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As part of the Reproductive Control Methods Project, the USDA National Wildlife Research Center (NWRC) has developed multiple non-lethal contraceptive tools to control population of over-abundant wildlife species. Working in conjunction with Dr. G. P. Talwar of the Talwar Research Institute in India, scientists at NWRC have shown that a recombinant form of GnRH peptide has successfully contracepted swine. Feral swine not only pose a significant agricultural issue due to over-population; they act as a reservoir for Brucella suis, a threat to domestic livestock and humans. The Brucella abortus RB51 (Rough Brucella) vaccine, developed for bovine brucellosis and licensed by the USDA Animal Plant Health Inspection Service, has shown protection for some swine and is also effective against Brucella suis infection and other antigens. There is currently no approved vaccine for swine brucellosis (feral or domestic) in the United States. Past studies performed at The Ohio State University show that Brucella suis vaccination appears to protect against abortion and colonization in pigs after a virulent challenge. The Talwar recombinant peptide consists of 5 LHRH peptides interspersed with 4 universally immunogenic “promiscuous” T-cell epitopes of diverse genetic background. By transforming the Brucella suis strain with the Talwar recombinant LHRH plasmid, the bacteria will produce both its own host proteins, and the LHRH protein. A systemic immune response should then be generated to the Brucella suis proteins being produced, allowing for vaccination to Brucella suis. In addition, an immune response would be generated to the LHRH proteins resulting in antibody production and immunocontraception. A broad range of applications can be proposed utilizing the recombinant LHRH, such as other dual vaccines and scale-up production of a low-cost single-injection LHRH vaccine.

GonaConTM is a single-shot immunocontraceptive vaccine that targets the reproductive hormone gonadotropin releasing hormone (GnRH). The GnRH peptide used in the vaccine is secreted by the hypothalamus of the brain and is specifically known as luteinizing hormone releasing hormone. This peptide stimulates the synthesis and secretion of luteinizing hormone and follicle stimulating hormone by the anterior pituitary gland. These hormones in turn stimulate hormone and gamete production by the ovary. In earlier studies with deer, we showed that antibodies produced in response to a single shot of GonaCon inactivated endogenous GnRH and greatly reduced fertility, reproductive steroids, and associated behaviors for at least 2 years. In the present study, we report on contraceptive efficacy and behavioral observations up to 6 years after female white-tailed deer were given a single shot of one of several formulations of GonaCon. We compared the standard GonaCon made by conjugating the GNRH peptide to keyhole limpet hemocyanin (GonaCon-KLH) to one with the GnRH peptide conjugated to a blue mollusk protein (GonaCon-Blue) and to a 2-shot regimen with GonaCon-KLH. All GonaCon preparations were made into an emulsion with AdjuVacTM and administered to 5 mature female deer per treatment. The results showed that the GonaCon-Blue preparation significantly out-performed the other single-shot vaccines, as well as the 2-shot regimen of GonaCon-KLH, with efficacy of 80-100% for each of the 5 years in the study. Interestingly, expression of estrous behavior was minimal in Years 1-2 following treatment for all groups, but expression of estrus increased in later years of the study, even though does remained infertile. This expression of estrus and fertility was reversed with follicle stimulating hormone releasing hormone (FSH-RH) peptide conjugated to a mollusk protein and mixed as an emulsion with AdjuVac. This suggests that does possess an FSH-RH peptide, secreted by the hypothalamus, which modulates follicle development and resulting estrogen production and reproductive behavior.

