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

Characteristics of potential adopters of wild horses and their willingness-to-pay for wild horses

An overabundance of wild horses and burros on federal lands can lead to suboptimal welfare when there are insufficient forage and water resources. Placing some of these animals in private homes has been identified as a key part of the solution. A nationwide online survey completed by 2,247 current and former horse owners is used to assess the feasibility of accommodating this strategy. The survey tool addressed basic horse ownership and demographic information, previous experience with wild horses, and hypothetical wild horse adoption scenarios. Results suggest that most respondents are receptive to the idea of adopting a wild horse, with previous adopters and younger potential adopters showing greater willingness-to-pay. By reducing existing barriers to adoption, which includes educating the horse-owning public on adoption requirements, expanding the training of wild horses, and targeting certain age groups of potential adopters, our study suggests that it may be possible to increase the annual number of adoptions over current levels. With appropriate and informed strategies, enhanced welfare of privately adopted and on-range animals can be achieved.

Immunocontraceptive Efficacy of Native Porcine Zona Pellucida (pZP) Treatment of Nevada's Virginia Range Free-Roaming Horse Population

In North America, range constraints due to burgeoning development increasingly encroach on wild horse habitat and necessitate effective but humane reproductive management. The largest free-roaming wild horse fertility control program by population (>3500) and territory size (≈300,000 acres) is located within Nevada's Virginia Range. Data from a field study investigated porcine zona pellucida (pZP) immunocontraception via remote dart delivery to mares in this population. Analyses aimed to measure efficacy by treatment effects on annual birth rates and population demographics and to evaluate treatment frequency and season against these variables. Analyses included mares' monthly data (January 2019-December 2022; 48 months), characterized by cumulative vaccination numbers subset into four classifications considering the vaccine as having no loss of efficacy or a loss within a 6-, 12-, and 18-month period post vaccination; from foaling data, the likelihood of being in foal and of conceiving in that month; and from age, as mature or immature (<1 years-old). A downward foaling rate and trend in the numbers of mature mares, descriptively presented at monthly intervals, showed markedly declining annual seasonal breeding peaks, with no observed change in foaling season or duration. Within four years, population coverage surpassed 70% and was associated with a 58% reduction in foaling, with only a 10% conception rate. Vaccinated mares increased proportionally: assuming a 12-month decay rate, the system reached stability at an average ≈1.0 vaccination/mare/year, providing a robust recommendation for treatment frequency contributing to best management practices.

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.

Plant-Produced Mouse-Specific Zona Pellucida 3 Peptide Induces Immune Responses in Mice

Contraceptive vaccines are designed to stimulate autoimmune responses to molecules involved in the reproductive process. A mouse-specific peptide from zona pellucida 3 (mZP3) has been proposed as a target epitope. Here, we employed a plant expression system for the production of glycosylated mZP3 and evaluated the immunogenicity of plant-produced mZP3-based antigens in a female BALB/c mouse model. In the mZP3-1 antigen, mZP3 fused with a T-cell epitope of tetanus toxoid, a histidine tag, and a SEKDEL sequence. A fusion antigen (GFP-mZP3-1) and a polypeptide antigen containing three repeats of mZP3 (mZP3-3) were also examined. Glycosylation of mZP3 should be achieved by targeting proteins to the endoplasmic reticulum. Agrobacterium-mediated transient expression of antigens resulted in successful production of mZP3 in Nicotiana benthamiana. Compared with mZP3-1, GFP-mZP3-1 and mZP3-3 increased the production of the mZP3 peptide by more than 20 and 25 times, respectively. The glycosylation of the proteins was indicated by their size and their binding to a carbohydrate-binding protein. Both plant-produced GFP-mZP3-1 and mZP3-3 antigens were immunogenic in mice; however, mZP3-3 generated significantly higher levels of serum antibodies against mZP3. Induced antibodies recognized native zona pellucida of wild mouse, and specific binding of antibodies to the oocytes was observed in immunohistochemical studies. Therefore, these preliminary results indicated that the plants can be an efficient system for the production of immunogenic mZP3 peptide, which may affect the fertility of wild mice.

