Permanent contraception of dogs induced with intratesticular injection of a Zinc Gluconate-based solution

Male animal sterilization: history, current practices, and potential methods for replacing castration

Sterilization and castration have been synonyms for thousands of years. Making an animal sterile meant to render them incapable of producing offspring. Castration or the physical removal of the testes was discovered to be the most simple but reliable method for managing reproduction and sexual behavior in the male. Today, there continues to be global utilization of castration in domestic animals. More than six hundred million pigs are castrated every year, and surgical removal of testes in dogs and cats is a routine practice in veterinary medicine. However, modern biological research has extended the meaning of sterilization to include methods that spare testis removal and involve a variety of options, from chemical castration and immunocastration to various methods of vasectomy. This review begins with the history of sterilization, showing a direct link between its practice in man and animals. Then, it traces the evolution of concepts for inducing sterility, where research has overlapped with basic studies of reproductive hormones and the discovery of testicular toxicants, some of which serve as sterilizing agents in rodent pests. Finally, the most recent efforts to use the immune system and gene editing to block hormonal stimulation of testis function are discussed. As we respond to the crisis of animal overpopulation and strive for better animal welfare, these novel methods provide optimism for replacing surgical castration in some species.

Evaluation of chemical castration using intra-testicular injection of zinc gluconate into the testis of the male donkey versus surgical castration: antimullerian hormone as an endpoint marker

BACKGROUND

Chemical castration of male animals is an alternative to surgical castration for inducing azoospermia, consequent sterility. Intra-testicular injection of zinc gluconate has been used for chemical castration in several animal species. However, its application to equine species, such as donkeys, has yet to be reported. This study aimed to evaluate the use of zinc gluconate for the chemical castration of male donkeys and to compare its effectiveness relative to routine surgical castration. For this purpose, investigations of serum testosterone and anti-Müllerian hormone levels, testicular ultrasonographic echogenicity, and histopathological findings were performed.

METHODS

Fourteen clinically healthy adult male donkeys were randomly and equally divided into two groups. The donkeys in group I (n = 7) underwent surgical castration. The donkeys in group II (n = 7) received intra-testicular zinc gluconate injections. The donkeys were kept under close clinical observation for 60 days. Abnormalities in donkey behavior and gross alterations in the external genitalia were recorded daily. Serum testosterone and anti-Müllerian hormone (AMH) levels were measured 15 days before the start of the treatment and 15, 30, 45, and 60 days after treatment. The testicles of group II donkeys were evaluated ultrasonographically. At the end of the study, the testes were removed and histologically examined.

RESULTS

Serum testosterone levels significantly declined compared to pre-castration levels in surgically castrated donkeys (group I), but donkeys exposed to chemical castration (group II) showed a non-significant reduction in testosterone levels. Donkeys in the surgical group had considerably lower serum AMH levels. In contrast, there was a non-significant (p > 0.05) increase in AMH levels in the chemical group compared with the pre-sterilization level. In addition, ultrasonographic examination revealed that the testicular echo-density had changed, as observed by a few scattered hyperechoic regions throughout the entire testis parenchyma. The histopathological investigation confirmed the presence of necrosis of the spermatogenic epithelium, increased thickness of the basement membrane of the seminiferous tubules, marked interstitial fibrosis, and shrinkage of the seminiferous tubules. Furthermore, syncytial giant cells were present in the lumen of seminiferous tubules and were associated with Sertoli cell vacuolation. Donkeys subjected to chemical castration (group II) had orchitis, as confirmed histopathologically.

CONCLUSION

Intra-testicular injection of zinc gluconate resulted in histopathological and ultrasonographic testicular changes in adult male donkeys, which may affect their reproductive potential. However, it did not significantly alter serum testosterone or AMH levels, indicating that it cannot be used as a substitute for surgical castration in male donkeys.