Greater demand for non-lethal means of alleviating human-wildlife conflict has led to an interest in contraception as a wildlife management tool. The development of a single-injection Gonadotropin-Releasing Hormone (GnRH) contraceptive vaccine by the USDA National Wildlife Research Center reduces logistical limitations and the cost of using a vaccine that requires 2 injections. This study assesses the efficacy of different GnRH-KLH (keyhole limpet hemocyanin) vaccine designs. Forty-two captive female black-tailed deer were divided into 3 groups. A control group was injected with saline solution, and 2 treated groups were given either GonaCon™, a GnRH vaccine paired with AdjuVac™ (an adjuvant containing 175 µg of killed Mycobacterium avium), or GnRH vaccine without AdjuVac™ (instead substituting DEAE-dextran/oil (DD) as the adjuvant). Pregnancy rates in deer treated with GonaCon™ were significantly reduced as compared to saline controls (P = 0.006). There was no significant difference between GnRH-DD compared to saline (P = 0.297). Significant difference was found between GonaCon™ and GnRH-DD (P = 0.055). Vaccinated does that remained fertile received booster injections according to treatment group and were administered either GonaCon™ containing 87 µg M. avium or GnRH-KLH conjugate bound to DEAE-dextran. Deer that received booster injections regardless of the adjuvant were 100% contracepted for 1 year. Six out of 10 deer that received a prime injection of GonaCon™ remained 100% contracepted for 3 years, suggesting that the killed M. avium in the adjuvant is essential for the success of GonaCon™ as a single-injection GnRH vaccine.

Transmissible diseases among wildlife species, and between wildlife and domestic livestock, are a matter of increasing concern. A combination of approaches should be considered for controlling disease transmission. If a vaccine is available or can economically be developed for the disease, it should be used as the primary component of the disease management strategy. For example, development of an oral rabies vaccine has led to programs where baits are dispersed on a large scale in a barrier zone to prevent the spread of rabies. However, there are no vaccines available for many diseases and incentives are frequently not present for their development. Because disease transmission is often a function of population density, culling is sometimes used to slow or prevent the spread of a disease. This technique also has disadvantages, because it can lead to an influx of new diseased animals, and because populations generally rebound quickly. Fertility control has been suggested as a management option for slowing disease transmission. Reproductive technology which lowers the population but which also reduces or eliminates reproductive behavior could be used to minimize contact among animals. Physical contact during mating may increase disease transmission by traditional oral, pulmonary and nasal routes. For some wildlife diseases, such as brucellosis and pseudorabies, there is evidence that transmission in also venereal. For these wildlife diseases, fertility control could potentially reduce disease transmission and be a very effective tool for preventing disease transmission.

GonaCon™ Immunocontraceptive Vaccine targets the reproductive hormone gonadotropin releasing hormone (GnRH) secreted by the hypothalamus of the brain. Antibodies produced in response to the vaccine inactivate endogenous GnRH, which in turn eliminates stimulation of the pituitary gland and gonads in males or females. The resulting “immunocastration” renders animals unable to produce reproductive steroids or gametes. In previous studies, we demonstrated that GonaCon™ was effective in impairing fertility for up to 3 years in female deer without apparent side effects. However, detailed post mortem evaluations were not done. To better understand the entire physiological response of deer to GonCon™ and to establish if contraindications were associated with its use, we undertook the present study. To evaluate toxicity and safety, 7 does were given the standard single injection GnRH-KLH vaccine dose (1000 µg) delivered IM in 1 ml using AdjuVac™ adjuvant and compared to 6 does given a single control saline IM injection and 6 does given 3 injections of GonaCon™ at 2-week intervals per dose. The study was conducted for 20 weeks. Does were blocked by weight and randomly assigned within blocks to treatment groups. Blood samples were drawn immediately prior to vaccination and at 5, 10, 15, and 20 weeks post immunization. Blood was assayed for LH, testosterone and progesterone, and anti-GnRH titers, as well as hematology and blood chemistry. At each sampling period, the general health of the doe was observed and the injection site was inspected for the formation of abscesses or other tissue reactions. At Week 20, all deer were euthanized and evaluated at necropsy by veterinary pathologists and samples of lymph nodes, reproductive organs, lung, liver, heart, kidney, spleen, and brain were taken for histology. Aside from granulomata formation at the injection site, there were no significant contraindications or toxic effects associated with GonaCon™.

