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. 2026 Sep 29;12(6):e71239. doi: 10.1002/vms3.71239

Histological Findings in Testes of Baboons (Papio spp.) and Dwarf Bucks (Capra hircus) Subject to Repeated Immunisation Against GnRH

Teresa Ferrín 1,2, Eva Martínez‐Nevado 3, Juncal García 3, Adolfo Toledano‐Díaz 1, Rosario Velázquez 1, Esther Alba 1, Cristina Castaño 1, Belén Martinez‐Madrid 2, Julián Santiago‐Moreno 1,✉
PMCID: PMC13620845  PMID: 42806858

ABSTRACT

Background

Immunocontraception is a population management strategy based on vaccines that induce an immune response against reproductive targets such as GnRH.

Objectives

This study aimed to investigate spermatogenic activity in adult baboons and adult dwarf bucks subject to repeated immunisation against GnRH for extended periods.

Methods

In Experiment 1, histological findings in untreated dwarf bucks (CONTROL‐1) (n = 10) were compared with those found in males repeatedly immunised against GnRH (Improvac) during 5 years (RI‐1; n = 15). In Experiment 2, one group of baboons received immunocontraceptive treatment against GnRH during 5–10 years until death (RI‑2; n = 6). The second group received the same treatment for 10 years before discontinuation, with the interval between treatment withdrawal and death ranging from 10 to 27 months (RI‑2+S; n = 19). As in Experiment 1, testicular tissue was collected post‐mortem and processed histologically.

Results

In both species, the testicular tissue of animals treated with repeated immunisation against GnRH showed an absence of active spermatogenesis. The mean seminiferous tubule diameter in bucks was smaller in the RI‐1 group than in the CONTROL‐1 group (108.69 ± 13.17 µm vs. 187.35 ± 14.38 µm; p < 0.05). In baboons, morphometric analysis showed similar seminiferous tubule diameters in the RI‐2 (82.63 ± 4.47 µm) and RI‐2+S (79.23 ± 5.89 µm) groups.

Conclusions

In bucks and in more than 70% of baboons, the severity of degenerative changes in the germinal epithelium suggests that long‐term repeated immunisation against GnRH may lead to irreversible infertility.

Keywords: GnRH vaccine, male  immunocontraceptive, spermatogenesis, testes

Long‐term repeated immunisation against GnRH resulted in the absence of active spermatogenesis and may lead to irreversible infertility in dwarf bucks and baboons. Histological examination revealed a marked reduction of the seminiferous tubular lumen, complete depletion of germ cells, germ cell vacuolization and tubular hyalinization.

graphic file with name VMS3-12-e71239-g003.webp

1. Introduction

Wildlife contraception is a widely accepted strategy for managing populations of wild animal species, contributing to improved animal welfare (Liedholm et al. 2024). Effective reproduction management is essential for maintaining the health and well‐being of wild animals housed in zoos, particularly when high reproductive rates pose challenges related to limited space or welfare concerns. Although surgical castration of males is commonly employed to prevent unintended pregnancies and mitigate issues associated with libido and aggressive behaviour, this procedure entails surgical risks and raises ethical and welfare considerations. Consequently, alternative contraceptive strategies that provide reversible effects have been developed and implemented as suitable options (Garside et al. 2014).

In females, antiprogestagens for punctual leading to pregnancy interruption (Bigsby 1990) and progestogens for temporarily inhibiting reproductive function (Munson et al. 2002) have been widely used, albeit concern has been raised about possible pathology in progestin‐treated carnivores (Kollias 1988). Another widely used hormonal contraceptive treatment involves gonadotrophin‐releasing hormone (GnRH) agonists, such as deslorelin. Its administration, usually through subcutaneous implants, initially induces an increase in the concentrations of follicle‐stimulating hormone (FSH) and luteinising hormone (LH) (‘flare‐up effect’) followed by a suppression of the hypothalamic–pituitary–gonadal axis, by desensitisation of the GnRH receptors to GnRH, leading to inhibition of testosterone and oestrogens in males and females (Lucas 2014). For use exclusively in males, cyproterone acetate, a steroid anti‐androgen that specifically blocks the effects of androgens in all the target organs, induces reversible endocrine and spermatogenic disruption in ruminants (Flores‐Gil et al. 2020). However, prolonged administration of this drug has been associated with the development of mammary carcinomas (Spugnini et al. 2010). Finally, immunocontraception represents a relatively novel population control strategy, involving the use of vaccines that stimulate an immune response against key reproductive proteins, such as zona pellucida proteins or GnRH (Kirkpatrick et al. 1995, 1996).

