7 control mares. Placement of iUPODs was associated with extended luteal phases and variable accumulations of intra-uterine fluid. Bacterial culture results suggested that the mild endometritis associated with iUPODs was sterile in six of seven mares. Short-term placement of iUPODs had no detrimental effects on endometrial architecture. Mean serum cortisol concentrations were significantly lower in iUPOD mares than control mares.

CONCLUSION

iUPODs represent a promising means of fertility control in the mare.

Efficacy and safety of native and recombinant zona pellucida immunocontraceptive vaccines in donkeys

Feral and semi-feral donkeys are recognised as a problem in some world regions. The main problem associated with uncontrolled donkey populations is habitat degradation and competition for feed resources, especially in arid climes. Controlling population numbers would reduce the impact of donkeys and other species. While removal by various means is effective, it has been shown to stimulate reproductive rate. Probably the most effective and humane solution is reducing reproduction using minimally invasive methods including immunocontraception. This study tested the immunocontraceptive efficacy and safety of zona pellucida (ZP) vaccines, both recombinant (reZP; three treatments) and native porcine (pZP; two treatments) vaccines formulated with Freund's modified complete (primary) and Freund's incomplete (boosters) adjuvants in donkey jennies. Control jennies received adjuvants only (two treatments). Twenty-five non-pregnant jennies were randomly assigned to reZP (n = 9), pZP (n = 8) or control (n = 8) groups. Weekly monitoring of the reproductive tract and ovaries via transrectal palpation and ultrasound and inspection of injection sites was conducted and anti-pZP antibody titers were measured. Five weeks after last treatment, one donkey jack was introduced to each group and rotated every 21 days. By 232 days after last treatment the number pregnant and median days to pregnancy was 2/9 and 214 (reZP group), 1/8 and 196 (pZP group) and 8/8 and 77 (control group). Median time to ovarian shut-down was 77 (9/9) and 56 (7/8) days for reZP and pZP groups, respectively. This was observed in association with a distinct reduction in mean uterine diameter. The antibody response was equally good for both ZP-treated groups. Incorporation of Freund's adjuvants initially produced a high incidence of side effects from local swelling and intermittent lameness followed weeks later by sterile abscesses (reZP, 9/9; pZP, 7/8; control, 3/8). Both ZP vaccines effectively controlled reproduction in jennies, albeit with a high incidence of adjuvant-associated side effects.

Efficacy of dart-delivered PZP-22 immunocontraceptive vaccine in wild horses (Equus caballus) in baited traps in New Mexico, USA

Abstract Context Federally protected wild horses on public lands are undergoing population growth that overwhelms the historical management strategy of removal and adoption. Porcine zona pellucida (PZP) has been used as an injectable immunocontraceptive vaccine to induce reversible infertility in free-roaming horses. PZP vaccination during February and March, which is the optimal time for administering current vaccines, is not possible for the herd on Jarita Mesa Wild Horse Territory (JM WHT), New Mexico, due to severe weather, terrain and subject wariness. AimsThe first goal was to assess bait trapping and remote darting as a minimally disruptive alternative to helicopter gathers for treatment. The second goal was to quantify the efficacy over 2 years following spring treatment with a single injection of PZP-22 (a combination of PZP-adjuvant emulsion and controlled-release pellets) by remote dart delivery. Methods Bait trapping and dart delivery of PZP-22 was carried out on JM WHT from 4 April to 16 June 2012. The herd was observed in the summers of 2011, 2013 and 2014 to determine the foaling status of the study mares. Outcome (foal or no foal) as a function of treatment was analysed using Fisher’s exact test. Key resultsThere were 157 individuals, including 66 females >1 year old, documented in 2011. In 2012, 26 females (including three yearlings) identified by colour and markings were bait trapped and darted with PZP-22. The proportion of treated females foaling was lower than that of untreated females in 2013 and 2014, but the difference was only significant in 2013. Of the treated mares observed in 2013, the two that foaled were the last two treated in 2012. Untreated mares >4 years old were significantly more likely to foal than younger mares. Conclusions Bait trapping at JM WHT permitted successful delivery of PZP-22 in a previously inaccessible herd. Dart administration of PZP-22 in April–June induced at least 1 year of measurable infertility. Implications This is the first demonstration of the efficacy of an initial treatment of PZP-22 delivered by dart instead of hand injection. Considerations for PZP-22 treatment include seasonal timing of treatments and age of treated mares. Treatments need to take place early enough to allow antibody titers to build to contraceptive levels before the breeding season.