Efficacy and Safety of Native and Recombinant Zona Pellucida Immunocontraceptive Vaccines Formulated with Non-Freund's Adjuvants in Donkeys

This study aimed to test zona pellucida (ZP) vaccines’ immunocontraceptive efficacy and safety when formulated with non-Freund’s adjuvant (6% Pet Gel A and 500 Μg Poly(I:C)). Twenty-four jennies were randomly assigned to three treatment groups: reZP (n = 7) received three doses of recombinant ZP vaccine; pZP (n = 9) received two doses of native porcine ZP; and Control group (n = 8) received two injections of placebo. Jennies were monitored weekly via transrectal ultrasonography and blood sampling for serum progesterone profiles and anti-pZP antibody titres. In addition, adverse effects were inspected after vaccination. Thirty-five days after the last treatment, jacks were introduced to each group and rotated every 28 days. Vaccination with both pZP and reZP was associated with ovarian shutdown in 44% (4/9) and 71% (4/7) of jennies, 118 ± 33 and 91 ± 20 days after vaccination, respectively (p > 0.05). Vaccination delayed the chances of a jenny becoming pregnant (p = 0.0005; Control, 78 ± 31 days; pZP, 218 ± 69 days; reZP, 244 ± 104 days). Anti-pZP antibody titres were elevated in all vaccinated jennies compared to Control jennies (p < 0.05). In addition, only mild local injection site reactions were observed in the jennies after treatment. In conclusion, ZP vaccines formulated with non-Freund’s adjuvant effectively controlled reproduction in jennies with only minor localised side effects.

Of Elephants and Other Mammals: A Comparative Review of Reproductive Tumors and Potential Impact on Conservation

Reproductive tumors can impact conception, pregnancy, and birth in mammals. These impacts are well documented in humans, while data in other mammals are limited. An urgent need exists to understand the reproductive impact of these lesions in endangered species, because some endangered species have a documented high prevalence of reproductive tumors. This article documents that the prevalence of both benign and malignant neoplasia differs between African and Asian elephants, with Asian elephants more frequently diagnosed and negatively affected by both. The prevalence of these tumors across mammalian species is compared, and impact plus treatment options in human medicine are reviewed to inform decision making in elephants. Evidence suggests that reproductive tumors can negatively impact elephant conservation. Future studies that document reproductive outcomes, including the success of various treatment approaches in elephants with tumors will benefit conservation efforts.

Evaluation of Stress Accompanying Immunocontraceptive Vaccination in Donkeys

Simple Summary

The overpopulation of donkeys is of concern worldwide. Some of the concerns associated with uncontrolled donkey populations are the destruction of habitat, competition for feed resources, and negative human–animal interactions. One of the most effective and humane solutions is the use of immunocontraception. Immunocontraception is the use of an animal’s immune system to prevent it from fertilizing offspring by the administration of a vaccine that targets a specific portion of the reproductive system. This study sought to measure and compare the amount of stress that is imposed when two different immunocontraceptives were administered to female donkeys. The results showed that physical exam parameters (temperature, pulse, and respiration) were not affected significantly but the measurement of stress hormones suggests an acute stress response after the first vaccination that was followed by a chronic stress response after a booster vaccination 35 days later, especially in donkeys that had reactions at the injection site. Further studies would be required to identify and reduce the stress associated with the immunocontraception vaccines that were used.