Active immunisation against GnRH suppresses hypothalamic GnRH synthesis and secretion (Han et al. 2017). Consequently, LH secretion is not stimulated, leading to reduced testosterone secretion by Leydig cells. The fall of testosterone blood levels results in testicular atrophy, inhibition of spermatogenesis and impaired sperm quality (Ajadi and Oyeyemi 2015; Lincoln et al. 1982; Nuñez Favre et al. 2018). These vaccines have been investigated as an immunocontraceptive treatment in males of a wide number of both domestic (Kiyma et al. 2000; Giriboni et al. 2023; Fuchs et al. 2009) and wild species (Killian et al. 2006; Lueders et al. 2017; Schwarzenberger et al. 2022; Martinez‐Gimenez et al. 2021). Active immunisation against GnRH is particularly suitable for free‐ranging wildlife (Miller et al. 2004), and for domestic species, as well as a population control method for wildlife in zoos, where handling the animals for booster doses to prolong the initially reversible and highly effective contraceptive effect is not problematic. However, the effects of prolonged active immunisation against GnRH on spermatogenic function remain poorly characterized, and the issue of reversibility remains unsolved (Schwarzenberger et al. 2022). Sustained suppression of gonadotropin secretion over an extended period may cause severe alterations to the nuclear membrane of Sertoli cells and the mitochondrial structure of Leydig cells, as well as disruption of the germinal epithelium (Li et al. 2013), which could ultimately result in permanent infertility.

Dwarf goats (Capra hircus) are commonly found in petting zoos and are easy to handle, making them a useful experimental model for studying the effects of contraceptive treatments on testicular function in wild ruminants (Giriboni et al. 2020, 2023). Baboon species (Papio spp.) are common primates in zoos. They exhibit polygynous sexual behaviour with high testicular activity (Bercovitch 1989), making them a suitable animal model for evaluating contraceptive treatments that could be applied to other primate species. This study aimed to evaluate spermatogenic function in dwarf bucks and baboons subjected to repeated GnRH immunisation over an extended period, in order to assess the reversibility of this treatment.

2. Materials and Methods

2.1. Animals and Experimental Design

This study was conducted on adult male dwarf goats (Capra hircus) (n = 25) and baboons (Papio spp) (n = 25) housed at the Zoo Aquarium of Madrid (ZAM). In both species, repeated immunocontraception was achieved by active immunisation against GnRH using the commercial vaccine Improvac (Zoetis Inc). Animals received an initial intramuscular injection of 2 mL of Improvac containing 300 µg GnRH analog as a protein‐conjugate with diphtheria toxoid, by manual injection in goats and by manual injection in a squeeze cage or blowpipe dart injection in baboons, followed by a booster 4 weeks later and subsequent revaccinations at 6‐month intervals until either treatment cessation or death.

Individual animal data from both experiments, including age at first vaccination, age at last vaccination and the interval between the last vaccination and death, are provided in Tables S1–S2.

2.1.1. Experiment 1. Evaluation of Repeated Immunocontraceptive Treatment in Male Dwarf Goats

Histological findings in untreated animals (CONTROL‐1) (n = 10) were compared with those found in males repeatedly treated with immunocontraception during 5 years (RI‐1) (n = 15). Animals in the RI‐1 group began contraceptive treatment between 1.5 and 6 years of age. Upon natural death of all individuals, testicular tissue was retrieved for subsequent histological processing. The interval between the end of treatment and natural death ranged from 1 to 7 years.

2.1.2. Experiment 2. Evaluation of Repeated Immunocontraceptive Treatment in Male Baboons

One group of baboons received immunocontraceptive treatment against GnRH during 5–10 years until death (RI‑2; n = 6). The second experimental group received the same treatment for 10 years before discontinuation (RI‑2+S; n = 19), with the interval between treatment withdrawal and death ranging from 10 to 27 months. The length of treatment in each case was determined by the timing of natural death relative to the immunisation period. As in Experiment 1, testicular tissue was collected post‐mortem and processed histologically.

2.2. Histological and Morphometric Assessment of Testicular Tissue

Testicular tissue samples were collected by the veterinary team at ZAM following the natural death of the study animals, and processed at the Laboratory of Histology at the Department of Animal Reproduction, INIA–CSIC.