IgG4/7 responses correlate with contraception in mares vaccinated with SpayVac

SpayVac^® is an immunocontraceptive vaccine based on porcine zona pellucida (pZP) antigens and uses a patented liposome formulation (VacciMax^™ or DepoVax^®). It has delivered single-dose, long-lasting (4-10 years) immunocontraception in several species. Previous studies have demonstrated a positive correlation between levels of pZP antibodies produced and contraceptive effect; however, individual mares that were consistently infertile did not necessarily have the highest antibody titers. The objective of this study was to identify potential differences in specific immunoglobulin G (IgG) isotype responses among mares treated with SpayVac (VacciMax formulation) to improve our understanding of vaccine efficacy and potential management applications. We analyzed serum samples collected 1, 2 and 4 years post-vaccination from mares in another study that were continuously infertile or had foaled at least once during the 4-year period (n = 14 each). Additional samples from the continuously infertile mares were collected 5 years post-vaccination. A fluorescent bead-based assay was used to distinguish IgG isotype responses against pZP. IgG1 antibodies were generally higher in the infertile compared to the fertile mares, but only IgG4/7 antibodies were significantly higher in infertile mares during years 1 and 2 post-vaccination (p < 0.05). Interestingly, IgG4/7 isotype levels were significantly higher during year 5 compared to year 4 in the continuously infertile mares (p < 0.02). SpayVac's ability to preferentially stimulate IgG4/7 antibodies may contribute to its long-term immunocontraceptive efficacy, and measuring IgG4/7 isotypes may help differentiate effectively contracepted mares from those that may need additional vaccination.

Could current fertility control methods be effective for landscape-scale management of populations of wild horses (Equus caballus) in Australia?

Context Fertility control is seen as an attractive alternative to lethal methods for control of population size and genetic diversity in managed animal populations. Immunocontraceptive vaccines have emerged as the most promising agents for inducing long-term infertility in individual animals. However, after over 20 years of scientific testing of immunocontraceptive vaccines in the horse, the scientific consensus is that their application as a sole management approach for reducing population size is not an effective strategy. Aims The purpose of this review is to evaluate currently available non-lethal fertility-control methods that have been tested for their contraceptive efficacy in Equidae, and to assess their suitability for effective management of wild (feral) horses in an Australian setting. Key results (1) Fertility-control agents, particularly injectable immunocontraceptive vaccines based on porcine zona pellucida (PZP) or gonadotrophin-releasing hormone (GnRH), can induce multi-year infertility (up to 3 years) in the horse. Some formulations require annual or biennial booster treatments. Remote dart delivery (on foot) to horses is possible, although the efficacy of this approach when applied to large numbers of animals is yet to be determined. (2) The proportion of females that must be treated with a fertility-control agent, as well as the frequency of treatment required to achieve defined management outcomes (i.e. halting population growth in the short term and reducing population size in the long term) is likely to be >50% per annum. In national parks, treatment of a large number of wild horses over such a broad area would be challenging and impractical. (3) Fertility control for wild horses could be beneficial, but only if employed in conjunction with other broad-scale population-control practices to achieve population reduction and to minimise environmental impacts. Conclusions In Australia, most populations of wild horses are large, dispersed over varied and difficult-to-access terrain, are timid to approach and open to immigration and introductions. These factors make accessing and effectively managing animals logistically difficult. If application of fertility control could be achieved in more than 50% of the females, it could be used to slow the rate of increase in a population to zero (2–5 years), but it will take more than 10–20 years before population size will begin to decline without further intervention. Thus, use of fertility control as the sole technique for halting population growth is not feasible in Australia.