Avian contraception is a nonlethal management tool that can be utilized in conjunction with other management techniques to help manage bird populations causing damage. Because management situations vary with respect to the type of damage, species involved, location, and nontarget hazards, it is necessary to develop multiple contraceptive tools to allow management flexibility. DiazaCon™ and nicarbazin have already been developed at the National Wildlife Research Center as avian contraceptives. Although both of these are promising contraceptive agents, more are needed for a wider variety of situations. Current research is focusing on other cholesterol inhibitors, inhibitors of the P450 side chain cleavage enzyme, and aromatase inhibitors. Because cholesterol is needed for steroid reproductive hormone production, inhibition of cholesterol impairs reproduction by preventing the formation of the necessary hormones. The P450 side chain cleavage enzyme is needed to convert cholesterol to pregnenolone, the precursor to progesterone and testosterone. Progesterone is needed for egg formation, ovulation, and oviposition, and testosterone is needed for sperm production. Aromatase is needed to convert testosterone to estradiol, which is needed in females to stimulate the production of egg yolk precursors in the liver. Inhibition of either of these enzymes should result in impaired reproduction. In the future, natural plant products with contraceptive activity, such as neem seed, will also be investigated. Because development of avian contraceptives is time intensive, an efficient screening process needs to be in place. Population models can assist in choosing specific agents to test for a given species and management situation. Although contraception is unlikely to be useful as a stand-alone tool, it can be included in integrated management plans.

Despite the fact that many wildlife species have become overabundant both in North America and other parts of the world, the public is increasingly unwilling to manage wildlife populations with traditional techniques such as trapping or lethal methods. A growing segment of the public is urging the use of contraceptives to reduce populations of overabundant free-ranging wildlife. In spite of public pressure, the development and use of wildlife fertility control techniques has been slow to occur, partially because of the difficulty in developing efficient, cost-effective methods, and partially because of misconceptions about these potential techniques. The regulatory authority for contraceptives has recently been moved from the Food and Drug Administration (FDA) to the Environmental Protection Agency (EPA); the extensive EPA registration process is both rigorous and costly. Only one wildlife contraceptive is currently registered and available: the National Wildlife Research Center (NWRC) worked to develop a product for reducing the hatchability of Canada goose eggs in cooperation with Innolytics, LLC, who holds the registration for OvoControl® G. Development is continuing for additional experimental products. Another product developed by the NWRC, the single-shot GonaCon™ Immunocontraceptive Vaccine is poised to begin the registration process. A third product, DiazaCon™, will be soon tested for field efficacy and should begin the registration process within the year. No single wildlife contraceptive technique would be applicable for use in all wildlife species and for all management situations for a particular species. Differences in animal physiology and behavior, as well as differences in the ecology of the damage, affect which contraceptives will be most effective. Therefore, contraceptives with different modes of action will need to be developed for different species and uses. Wildlife contraceptives will not replace other management tools and will probably have a limited use, primarily in urban/suburban areas. In most species, wildlife contraceptives will not rapidly reduce populations. Populations of short-lived species such as rodents could be rapidly reduced with contraceptives; however, in long-lived species such as deer and horses, it would take years to reduce populations with fertility control alone, and damage caused by those species will continue to occur. This manuscript will discuss what contraceptive techniques are being developed by the USDA Wildlife Services NWRC, and when, where, and for what species they may be applicable.

Expanding populations of resident Canada geese that remain in suburban and urban areas year-round often result in increased conflicts with humans. Non-lethal and humane means are needed for managing the size of Canada goose flocks residing near or on airports, golf courses, industrial parks, government sites, and city parks. A side effect of nicarbazin, a veterinary drug used to control coccidiosis in chickens, is decreased egg production and hatching. Exploiting this side effect, studies of nicarbazin for reducing the hatchability of eggs from Canada geese were conducted. An initial study in Cotumix quail verified reduction in hatchability in a species other than chickens. Because plasma nicarbazin was not routinely measured, a study in chickens was conducted to determine the relationship between plasma and egg nicarbazin. A comparative study in chickens, mallards, and Canada geese showed that nicarbazin absorption was lowest in geese. Studies in both penned and wild Canada geese showed that reduction in hatchability was possible but neither study used bait suitable for general field application. Bait development led to the OvoControl-G® (Innolytics LLC) bait, which resulted in reduction in hatchability of 51% at treated sites compared to control sites in the field. Previous studies showed that nicarbazin is practically non-toxic and is environmentally friendly; timing and management of baiting will minimize non-target hazards. OvoControl-G® 2500 ppm nicarbazin bait is recommended for incorporation into a comprehensive management plan as a reproductive inhibitor for use in controlling resident Canada goose flock sizes.