Abstract

The overpopulation of donkeys is recognized as a problem in many parts of the world. The main concerns with uncontrolled donkey populations are habitat degradation and competition for feed resources between donkeys and other species. One of the most effective and humane solutions is the use of immunocontraception. Therefore, this study sought to evaluate the stress imposed by the use of two formulations of a zona pellucida (ZP) vaccine, a recombinant (reZP) and a native porcine (pZP) vaccine, both formulated with a Freund’s adjuvant. The stress was objectively measured using fecal cortisol concentrations and physical examination parameters at fixed points before and after vaccination. We hypothesized that fewer changes in physical exam parameters and lower fecal cortisol concentrations would be stimulated in jennies treated with the reZP vaccine due to the selection of specific proteins. Twenty-five reproductively sound jennies were randomly assigned to reZP (n = 9), pZP (n = 8) or control (n = 8) groups. The vaccines were administered at five-week intervals. Physical exam parameters and body wall thickness of injection sites were recorded for each jenny for four days post-injections. Fecal samples were obtained every other day from day 0 (first vaccination) through day 6 and on days 35 to 41 after booster. Injection site reactions were common in all groups with the reZP and pZP groups being overrepresented. Lameness was observed in the pZP and reZP groups that were affected by injection site reactions and open abscesses. The present study showed an increase in fecal cortisol concentrations within 4 days after the first vaccination with ZP vaccines and, thereafter, a decrease in cortisol 35 days later after the second vaccination, especially in donkeys with open abscesses. Our results suggest that acute stress (increased cortisol) was induced after the first vaccination, and chronic stress (decreased cortisol) occurred thereafter in association with open abscesses. In conclusion, reZP and pZP formulated with Freund’s adjuvant induced local inflammatory reactions with a differential degree of acute and chronic stress in donkeys.

Anti-Müllerian hormone in managed African and Asian rhino species

Serum collected across the lifespan of four managed rhino species: black (Diceros bicornis, n = 16), white (Ceratotherium simum simum, n = 19), greater one-horned (GOH, Rhinoceros unicornis, n = 11) and Sumatran (Dicerorhinus sumatrensis, n = 6) were validated and analyzed in an anti-Müllerian hormone (AMH) enzyme- linked immunoassay. Concentrations of AMH were examined over time, between sexes and throughout different reproductive states which included n = 3 female white rhinos immunocontracepted with porcine zona pellucida (pZP). Across species, males produced higher AMH concentrations compared to females. Among males, AMH concentrations varied by species aside from comparable values secreted between black and white rhinos. The GOH and Sumatran rhino secreted the highest and lowest male AMH concentrations, respectively. However, within each species, AMH concentrations were similar across male age categories. Preliminary insight into male AMH changes from birth to sexual maturity suggest its potential as a marker for onset of testicular maturation. Female black, GOH and Sumatran rhinos secreted comparable AMH concentrations which were higher than those in white rhino. Within each species, inter-individual variation in AMH secretion occurred among females of similar age. While AMH secretion did not differ across the ages sampled for female white (4->26 yr) and GOH (4-26 yr) rhinos, black and Sumatran rhinos >26 and <4 yr, respectively secreted lower AMH compared to conspecific females 7-26 yr of age. Two idiopathic infertility cases corresponded to low (outside species range) AMH values. The establishment of normative AMH concentrations in managed African and Asian rhinos provides an additional metric beyond traditional sex steroids to assess gonadal function. Further work is needed to determine if AMH can predict fertility potential in rhinos.

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.

Home off the Range: The Role of Wild Horse Internet Adoptions in Informing Sustainable Western United State Rangeland Management

According to the Bureau of Land Management (BLM), there are about 60,000 more wild horses and burros roaming the rangelands in the western United States than the land can sustain. While the BLM is pursuing a number of strategies to address this imbalance, placing wild horses and burros in private homes is one of the most preferred options. However, little is known about the demand for wild horses. This paper utilizes data from internet adoptions of wild horses to better understand the demand side of the market. More specifically, results from a Heckman selection model provide estimates of the market value of various characteristics of wild horses. By describing adopter preferences, these estimates can aid policy makers in optimizing strategies to manage the wild horse population.

Researching immunocontraceptive vaccines with mares (Equus caballus) as both a target and model for African elephant (Loxodonta africana) cows: A review