Investigating the influence of neuter status on paw preference in dogs and cats

Motor lateralization is commonly observed through preferential paw use in dogs and cats. Previous studies have uncovered sex-related differences in paw preference, hypothesizing that these differences may be related to sex hormones. The current study aimed to compare neutered and entire individuals to further investigate whether paw preference is influenced by sex hormones. Dog and cat owners were required to fill in a questionnaire with demographic information such as sex and neuter status of their pets. They then carried out two simple paw preference tasks within their homes: a "reaching for food" task and a "reaching for a toy" task. This study revealed an overall preference among the 272 dogs and 137 cats tested to use their right paw in both tasks. In cats, the degree of paw preference (i.e., regardless of the direction) was significantly influenced by an interaction between neuter status and life stage. Also in dogs, both life stage and an interaction between neuter status and life stage tended to influence the degree of paw preference. Post-hoc power analysis revealed a lack of statistical power, suggesting that future studies using a larger sample size are needed to further investigate potential effects of neuter status on paw preference.

New Prospects in Neutering Male Animals Using Magnetic Nanoparticle Hyperthermia

Controlling populations of free-roaming dogs and cats poses a huge challenge worldwide. Non-surgical neutering strategies for male animals have been long pursued, but the implementation of the procedures developed has remained limited to date. As submitting the testes to high temperatures impairs spermatogenesis, the present study investigated localized application of magnetic nanoparticle hyperthermia (MNH) to the testicles as a potential non-surgical sterilization method for animals. An intratesticular injection of a magnetic fluid composed of manganese-ferrite nanoparticles functionalized with citrate was administered followed by testicle exposure to an alternate magnetic field to generate localized heat. Testicular MNH was highly effective, causing progressive seminiferous tubule degeneration followed by substitution of the parenchyma with stromal tissue and gonadal atrophy, suggesting an irreversible process with few side effects to general animal health.

Chemical sterilization with intratesticular administration of zinc gluconate in adult dogs: a preliminary report

BACKGROUND

Chemical sterilization with zinc gluconate is being developed due to its permanent contraceptive effect in prepubertal dogs. In this study, five healthy adult dogs were selected randomly. Semen samples were collected and analyzed before the study to confirm normal testicular function. Under general anesthesia, pH neutralized zinc gluconate was injected directly into their testes. Testes diameter, ultrasonographic appearance, changes in the percentage of white blood cells, and testosterone concentration were monitored twice a week before and 1 month after the injection. At the end of the study, the dogs were castrated and their testes were removed for histopathological evaluation.

RESULTS

The general health of all dogs was normal after the injection. The appearance of testicular swelling was limited within 2 days of treatment. The average diameter of left and right testes was 2.48 and 2.03 cm before the injection and reached to diameter 2.12 and 2.15 cm, respectively, at the end of the study. Serum testosterone concentration was 4.2 ng/ml at the start and 4 ng/ml at the end of the study. The percentage of white blood cells at the start and end of the study were within normal ranges reported for dogs. Histopathological analyses indicate a degeneration of germ cells in seminiferous tubules, but Leydig cells retained their structure.

CONCLUSIONS

Therefore, It is inferred that the injection of pH neutralized zinc gluconate into the adult dogs' testes resulted in the loss of sperm-producing tissue without affecting the production of testosterone and the general health of adult dogs.

Effects of chemical castration using 20% CaCl2 with 0.5% DMSO in tomcats: Evaluation of inflammatory reaction by infrared thermography and effectiveness of treatment