Due to increasing human-wildlife conflicts with birds and growing opposition to lethal techniques, nonlethal methods need to be developed to help manage bird populations. DiazaCon™ is a promising oral contraceptive that acts by directly inhibiting the conversion of desmosterol to cholesterol. Because cholesterol is essential for the production of the steroid reproductive hormones testosterone, progesterone, and estradiol, DiazaCon™ also indirectly inhibits the formation of these hormones. These hormones are essential for sperm and egg production, and the production of egg yolk precursors in the liver. Because DiazaCon™ is cleared slowly from the liver, its contraceptive effects are long-lasting. Initial research with Coturnix quail (Coturnix coturnix) helped determine DiazaCon's mechanism of action. Further research showed efficacy in monk parakeets (Myiopsitta monachus) and mallards (Anas platyrhynchos). Brown-headed cowbirds (Molothrus ater), American crows (Corvus brachyrhynchos) and ring-necked doves (Streptopelia risoria) were also studied as potential candidates for DiazaCon™ contraception. Mallards and ring-necked doves were used as model species for Canada geese (Branta canadensis) and pigeons (Columba livia), respectively. DiazaCon™ application over a very short time results in long-lasting contraceptive effects, an advantage for target species, but a disadvantage for nontarget species. Care must be taken when delivering DiazaCon™ to determine what nontargets are present and how best to avoid them. Timing of delivery is also critical to ensure maximal reproductive effects, and information on the reproductive cycles of the species of interest is needed.

As part of the program to develop contraceptive tools to control populations of over-abundant wildlife species, the NWRC has developed a single-injection gonadotropin-releasing hormone (GnRH) immunocontraceptive vaccine, GonaCon™. GonaCon™ has been tested and shown to provide contraceptive effects lasting 1-3 years in many pest species including white-tailed deer, domestic and feral pigs, bison, wild horses, cats, dogs, and California ground squirrels. GonaCon™ contains a GnRH peptide conjugated to keyhole limpet hemocyanin combined with AdjuVac™, an adjuvant also developed at the USDA National Wildlife Research Center. Immunization against GnRH prevents the circulating GnRH from stimulating the release of pituitary luteinizing hormone and follicle-stimulating hormone. This process of immuno‑neutralization of GnRH effects a temporary non‑surgical castration in both males and females. Contraceptive and behavioral effects of GonaCon™ are discussed for a variety of species.

Overpopulation of feral horses in several western states is an unquestioned problem. Current management strategies of removal and adoption are expensive, logistically challenging, and ineffective as a means of population control. We are testing three long-acting contraceptive approaches on feral Nevada mares. Modified reversible immunocontraceptive vaccines for gonadotropin releasing hormone (GnRH) and porcine zona pellucida (PZP) (SpayVac), and intrauterine contraceptive devices (IUDs), are being evaluated to determine: 1) their safety and efficacy for preventing pregnancy for multiple years, 2) whether the effects are reversible, and 3) whether there are notable contraindications. Preliminary data after 1 year suggest that IUD- and PZP-treated mares continue to exhibit breeding and estrus, while GnRH-treated mares are less likely to cycle. All mares in the GnRH and PZP treatments were infertile for the breeding season. Eighty percent of the IUD-treated mares were infertile; those mares that became pregnant likely failed to retain the IUD. A notable contraindication was that uterine edema normally observed in mares in the follicular phase of the estrous cycle was commonly observed in PZP-treated mares. Because administration of each contraceptive approach is different, and each has different effects and expected duration, one approach or a combination of approaches may be best suited for specific field applications. Subsequent years of this study should establish the efficacy and safety of one or more long-acting contraceptive approaches for feral horse population control.