A sequence of studies is reviewed that reported the domestic horse (Equus caballus) mare as an appropriate and accessible research platform for recording clinical and laboratory data post-immunisation with anti- GnRH and -zona pellucida (ZP) immunocontraceptive vaccines. Experience with a native porcine ZP (pZP) vaccine in African elephant (Loxodonta africana) cows highlighted needs for improving vaccine formulations and more clearly defining associated ovarian effects and safety profiles. Initially, the efficacy, reversibility and safety of the GnRH vaccine Improvac^® in mares was demonstrated using reproductive tract ultrasonography and concurrently measuring serum antibody titres and progesterone concentrations. Results informed the study design and minimally invasive monitoring of post-treatment ovarian steroid responses of this vaccine in free-ranging African elephant cows. A subsequent sequence of studies reported reversible contraceptive and immunological efficacy in pony mares immunised with pZP formulated with Freund's adjuvants. By comparison, mares treated with a recombinant ZP3 and ZP4 (reZP) vaccine showed disappointing responses. Unexpectedly, most pZP-treated mares showed ovarian inactivity. In attempting to understand this response, results showed the involvement of cytotoxic (CD8+) T-cells negatively correlated to serum ovarian steroid and anti-Müllerian hormone (AMH) levels. Of concern was the prevalence of injection-site lesions ascribable to Freund's adjuvants. Following this, mares treated with both pZP and a novel reZP vaccine formulated with non-Freund's adjuvants showed comparable immunological responses and ovarian inactivity, notably without adverse treatment reactions. In addition, measuring AMH showed promise for monitoring ovarian function in anti-ZP-treated animals.

The application of naked DNA plasmid (DrZP3) and recombinant adenovirus (Ad-rZP3) in rat animal model to determine comparative efficacy of ZP3-Immunocontraceptive vaccines

The common physical and chemical methods for controlling rat pest are less than satisfactory and inhumane. Immunocontraception approach has been considered more humane and it can be accomplished by inducing the relevant host immune response that block further development of reproductive gametes. ZP3 proteins are known to play very important role during sperm-ovum fertilization. It is a self-antigen and only localized in female ovaries. Therefore, an immunization with ZP3 protein elsewhere will induce a generalize host immune response against ZP3 protein. This study employed rat ZP3 (rZP3) gene prepared from its cDNA of Rattus rattus diardii. It was delivered and expressed in vivo by naked plamid DNA (DrZP3) or recombinant ZP3-Adenovirus (Ad-rZP3). Expression studies in vitro with DrZP3 or Ad-ZP3 showed rZP3 proteins were successfully expressed in Vero cells. Hyperimmune serum against rZP3 that were prepared by immunizing several rats with purified rZP3-pichia yeast fusion protein showed it blocked sperms from binding DrZP3-transfected Vero cells. Female Sprague Dawley rats immunized with DrZP3 demonstrated a long-term effect for significant reduction of fertility up to 92.6%. Ovaries from rats immunized with DrZP3 were severely atrophied with disappearance of primordial follicles from ovarian cortex with an increased in the amount of oocyte-free cell clusters. Female rats immunized with Ad-rZP3 demonstrated 27% reduction of fertility. The infertility induced by Ad-rZP3 is comparatively low and ineffective. This could be due to a strong host immune response that suppresses the recombinant virus itself resulted in minimum rZP3 protein presentation to the host immune system. As a result, low antibody titers produced against rZP3 is insufficient to block oocytes from maturity and fertilization. Therefore, immunization with DrZP3 for immunocontraception is more effective than Ad-rZP3 recombinant adenovirus. It is proposed to explore further on the use of adenovirus or other alternative viruses to deliver ZP3 protein and for the development of enhanced expression of rZP3 in target host.

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 &gt;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 &gt;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.

Fertility Control in Wildlife: Review of Current Status, Including Novel and Future Technologies

Wildlife conservation requires varying degrees of management of endangered species as well as management of their potential predators and competitors. Conservation also depends on ameliorating human-wildlife conflict, especially where there is a threat to the safety of people and of their pets and livestock. In addition, sustainability of wildlife populations can be affected by feral domestic animals or invasive species, that require removal or control. With the increasing concern for animal welfare, non-lethal methods of limiting population size and distribution, such as fertility control, are gaining favor. Breeding programs in zoos depend on highly effective and selective contraception to manage sustainable insurance populations. This review covers fertility control methods currently in use, those that have not lived up to past promises, and others that are under development and present hope for addressing remaining challenges.

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.