This study used infrared thermography to monitor the immediate inflammatory reaction to an intratesticular injection of 20% (calcium chloride) CaCl₂ with 0.5% dimethyl sulfoxide (DMSO) for chemical castration and to provide evidence of the treatment's clinical viability. Six animals received a 0.25 mL intratesticular injection of 20% CaCl₂ with 0.5% DMSO in each testis. Thermographic imaging, testicular measurement, penile spine evaluation, electroejaculation, and sperm analysis were performed before the injection. Eighty days post-injection, the cats were evaluated again, then received an orchiectomy followed by histological analysis. Infrared thermography of the testicular area was performed before (M0) and after anesthesia (M0A); after electroejaculation (M0E); 10 min (M1), 1 h, (M2) and 6 h (M3) after the injection for seven consecutive days (M4-10); after 15 (M11) and 30 days (M12); and after 80 days, before and after anesthesia and after electroejaculation (M13, M13A and M13E). No cats had a significant increase in testicular temperature or behavioral changes. All animals were azoospermic and had a 50% reduction in total testicular volume after 80 days. Histologically, the testes showed different degrees of degeneration, necrosis, calcification and replaced connective tissue, as well as Leydig cell hyperplasia in 7/12 of the testes. Infrared thermography efficiently diagnosed and monitored scrotal inflammation caused by intratesticular injection of 20% CaCl₂ solution with 0.5% DMSO, and it is suggested that a single injection of this compound can cause azoospermia after 80 days. We concluded by infrared thermography with a clinical exam, that the adverse reactions were minimal and did not interfere with animal welfare.

Nanocarrier-mediated delivery of α-mangostin for non-surgical castration of male animals

The overpopulation of abandoned and stray companion animals has become a global crisis. The main purpose of this study was to develop a novel nanomedicine-based antifertility compound for non-surgical castration of male animals. Mangosteen (Garcinia mangostana L) pericarp extract has been shown to exhibit anti-fertility property. α-mangostin (AM)-loaded nanostructured lipid carrier (AM-NLC) was developed to improve male germ cell apoptosis. This study was conducted to investigate physicochemical properties of AM-NLC and determine the biological effects of AM-NLC on spermatogonia cells and testicular explants obtained from castrated testes. AM-NLC was produced through a hot homogenization technique. The negatively charged particle of AM-NLC was nano-sized with a narrow dispersity. AM-NLC exhibited antiproliferative activity towards spermatogonium cells. It induced apoptosis in the cells. In addition, AM-NLC exhibited anti-inflammatory activities in lipopolysaccharide-activated macrophages. Abnormal anatomy of seminiferous tubule was noted following treatment of testicular explant with AM-NLC. This nanomedicine-based sterilant would be a promising platform that may have utility in non-surgical castration of male animals by intra-testicular injection.

Owned dog ecology and demography in Villa de Tezontepec, Hidalgo, Mexico

Dog overpopulation in developing countries has negative implications for the health and safety of people, including the transmission of zoonotic diseases, physical attacks and intimidation to humans and animals, as well as impacts on canine welfare. Understanding the ecology and demographic characteristics of a dog population can help in the planning and monitoring of canine population control programs. Little data exist regarding demography and dynamics of domestic dog populations in semi-urban areas in Mexico. A cross-sectional study was carried out between October 21 and November 7, 2015, to characterize the dog ecology and demography in Villa de Tezontepec, Hidalgo, Mexico. A face-to-face survey was used to collect data from randomly selected households in four contiguous communities using stratified two-stage cluster sampling. Within each household, adults answered questions related to their dogs and their experiences with dog bites and aggression. A total of 328 households were interviewed, representing a participation rate of 90.9% (328/361) and 1,450 people. Approximately 65.2% of the households owned one or more dogs, with a mean of 1.3 (SD=1.5) and 2.0 (SD=1.5) owned dogs in all participant households and dog-owning households, respectively. The human: owned dog ratio for all participant households was 3.4:1 (1450/428), and for the dog-owning households was 2.3:1 (984/428). The owned dog male: female ratio was 1.4:1 (249/179). Approximately 74.4% (95.0% CI=69.8% - 78.7%) of the owned dogs were older than one year (mean age: 2.9 years; SD=2.5). The mean age of owned female dogs at first litter was 1.9 years (SD=1.2) and the mean litter size was 4.2 puppies (SD=2.1). Approximately 36.9% (95.0% CI=31.8% - 46.4%) of the females were spayed, and 14.1% (95.0% CI=10.7% - 19.7%) of the males were neutered. Only 44.9% (95.0% CI=40.1% - 49.7%) were always confined when unsupervised. Approximately 84.4% (95.0% CI=80.6% - 87.7%) were reported to have been vaccinated against rabies in 2015. The knowledge of owned dog demography and ecology provided by this study can inform local government planning of dog population control interventions, and could serve as a baseline for the development of agent-based models to evaluate the effects of different dog population control strategies on dog demography.