Histological samples were randomly collected from either the left or the right testis at the mid‐testicular region, after confirming the absence of asymmetry or differences in texture between testes. Samples were fixed in Bouin's solution for 24–48 h, followed by 70% ethanol before being embedded in paraffin wax. Four‐micrometer sections were obtained for histological and morphometrical evaluation and stained with standard haematoxylin and eosin. Histological and morphometrical evaluation was made using Motic Image Advanced v.3.0 software, under bright‐field microscopy (Motic BA210) at 4X, 10X and 40X magnifications. The presence of germ and somatic cells, histopathological alterations and seminiferous tubule morphometry were evaluated. For each seminiferous tubule, both major and minor diameters were measured, and 25 tubules were analysed per sample (Martínez‐Fresneda et al. 2019). Histological examination revealed limited heterogeneity among seminiferous tubules within each testis, even in samples displaying degenerative changes. Therefore, the evaluation of 25 seminiferous tubule cross‐sections was considered representative of the overall histological status of each sample.

2.3. Statistical Analysis

In both experiments, given the small sample size and the non‐normal distribution of values, statistical comparisons between groups were performed using the non‐parametric Mann–Whitney U test. All analyses were conducted using TIBCO Statistica Version 14.0, and statistical significance was set at p < 0.05. Data were expressed as the mean ± standard error of the mean (SEM).

3. Results

3.1. Efficacy of Repeated Immunocontraceptive Treatment in Male Dwarf Goats

In the CONTROL‐1 group, no histological alterations were observed in the testicular tissue of any of the animals examined. In the seminiferous epithelium, Sertoli cells were identified, along with the full range of germ cell types (spermatogonia, spermatocytes, round spermatids and elongated spermatids), as well as spermatozoa within the tubular lumen (Figure 1). Leydig cells were also observed in the interstitial space (Figure 1, left panel).

FIGURE 1.

FIGURE 1

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Testicular tissue from adult male dwarf goats in the CONTROL‐1 group, showing active spermatogenesis with the presence of spermatozoa within the lumen of the seminiferous tubules (spermatozoa, spz; Leydig cells, Lc; spermatid, sd; spermatocyte, Sc; Spermatogonia, Spg). Left: 100×. Right: 400×. Haematoxylin–eosin staining.

In the RI‐1 group, histological examination revealed a reduced tubular lumen with complete absence of germ cells (with the occasional presence of spermatogonia), or germ cells with advanced pyknosis, karyorrhexis and karyolysis. Multinucleated spermatids, vacuolization of germ cells and tubular hyalinization were also seen. These findings were consistent with severe testicular degeneration and atrophy. Neither Sertoli nor Leydig cells were detected in any of the samples (Figure 2). Furthermore, a marked increase in interstitial space with inflammatory infiltrates was observed (Figure 3). A marked interindividual variability in the degree of testicular damage was evident among bucks.

FIGURE 2.

FIGURE 2

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Histological alterations in testicular tissue of adult male dwarf goats of the RI‐1 group (repeated immunocontraception treatment). Left: Pyknosis (pk) and multinucleated spermatids (→). Right: Vacuolization (*) of the tubular epithelium. Haematoxylin–eosin staining, 100X.

FIGURE 3.

FIGURE 3

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Histological alterations in testicular tissue of adult male dwarf goats of the RI‐1 group (repeated immunocontraception treatment). Degeneration of seminiferous epithelium with inflammatory infiltrates in interstitial space (→). Haematoxylin–eosin staining, 100X.

Morphometric analysis revealed that the mean seminiferous tubule diameter was smaller in the RI‐1 group than in the CONTROL‐1 group (108.69 ± 13.17 µm vs. 187.35 ± 14.38 µm; p < 0.05).