Serum anti-Müllerian hormone dynamics in mares following immunocontraception with anti-zona pellucida or -GnRH vaccines

Circulating anti-Müllerian hormone concentration (AMH) is positively correlated to the number of small growing follicles in the mare and may reflect ovarian function. Dynamics of AMH during immunocontraception have not previously been investigated. This study aimed to compare serum AMH in mares following treatment with native porcine zona pellucida (pZP), recombinant pZP3 and pZP4 (reZP) or gonadotrophin releasing hormone (GnRH) vaccines, and saline-treated controls. Stored sera collected during two previous studies examining ovarian activity in mares during zona pellucida (ZP) or GnRH immunocontraception were analysed for serum AMH. Data were compared among treatment groups using mixed-effects linear regression and one-way ANOVA with post hoc testing. Correlations between AMH and previously reported clinical variables were estimated using Spearman's rho. Mares immunized against GnRH showed variable but detectable AMH throughout successive breeding and non-breeding seasons that were not significantly different to unvaccinated control mares. Mares treated with pZP demonstrated marked, reversible suppression of AMH. Mares immunized using reZP showed an intermediate effect. In the ZP study, AMH was positively correlated to serum progesterone concentrations, mean ovarian volumes and antral follicle counts, whereas no correlations between AMH and serum progesterone concentrations, mean ovarian volumes, or the presence of one or more follicles ≥20 mm in diameter were detected in the GnRH study. In conclusion, marked suppression of AMH during pZP immunocontraception, but not during GnRH immunocontraception, suggested enhanced suppression of ovarian follicular development and, or follicular function during pZP immunocontraception. Serum AMH concentrations may provide a novel tool for the assessment of ovarian function during ZP-based immunocontraception.

Non-surgical sterilisation methods may offer a sustainable solution to feral horse (Equus caballus) overpopulation

Feral horses are a significant pest species in many parts of the world, contributing to land erosion, weed dispersal and the loss of native flora and fauna. There is an urgent need to modify feral horse management strategies to achieve public acceptance and long-term population control. One way to achieve this is by using non-surgical methods of sterilisation, which are suitable in the context of this mobile and long-lived species. In this review we consider the benefits of implementing novel mechanisms designed to elicit a state of permanent sterility (including redox cycling to generate oxidative stress in the gonad, random peptide phage display to target non-renewable germ cells and the generation of autoantibodies against proteins essential for conception via covalent modification) compared with that of traditional immunocontraceptive approaches. The need for a better understanding of mare folliculogenesis and conception factors, including maternal recognition of pregnancy, is also reviewed because they hold considerable potential in providing a non-surgical mechanism for sterilisation. In conclusion, the authors contend that non-surgical measures that are single shot and irreversible may provide a sustainable and effective strategy for feral horse control.

COMPARISON OF CHEMICAL AND SURGICAL VASECTOMY ON TESTICULAR ACTIVITY IN FREE-ROAMING HORSES (EQUUS CABALLUS)

Free-roaming horse (Equus caballus) management is a complex issue incorporating social, economic, emotional, political, and environmental factors. Currently, few proven field techniques exist for managing free-roaming horse population growth, which can reach 20-25% annually. Although there are several strategies available for sterilizing mares when managing free-roaming horse populations, surgical vasectomy is the only method used in the field for stallions. Some managers believe that surgically vasectomizing dominant stallions would have significant effects on reducing horse populations. However, sterilizing only dominant harem stallions results in a relatively modest reduction in population growth as substantial reproduction may occur even when 100% of the dominant harem stallions are sterilized if other males perform as little as 10% of the breeding. The overall goal of the current project was to evaluate the efficacy of a novel nonsurgical method for sterilizing free-roaming horses (chemical vasectomy). In September of 2013, stallions that had been previously surgically vasectomized (SURG, n = 25), previously chemically vasectomized (CHEM, n = 16), or untreated (CONT, n = 32) were captured and surgically castrated in preparation for adoption. When comparing both sterilization methods to CONT, serum testosterone and estrone sulfate concentrations did not differ (P > 0.05), suggesting that these methods for sterilizing free-roaming stallions would not disrupt herd social hierarchy. However, similar to the CONT, all CHEM stallions had sperm present within the vas deferens seminal fluid samples. CHEM stallions had more morphologically abnormal sperm than did CONT stallions but it is not known if this affected the actual fertility. Additional research is needed using alternative sclerosing agents for chemical vasectomy in free-roaming horse populations.