Effects of surgical and chemical sterilization on the behavior of free-roaming male dogs in Puerto Natales, Chile

Population management of free-roaming domestic dogs (Canis lupus familiaris) is of interest due to the threat these animals pose to people, other animals and the environment. Current sterilization procedures for male dogs include surgical and chemical methods. However, little is known about how these procedures affect their behavior. The primary objective of this study was to investigate changes in selected behaviors following chemical and surgical sterilization in a male free-roaming dog (FRD) population in southern Chile. We also examined the association between serum testosterone levels and behaviors thought to be influenced by circulating androgens. A total of 174 dogs were randomly assigned to either a surgical or chemical sterilization group, or a control group. At the onset of the intervention period, 119 dogs remained and 102 dogs successfully completed the study. Each dog was monitored pre- and post-intervention using video recordings, GPS collars, and blood samples for the measurement of testosterone. Analysis of behavior revealed that surgically castrated dogs showed no reduction of sexual activity or aggression when compared to their pre-intervention behavior. Chemically sterilized dogs showed a statistically significant increase in dog-directed aggression, but no change in sexual activity. There was no change in home range size in any groups between the pre- and post-intervention measurement. We found no consistent association between levels of serum testosterone concentration and behavioral changes in any of the groups. This study presents the first detailed behavioral observations following surgical and chemical sterilization in male FRDs. The information generated is highly relevant to communities struggling with the control of FRDs. Complementary studies to further our understanding of the effects of male sterilization on the behavioral and reproductive dynamics of FRD populations are needed.

Intratesticular and intraepididymal injections to sterilize male cats: From calcium chloride to zinc gluconate and beyond

AIM AND RATIONALE

The aim of intratesticular and intraepididymal injections is to provide an inexpensive non-surgical method for sterilizing tom cats. Intratesticular and intraepididymal injections have been studied for decades and warrant continued investigation. While both methods result in azoospermia, intratesticular injection of sclerosing agents induces orchitis, resulting in decreased spermatogenesis, whereas intraepididymal injection blocks sperm transport but does not alter spermatogenesis.

EVIDENCE BASE

Sclerosing agents that have been used effectively for intratesticular injections in cats include calcium chloride dihydrate and zinc gluconate. For sclerosis by intraepididymal injections, chlorhexidine digluconate has been used successfully in cats. The volume, formulation and concentration of sclerosing agents for intratesticular and intraepididymal injections in cats have not been standardized.

CHALLENGES

Neither intratesticular nor intraepididymal injections entirely eliminate gonadal testosterone production, which may be undesirable for pet cats and therefore may restrict the application of this method of sterilization to feral cats with limited human contact. In addition, both methods may require sedation or general anesthesia, leading some to support routine castration over these non-surgical methods. Lastly, even if the technique is successful in inducing permanent sterility, normal fertility may persist in treated males for 1-2 months after treatment because of sperm present within the epididymis and vas deferens.

Changes in blood testosterone concentrations after surgical and chemical sterilization of male free-roaming dogs in southern Chile