3.2. Efficacy of Repeated Immunocontraceptive Treatment in Male Baboons

In all baboons subjected to repeated immunocontraception, histological findings were consistent: Germ cells were absent, or present only as occasional spermatogonia and spermatocytes, most of which exhibited pyknosis, karyorrhexis and karyolysis. Isolated Sertoli cells were only detected in some animals. Pronounced testicular atrophy, hyalinisation and vacuolisation of the seminiferous epithelium were observed. An increase in interstitial space accompanied by inflammatory infiltration and narrowing of the tubular lumen was also observed. No histological differences attributable to treatment suspension were detected between groups. Histological examination revealed limited heterogeneity among seminiferous tubules within each testis, as observed in bucks from the previous experiment, even in samples exhibiting severe degenerative changes. However, marked interindividual variability in the degree of testicular damage was evident among baboons, including complete hyalinisation of seminiferous tubules devoid of cells in some individuals, predominance of pyknotic cells in others, and basal hyalinization with residual spermatocytes and vacuolization in others (Figure 4). In 18 of 25 baboons (72%) of the RI‑2+S group, the damage consisted of full hyalinisation and practically acellular seminiferous ducts, compatible with irreversible damage.

FIGURE 4.

FIGURE 4

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Histological alterations in testicular tissue of adult male baboons. Left: RI‐2 group (repeated immunocontraception treatment) showing hyalinization of all seminiferous tubules (→). Right: IR‐2+S group (repeated immunization treatment followed by discontinuation) showing vacuolization of the tubules (→). These lesions were observed indistinctly in both groups. Haematoxylin–eosin staining, 100X.

Morphometric analysis revealed a mean seminiferous tubule diameter of 82.63 ± 4.47 µm in the RI‐2 group and 79.23 ± 5.89 µm in the RI‐2+S group, with no significant differences between them.

4. Discussion

These results suggest that repeated immunisation against GnRH in sexually mature bucks for at least 5 years, and in baboons for 10 years, induces irreversible contraceptive effects.

The anti‐GnRH vaccine used in this study was originally developed to suppress boar taint in swine carcasses by temporarily inhibiting spermatogenic and steroidogenic testicular function (Einarsson et al. 2009). Specifically, Improvac was developed by Zoetis to inhibit the synthesis of androstenone, the compound responsible for boar taint, and testosterone, while maintaining residual androgen levels that support growth. This treatment reduces sexual and aggressive behaviours typically observed in entire males (Dunshea et al. 2001; Zamaratskaia et al. 2008). Immunisation against GnRH acts on the hypothalamic–pituitary–testicular axis, resulting in a marked reduction in FSH and LH concentrations (Fuchs et al. 2009). This suppression leads to decreased testicular weight, reduced size of bulbourethral glands, diminished numbers of Leydig cells and an increase in sperm abnormalities, culminating in azoospermia (Einarsson et al. 2009). In a previous study, Giriboni et al. (2020) compared subcutaneous implants of the GnRH agonist deslorelin with a single immunocontraceptive treatment using Improvac (primary vaccination plus booster after 4 weeks) in adult dwarf goats. Neither treatment achieved complete azoospermia or testosterone suppression to undetectable levels, although deslorelin implants appeared to be more effective for long‐term suppression of reproductive function, as they induced a greater reduction in plasma testosterone and sperm counts. However, in that study, immunisation was limited to two doses only. Similarly, Godfrey et al. (1996) immunised feral‐origin goat bucks against GnRH using two vaccine doses, which effectively prevented the seasonal rise in FSH, LH and testosterone. This intervention resulted in reduced testicular size, diminished sexual odour and lower sperm production; however, complete azoospermia was not achieved either. To investigate whether extending treatment duration and dosage might enhance contraceptive efficacy, Giriboni et al. (2023) compared single‐dose immunocontraception (primary plus booster), repeated treatment for 3 years (primary, booster after 4 weeks and revaccinations every 6 months), and untreated controls in adult dwarf goats. The results demonstrated that 3 years of repeated immunisation markedly impaired testicular function, reducing scrotal circumference, plasma testosterone concentration, sexual odour and semen quality, but did not achieve complete suppression of spermatogenesis. Animals treated for 3 years exhibited a condition similar to that of fertile males during the non‐breeding season. Conversely, a single treatment (two doses only) failed to induce the expected contraceptive response. In the present study, repeated immunocontraceptive treatment in bucks lasted for 5 years, compared with 3 years in Giriboni et al. (2023). The extended treatment duration likely accounts for the complete suppression of spermatogenic activity observed in this study, characterised by the total absence of histologically normal germ cells, including spermatozoa, and pronounced degenerative alterations in the seminiferous tubules, such as severe atrophy, hyalinisation and vacuolisation. Inactivation of pituitary function and persistently low basal testosterone levels appear to impair Sertoli and Leydig cells, which were absent in many of the examined samples. Indeed, plasma FSH concentrations are markedly suppressed in small ruminants immunised against GnRH (Brown et al. 1994), which accounts for the impairment of Sertoli cell function and the subsequent disruption of spermatogenesis. In a previous study in ram lambs immunised against GnRH, histological analysis revealed testicular atrophy and a reduction in seminiferous tubule diameter, along with the absence of spermatozoa in many treated animals (Kiyma et al. 2000). However, all of these pathological changes were less severe than those observed in the bucks subjected to repeated immunisation in our study. These findings suggest that complete contraception in ruminants requires prolonged and repeated immunisation to fully suppress spermatogenic activity.