Populations of wildlife, such as California ground squirrels, can grow to the extent that they come in conflict with humans. Contraception is a method of population management under investigation that may be useful in situations where neither leaving the animals uncontrolled nor lethal control are apropos. In this study, we tested the use of a single-injection gonadotropin releasing hormone (GnRH) immunocontraceptive vaccine in urban California ground squirrels. We monitored the effects of treatment for two breeding seasons. Immunization reduced the proportion of females lactating by 91% the first year and 96% in the second year. Testicular development was inhibited 35% the first year and 89% the second year. There is a delay of several months from the time of injection to inhibition of testes development. Reduction in the number of juveniles born per adult as determined by a visual count index was 9% the first year and 66% the second year. This study shows that the single-shot GnRH vaccine is over 90% effective for at least 1.5 years and requires several months after immunization for contraceptive effect. Because the immunization requires injection, it is labor intensive, but it is much more practical than treatments requiring multiple administrations to the same animal. GnRH immunocontraception may be a useful tool in rodent population management in certain circumstances.

We determined the effect of a GnRH vaccine on reproductive function of sexually mature 5-month female and male domestic swine. The vaccine, GonaCon™, developed at NWRC contains a GnRH peptide conjugated to KLH, combined with AdjuVac™ adjuvant also developed at NWRC. Four groups of ten females were given single IM immunizations either of 800μg GnRH vaccine, 1600μg GnRH vaccine, a prime and boost of 400μg GnRH vaccine and a sham dose adjuvant alone (control). At 8 months old, females were evaluated daily for estrus and bred by artificial insemination if in standing heat. Females not showing heat after 60 days were considered infertile. Farrowing data were collected for bred females ~115days later. All control gilts showed heat and became pregnant, whereas none given the dual 400μg dose showed heat or were bred. Of the 10 gilts receiving 800μg GnRH vaccine 3 were bred, but only 2 became pregnant. For gilts receiving 1600μg, 1 showed heat and became pregnant. Serum antibody titers were non-detectable in the control group, highest in gilts receiving 2x-400μg, followed by 1600μg and 800μg treatments. Titers were inversely correlated to suppression of estrus and fertility. Groups of five boars received either adjuvant only, 1 x- 800μg or 1600μg, or 2x- 400μg GnRH vaccine IM. Blood and scrotal testicular measurements were taken initially and 4 and 16 week post-treatment. Testicular size and serum testosterone decreased in all groups except controls and was inversely related to serum antibody titers. The authors conclude that; injectable GnRH vaccine is effective for contraception of swine.

PZP and GnRH immunocontraceptive vaccines were each tested in white-tailed deer (Odocoileus virginianus) . Vaccination with PZP produced reversible infertility lasting 1 to 4 years. The first two years of active immunization resulted in an 89% reduction in fawning. Reduction in fawning for the 7-year study containing 4 years of no boosting was 72%. PZP immunization resulted in multi-estrus behavior, with contracepted deer returning to estrus up to 7 times. A five year study of GnRH immunization was conducted in both male and female deer. Treatment of does led to reduced fawning rates, reduced estrus behavior and reduced concentrations of progesterone. During active immunization GnRH does bred to untreated bucks had an 88% reduction in fawning caused by either immunocontraception or immunocontragestion. Reduction in fawning for the 5 year study containing 2 years of no boosting was 74%. The vaccine effect was reversible and directly related to the antibody titer. Infertility lasted up to two years without boosting. GnRH immunized bucks had no interest in sexual activity when paired with control females. Depending on the immunization schedule, antlers either dropped early or remained in velvet.

Research on a PZP contraceptive vaccine was performed at 2 sites; Penn State University and Seneca Army Depot in upper New York. The Penn State study included immune response, hormone analysis, fawning and behavioral analysis. The Seneca depot studied behavioral and fawning response in a semi-free ranging setting. At Penn State University, in a 7 year study, does were actively immunized for two years resulting in a 90% reduction in fawns. They were followed for 5 more years to determine if the effect was reversible. The reduction in fawning over the 7 years was 72%. Most deer returned to fertility with a single fawn common as the antibody titer dropped . In a two year study at Seneca depot, the deer were vaccinated by darting after coming to a bait station. The reduction in fawning over the two years was 91%, and the number of does giving birth decreased 86%. The effects of PZP immunization depend on the magnitude of the immune response. During active immunization, ovulation is prevented (low progesterone levels). A lower immune response allows ovulation, but sufficient antibody is available to block sperm penetration of the oocyte. When antibody levels are insufficient to block sperm binding, reproduction rates return to normal.