There is a growing interest in chemical sterilization as an alternative to surgical castration in large-scale sterilization campaigns to control canine populations. An important step toward understanding the short-term and long-term effects of chemical sterilants is to determine their impact on blood testosterone concentrations, particularly as these could influence dog behavior after treatment. A field trial was conducted with 118 free-roaming male dogs in the Chilean Patagonia, where 36 dogs were chemically sterilized using EsterilSol, 39 dogs were surgically castrated, and 43 dogs remained intact as controls. Blood testosterone levels were determined at four time periods: on enrollment 6 months before treatment (t-6m), at the time of treatment (t0, within one hour after surgical castration or chemical sterilization and during a concurrent 2-week period for the control group), four (t+4m), and six (t+6m) months after treatment. Intrinsic and temporal factors were evaluated; age was significantly associated with testosterone, where dogs 2- to 4-year-old had the highest testosterone concentrations (P = 0.036), whereas body weight and body condition scores were not associated with testosterone; testosterone concentration was not influenced by time of day, month, or season. After treatment (t+4m and t+6m), all of the surgically castrated dogs had testosterone concentrations below 1.0 ng/mL. On the basis of this cut point (<1 ng/mL), testosterone remained unchanged in 66% of the chemically sterilized dogs at both t+4m and t+6m; it remained low for 22% of dogs at both t+4m and t+6m; it was unchanged at t+4m but low at t+6m in 9% of dogs; and, it was low at t+4m but reverted back to unchanged at t+6m in one dog (3%). Incidentally, testosterone in chemically sterilized dogs increased dramatically within 1 hour of treatment (t0), more than doubling (131%) the concentration of control dogs at the time of treatment (t0), likely because of severe necrosis of interstitial cells. The use of EsterilSol as a method of sterilizing dogs had a variable effect on blood testosterone concentrations. Approximately, 30% of chemically sterilized dogs had a reduced testosterone concentration (actual maximum, 1 ng/mL) after 6 months, similar to that of surgically castrated dogs. Most chemically sterilized dogs, however, showed no long-term changes in blood testosterone concentrations.

A dose-finding, long-term study on the use of calcium chloride in saline solution as a method of nonsurgical sterilization in dogs: evaluation of the most effective concentration with the lowest risk

Background

Canine overpopulation is a global issue with serious health and welfare implications. Nonsurgical methods of sterilization could yield positive impacts on this problem, but no long-term data on such methods are available. The objective of the current investigation was to determine the effects of intratesticular injections of calcium chloride dihydrate (CaCl₂) in saline in dogs over a one year period. Five concentrations (0%, 10%, 20%, 30%, 60%) of CaCl₂ in saline were administered via intratesticular injection to groups of 10 dogs each. Total sperm count and motility, blood levels of testosterone, and side effects were examined at 0, 2, 6, and 12 months post-injection (PI). Testicular size and semen volume were examined at 0 and 12 months PI.

Results

Total sperm count, semen volume and testosterone showed significant dose-dependent decreases upon treatment with 10%-60% CaCl₂ compared with either the control group (0% CaCl₂) or baseline for each treatment group. Azoospermia was achieved for at least 12 months PI in 60% and 80% of treated dogs after administration of a 10% and 20% CaCl₂, respectively. Treatment with 30% or 60% CaCl₂ resulted in azoospermia in 100% of dogs, but more side effects were observed, while no side effects were noticed at lower doses. For each treatment group, testosterone levels had decreased an average of 35%-70% at 6 months following treatment. However, testosterone levels rebounded by the 12-month time point in all groups except the highest dosage group (60% CaCl₂), which remained at the low end of physiological range throughout the study. Sperm motility dropped to zero or near zero in all dogs treated with CaCl₂. Testicular size was significantly smaller at 12 months PI for all groups when compared to baseline.

Conclusions

This first long-term study confirms reports of the efficacy of CaCl₂ sterilization. However, at dosages free of adverse events, calcium chloride in saline may not provide permanent sterilization as previously believed. Future work should explore optimized solvents to increase the permanence of the well-tolerated 20% formulation.

Induction of contraception by intraepididymal sclerotherapy

PURPOSE

The objective of the present study was to evaluate the efficacy of a sclerosing solution for inducing epididymal occlusion in male rats.

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into two groups: an injection group (n=20) and control group (n=20). Before injecting the sclerosing agent, seminal vesiculectomy and sperm identification using electrostimulation were performed in all of the rats. In the injection group, 0.2 mL of 0.1% sodium tetradecyl sulfate solution was injected into the epididymis. In the sham group, only the identification of the epididymis was performed. At 4 and 12 weeks after the injection, semen was collected by electrostimulation and evaluated to assess the contraceptive effect. Epididymis was evaluated by hematoxylin and eosin (H&E) staining.