Our findings in baboons were consistent with observations in male giraffes (Giraffa camelopardalis) treated with repeated immunisation against GnRH for over 2 years, where faecal testosterone levels and testicular size failed to return to pre‐treatment values even after 4 years of treatment suspension (Schwarzenberger et al. 2022). In African elephants (Loxodonta africana), repeated GnRH vaccination over 2–4 years has yielded promising results (Lueders et al. 2017), with a 40% reduction in testicular size at the end of treatment and azoospermic or immotile ejaculates after the first year. A review of published and unpublished studies in African elephants concluded that irreversible effects may occur after more than 2–3 years of repeated treatment (4–8 doses), with male age at first treatment influencing the likelihood of reversibility, at least in relation to androgen‐dependent behaviours (Bertschinger and Lueders 2018).

Taken together, available evidence suggests that the duration of repeated immunisation against GnRH treatment required to induce irreversible contraception varies between species: about 10 years in baboons in the current study, 5 years in dwarf goats and as little as 3 years in giraffes. However, only limited studies have been conducted, largely due to the inherent challenges of carrying out long‐term immunocontraception trials in wild species. Further research is therefore needed to inform population management strategies in zoos and wildlife reserves.

It is noteworthy that most immunocontraception studies have assessed treatment efficacy using plasma or faecal testosterone levels, testicular and accessory gland size, and semen quality. Histological evaluation of testicular damage, however, has rarely been reported and represents the most objective assessment of spermatogenic activity. After a single‐course immunisation (primary plus booster) in pigs, histological alterations of the germinal epithelium and Leydig cells have been observed (Einarsson et al. 2009), while in broiler cockerels a reduction in germinal epithelium height has been described (Wang et al. 2019). To our knowledge, the present study is the first to conduct a comprehensive histological and morphometric evaluation of testicular tissue following long‐term repeated immunocontraception. Our findings suggest that the period of treatment required for complete disruption of spermatogenesis varies according to the species. Therefore, it is recommended that zoos employing immunocontraception for population control should systematically preserve testicular tissue after the death of treated animals, in order to enable subsequent histological and morphometric studies.

5. Conclusions

The severity of degenerative changes in the germinal epithelium suggests that repeated immunisation against GnRH for a long time may induce irreversible infertility in dwarf bucks and baboons. Because this repeated treatment ultimately arrests spermatogenesis, it is considered an effective contraceptive treatment. Both species were used as experimental animal models; therefore, a comparable physiological response can be anticipated in other bovid and primate species. Histological assessment of spermatogenic activity is recommended in deceased zoo animals subjected to contraceptive treatments to objectively evaluate the irreversibility of the treatments.

Author Contributions

Teresa Ferrín : writing – original draft, methodology, formal analysis. Eva Martínez‐Nevado : conceptualization, investigation, methodology, validation, writing – review and editing, resources. Juncal García : investigation, methodology, validation, resources. Adolfo Toledano‐Díaz : investigation, methodology, validation, writing – review and editing. Rosario Velázquez : methodology, validation. Esther Alba : methodology, validation, formal analysis. Cristina Castaño : methodology, validation. Belén Martinez‐Madrid : investigation, writing – original draft, methodology, validation, writing – review and editing, formal analysis, data curation, supervision. Julián Santiago‐Moreno : conceptualization, investigation, funding acquisition, writing – review and editing, project administration, data curation, supervision.

Funding

This study was funded through the Research and Development Agreement between Fundación Parques Reunidos and INIA–CSIC (Ref. CID24‐207). Part of this study was supported by the project PID2023‐146957OB‐I00, funded by MICIU/AEI/10.13039/501100011033 and FEDER UE.

Ethics statement

All animals were managed in ways consistent with the Spanish Policy for Animal Protection (RD53/2013), which conforms to European Union Directive 86/609 regarding the protection of animals used in scientific experiments. All procedures of this study were evaluated and approved by the internal animal welfare committee based on the EAZA (European Association of Zoos and Aquariums) Code of Ethics.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: vms371239‐sup‐0001‐SuppMat.docx.

VMS3-12-e71239-s001.docx (22KB, docx)

Data Availability Statement

The data that support the findings of this study are openly available in Supplementary Data: Histological Images of Testes from GnRH‐ at http://hdl.handle.net/10261/440090.

References

  1. Ajadi, T. , and Oyeyemi M.. 2015. “Short‐term Effects of a Single Dose of Gonadotrophin Releasing Hormone (GnRH) Vaccine on Testicular and Ejaculate Characteristics of Dogs.” Bulgarian Journal of Veterinary Medicine 18: 123–131. 10.15547/bjvm.809. [DOI] [Google Scholar]
  2. Bercovitch, F. B. 1989. “Body Size, Sperm Competition, and Determinants of Reproductive Success in Male Savanna Baboons.” Evolution; International Journal of Organic Evolution 43, no. 7: 1507–1521. 10.1111/j.1558-5646.1989.tb02600.x. [DOI] [PubMed] [Google Scholar]
  3. Bertschinger, H. J. , and Lueders I.. 2018. “Use of Anti‐Gonadotropin‐Releasing Hormone Vaccines in African Elephants (Loxodonta africana): A Review.” Bothalia 48, no. 2: 1–9. 10.4102/abc.v48i2.2320. [DOI] [Google Scholar]
  4. Bigsby, R. M. 1990. “Progestins and Antiprogestins: A Review of Their Role in Medicine and Bioassays Used in Their Development.” Alternatives to Laboratory Animals 18, no. 1 pt. 1: 301–311. 10.1177/026119299001800130.1. [DOI] [Google Scholar]
  5. Brown, B. W. , Mattner P. E., Carroll P. A., et al. 1994. “Immunization of Sheep Against GnRH Early in Life: Effects on Reproductive Function and Hormones in Rams.” Reproduction 101, no. 1: 15–21. 10.1530/jrf.0.1010015. [DOI] [PubMed] [Google Scholar]
  6. Dunshea, F. R. , Colantoni C., Howar K., et al. 2001. “Vaccination of Boars With a GnRH Vaccine (Improvac) Eliminates Boar Taint and Increases Growth Performance1.” Journal of Animal Science 79, no. 10: 2524–2535. 10.2527/2001.79102524x. [DOI] [PubMed] [Google Scholar]
  7. Einarsson, S. , Andersson K., Wallgren M., Lundström K., and Rodriguez‐Martinez H.. 2009. “Short‐ and Long‐Term Effects of Immunization Against Gonadotropin‐Releasing Hormone, Using Improvac, on Sexual Maturity, Reproductive Organs and Sperm Morphology in Male Pigs.” Theriogenology 71, no. 2: 302–310. 10.1016/j.theriogenology.2008.07.022. [DOI] [PubMed] [Google Scholar]
  8. Flores‐Gil, V. N. , Velázquez R., Toledano‐Díaz A., Santiago‐Moreno J., and López‐Sebastián A.. 2020. “Short Term Administration of Cyproterone Acetate for Contraception: Effects on Testosterone Secretion and Semen Characteristics in Rams (Ovis aries) and Bucks (Capra hircus).” Spanish Journal of Agricultural Research 18, no. 4: e0407. 10.5424/sjar/2020184-16871. [DOI] [Google Scholar]
  9. Fuchs, T. , Thun R., Parvizi N., et al. 2009. “Effect of a Gonadotropin‐Releasing Factor Vaccine on Follicle‐Stimulating Hormone and Luteinizing Hormone Concentrations and on the Development of Testicles and the Expression of Boar Taint in Male Pigs.” Theriogenology 72, no. 5: 672–680. 10.1016/j.theriogenology.2009.04.025. [DOI] [PubMed] [Google Scholar]