RESULTS

After 4 and 12 weeks, semen collection was performed in the two groups. Sperms were not observed in the injection group, while there was no change in the sperms in the sham group. H&E staining showed the obstruction of epididymal tubules and an accumulation of inflammatory cells in the injection group.

CONCLUSIONS

This study showed that the sclerosing agent induced sterilization in male rats. This result suggests that the injection method can replace vasectomy as a contraceptive method. However, a further study of large animals and a clinical study are needed. Further, the long-term effectiveness of this method needs to be studied.

Intratesticular injection of hypertonic saline : non-invasive alternative method for animal castration model

Previous studies, including our own, have demonstrated that the intratesticular injection of hypertonic saline (20%) decreased serum testosterone level which was similar to the surgical castration in the rat, showing the state of chemical castration. In the present study, we further verify the efficacy of this less invasive method as an alternative of surgical orchidectomy in the andevrepological field. Sterilized 20% saline was directly injected into the adult male rats (750 μl per testis). The tested rats were divided into 3 groups including intact group (intact), orchidectomy group (ORX) and saline injection group (SAL) after bilateral orchidectomy was performed at the same day of injection. All rats were sacrificed at 4 weeks after injection. The reproductive organs (testes, epididymis, seminal vesicles and prostates) were collected and used for DNA and protein pattern analyses. Also, patho-histological studies on the testes were performed. In contrast to the intact group, similar DNA damages of testis and seminal vesicle were appeared in ORX group and SAL group. The DNA degradations seemed to be the results of necrosis rather than apoptosis. In the protein pattern analysis, all the testing tissues exerted similar patterns in the ORX group and the SAL group compared to the those of intact group. Patho-histological studies revealed that severe degenerative changes in testicular seminiferous tubules and massive infiltration of immune cells in SAL group. The present study confirmed that direct injection of hypertonic saline into the testis caused the equivalent biochemical changes in the accessory sex organs as shown in the orchidectomized animals. These results suggest that hypertonic saline injection model could be a useful castration model which can substitute for surgical castration when its safety is secured through further study in the future.

Current and future tools for global canine rabies elimination

Even though rabies is almost uniformly fatal, it is readily preventable with currently available tools. Vaccination is highly efficacious for the pre-exposure prophylaxis (PrEP) of rabies in humans and animals, and prompt postexposure prophylaxis (PEP) with vaccine and rabies immune globulin (RIG) can reliably prevent disease in humans. However, access to these tools and knowledge of their proper use are often limited, especially in impoverished, rabies-enzootic countries with the highest disease burden. In the absence of reliable diagnostic capacity and risk assessments, vaccines and RIG are often administered inappropriately, leading to chronic supply shortages and otherwise preventable deaths. Rather than focusing solely on human prophylaxis, it is more cost-effective over the long term to eliminate canine rabies in its natural terrestrial reservoirs. Because more than 99% of human rabies deaths result from dog bites, prevention efforts should focus on dogs. A versatile "One Health" strategy for canine rabies elimination should aim to create sustainable herd immunity in dogs, using proven vaccination strategies at the local level, coupled with community education and humane population management. Such strategies have succeeded in both developed and developing countries, and can be adapted to any locality. Numerous examples in Africa, Asia, and Latin America have shown that community-based, locally guided vaccination and education programs, based on a shared vision and long-term commitment, can eliminate canine rabies. Such programs should have specific goals and measurable outcomes, and should be conducted under the guidance of supportive governments, in collaboration with international partners and nongovernmental organizations. In addition to currently available tools, rabies prevention can be augmented by new dose-sparing human vaccine schedules, alternative routes of vaccine administration, monoclonal antibodies as an alternative to RIG, sensitive and specific point-of-care diagnostics and the development of canine immunocontraceptive methods. Accurate risk assessments of potential human exposures and support for decentralized laboratory capacity will be essential to ensure the most effective utilization of vaccines and RIG until canine rabies has been eliminated.