  10. Garside, D. , Gebril A., Alsaadi M., and Ferro V. A.. 2014. “Fertility Control in Wildlife: Review of Current Status, Including Novel and Future Technologies.” In Reproductive Sciences in Animal Conservation. Progress and Prospects, edited by Holt W.V., Brown J.L., and Comizzoli P., 467–488. Springer Nature. [DOI] [PubMed] [Google Scholar]
  11. Giriboni, J. , Lacuesta L., Santiago‐Moreno J., and Ungerfeld R.. 2020. “Chronic Use of a GnRH Agonist (Deslorelin) or Immunization Against GnRH: Effects on Testicular Function and Sperm Quality of Bucks.” Domestic Animal Endocrinology 71: 106395. 10.1016/j.domaniend.2019.106395. [DOI] [PubMed] [Google Scholar]
  12. Giriboni, J. , Martínez‐Nevado E., García J., et al. 2023. “Single or Repeated Immunization Against GnRH Fails to Completely Abolish Spermatogenesis in Dwarf Bucks (Capra hircus).” Zoo Biology 42, no. 3: 364–370. 10.1002/zoo.21743. [DOI] [PubMed] [Google Scholar]
  13. Godfrey, S. I. , Walkden‐Brown S. W., Martin G. B., and Speijers E. J.. 1996. “Immunisation of Goat Bucks Against GnRH to Prevent Seasonal Reproductive and Agonistic Behaviour.” Animal Reproduction Science 44, no. 1: 41–54. 10.1016/0378-4320(96)01479-0. [DOI] [Google Scholar]
  14. Han, X. , Zhou Y., Zeng Y., et al. 2017. “Effects of Active Immunization Against GnRH Versus Surgical Castration on Hypothalamic–Pituitary Function in Boars.” Theriogenology 97: 89–97. 10.1016/j.theriogenology.2017.04.038. [DOI] [PubMed] [Google Scholar]
  15. Killian, G. , Miller L., Rhyan J., and Doten H.. 2006. “Immunocontraception of Florida Feral Swine With a Single‐Dose GnRH Vaccine.” American Journal of Reproductive Immunology 55, no. 5: 378–384. 10.1111/j.1600-0897.2006.00379.x. [DOI] [PubMed] [Google Scholar]
  16. Kirkpatrick, J. F. , Calle P. P., Kalk P., Liu I. K. M., and Turner J. W.. 1996. “Immunocontraception of Captive Exotic Species. II. Formosan Sika Deer (Cervus nippon taiouanus), Axis Deer (Cervus axis), Himalayan Tahr (Hemitragus jemlahicus), Roosevelt Elk (Cervus elaphus Roosevelti), Reeves' Muntjac (Muntiacus reevesi), and Sambar Deer (Cervus unicolor).” Journal of Zoo and Wildlife Medicine 27, no. 4: 482–495. [Google Scholar]
  17. Kirkpatrick, J. F. , Zimmermann W., Kolter L., Liu I. K. M., and Turner J. W. Jr. 1995. “Immunocontraception of Captive Exotic Species. I. Przewalski's Horses (Equus przewalskii) and Banteng (Bos javanicus).” Zoo Biology 14, no. 5: 403–416. 10.1002/zoo.1430140503. [DOI] [Google Scholar]
  18. Kiyma, Z. , Adams T. E., Hess B. W., Riley M. L., Murdoch W. J., and Moss G. E.. 2000. “Gonadal Function, Sexual Behavior, Feedlot Performance, and Carcass Traits of Ram Lambs Actively Immunized Against GnRH.” Journal of Animal Science 78, no. 9: 2237–2243. 10.2527/2000.7892237x. [DOI] [PubMed] [Google Scholar]
  19. Kollias Jr., G. V. 1988. “Complications of Progestogen Contraception in Exotic Felids.” Proceedings of the American Association of Zoo Veterinarians—Journal of Zoo and Wildlife Medicine 20: 149–152. [Google Scholar]
  20. Li, Y. , Liu Y., Su S., Pu Y., Zhang X., and Fang F.. 2013. “Immunization Against Recombinant GnRH‐I Alters Testicular Structure in an Experimental Boar Model.” Zygote 23, no. 1: 125–135. 10.1017/S0967199413000397. [DOI] [PubMed] [Google Scholar]
  21. Liedholm, S. E. , Hecht L., and Elliott V.. 2024. “Improving Wild Animal Welfare Through Contraception.” Bioscience 2024, no. 74: 695–700. 10.1093/biosci/biae071. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Lincoln, G. A. , Fraser H. M., and Fletcher T. J.. 1982. “Antler Growth in Male Red Deer (Cervus elaphus) After Active Immunization Against LH–RH.” Reproduction 66: 703–708. 10.1530/jrf.0.0660703. [DOI] [PubMed] [Google Scholar]
  23. Lucas, X. 2014. “Clinical Use of Deslorelin (GnRH Agonist) in Companion Animals: A Review.” Reproduction in Domestic Animals 49, no. S4: 64–71. 10.1111/rda.12388. [DOI] [PubMed] [Google Scholar]
  24. Lueders, I. , Young D., Maree L., et al. 2017. “Effects of GnRH Vaccination in Wild and Captive African Elephant Bulls (Loxodonta africana) on Reproductive Organs and Semen Quality.” PLoS ONE 12, no. 9: e0178270. 10.1371/journal.pone.0178270. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Martínez‐Fresneda, L. , O'Brien E., Velázquez R., et al. 2019. “Seasonal Variation in Sperm Freezability Associated With Changes in Testicular Germinal Epithelium in Domestic (Ovis aries) and Wild (Ovis musimon) Sheep.” Reproduction, Fertility and Development 31, no. 10: 1545–1557. 10.1071/RD18511. [DOI] [PubMed] [Google Scholar]
  26. Martinez‐Gimenez, J. , Ferrero‐Vicente L., and Feltrer‐Rambaud Y.. 2021. “Effects of a GnRH Vaccine (Improvac) on Patagonian (Otaria byronia) and California Sea Lions (Zalophus californianus).” Journal of Zoo and Wildlife Medicine 52, no. 2: 721–725. 10.1638/2019-0098. [DOI] [PubMed] [Google Scholar]
  27. Miller, L. A. , Rhyan J., and Killian G. K.. 2004. “GonaCo, a Versatile GnRH Contraceptive for a Large Variety of Pest Animal Problems.” In Proceedings of the Vertebrate Pest Conference , Division of Agriculture and Natural Resources, edited by Timm R.M. and Gorenzel W. P., 269–273. University of California. [Google Scholar]
  28. Munson, L. , Gardner I. A., Mason R. J., Chassy L. M., and Seal U. S.. 2002. “Endometrial Hyperplasia and Mineralization in Zoo Felids Treated With Melengestrol Acetate Contraceptives.” Veterinary Pathology 39, no. 4: 419–427. 10.1354/vp.39-4-419. [DOI] [PubMed] [Google Scholar]
  29. Nuñez Favre, R. , García M. F., García Mitacek M. C., et al. 2018. “Reestablishment of Sperm Quality After Long‐Term Deslorelin Suppression in Tomcats.” Animal Reproduction Science 195: 302–308. 10.1016/j.anireprosci.2018.06.008. [DOI] [PubMed] [Google Scholar]
  30. Schwarzenberger, F. , Krawinkel P., Jeserschek S.‐M., et al. 2022. “Immunocontraception of Male and Female Giraffes Using the GnRH Vaccine Improvac.” Zoo Biology 41, no. 1: 50–64. 10.1002/zoo.21651. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Spugnini, E. P. , Mezzanotte F., Freri L., Betti G., Citro G., and Baldi A.. 2010. “Cyproterone Acetate‐Induced Mammary Carcinoma in Two Male Cats.” Journal of Feline Medicine and Surgery 12, no. 6: 515–516. 10.1016/j.jfms.2010.01.009. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Wang, C. , Zeng Y. T., Chen X. Y., et al. 2019. “Improvac Induces Immunocastration by Affecting Testosterone Levels and Disrupting Spermatogenesis in Male Broiler Chickens.” Poultry Science 98, no. 11: 6034–6045. 10.3382/ps/pez228. [DOI] [PubMed] [Google Scholar]
  33. Zamaratskaia, G. , Andersson H., Chen G., Andersson K., Madej A., and Lundström K.. 2008. “Effect of a Gonadotropin‐Releasing Hormone Vaccine (Improvac) on Steroid Hormones, Boar Taint Compounds and Performance in Entire Male Pigs.” Reproduction in Domestic Animals 43, no. 3: 351–359. 10.1111/j.1439-0531.2007.00914.x. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supporting File: vms371239‐sup‐0001‐SuppMat.docx.

VMS3-12-e71239-s001.docx (22KB, docx)

Data Availability Statement

The data that support the findings of this study are openly available in Supplementary Data: Histological Images of Testes from GnRH‐ at http://hdl.handle.net/10261/440090.

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