Immunological castration temporarily reduces testis size and function without long-term effects on libido and sperm quality in boars

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.

The effect of timing of Improvest administration on growth performance and carcass characteristics in gilts

Improvest (IMP; Zoetis Inc., Parsippany, NJ) has been approved by the U.S. Food and Drug Administration for use in gilts. Improvest is administered twice: the first dose should be administered no earlier than 9 wk of age and the second dose (D2) at least 4 wk after the first dose. The aim of this study was to determine how the timing of IMP before harvest affects growth performance and carcass characteristics in gilts. A total of 1,632 gilts were allocated to four groups (12 pens/treatment; 34 gilts/pen): 1) a control group did not receive IMP; 2) T-early gilts received IMP on day 7 (day 0 = 10 wk postweaning), and D2 on day 40 (i.e., 35 d prior to first removal for harvest); 3) T-medium gilts received IMP on day 21 and D2 on day 56 (i.e., 19 d prior to first removal for harvest); 4) T-late gilts received IMP on day 35 and D2 on day 70 (i.e., 5 d before first removal for harvest). Pigs were selected for harvest by visual observation on days 75, 89, 103, and 117: 1) the heaviest 7 gilts/pen for each treatment on day 75; 2) the heaviest 10 gilts/pen of each treatment at day 89; 3) the heaviest 10 gilts/pen of each treatment on day 103; and 4) the remaining 7 gilts/pen on day 117. Weights and feed disappearance were recorded every 2 wk and during harvest dates to calculate average daily gain (ADG), average daily feed intake (ADFI), and feed efficiency (Gain:Feed; G:F). Generalized linear mixed models of SAS were used to analyze all variables. The increase in ADFI over Control gilts was observed 15 d post D2 and continued through 77 d post D2, with advantages in ADG occurring between 15 and 35 d post D2. Control and IMP treated gilts had similar G:F 15 to 33 d post D2. The overall ADG and ADFI from day 0 to market, final live weights, and hot carcass weights were significantly greater (P ≤ 0.05) in IMP gilts compared to Control. When G:F based on live weight was averaged across all groups (i.e., from day 0 to market), T-early had the lowest (P ≤ 0.05) G:F compared to Control, T-medium, and T-late gilts, which did not differ. Carcasses from IMP gilts had increased (P < 0.01) backfat, but similar (P = 0.5) Longissimus muscle depth, compared to Control. Within a cohort of similar aged gilts finishing during the summer, this study indicates that the trajectory of growth is enhanced within a similar window post D2 of IMP. Gilts treated with IMP had heavier carcasses with increased backfat and similar Longissimus muscle depth.

Immunocastration in adult boars as a model for late-onset hypogonadism

Background

While immunocastration has been studied in male pre‐pubertal pigs, data on older, sexually mature animals are limited. To understand the physiological effects of androgen deprivation in the late sexual development phase, we compared mature immunocastrated boars (n = 19; average age = 480 days) to young male immunocastrated pigs (n = 6; average age = 183 days) and young entire males (n = 6; average age = 186 days) as positive and negative controls, respectively.

Objectives

We hypothesized that the timing of gonadotropin‐releasing hormone suppression (early or late sexual development phases) influences the extent of reproductive function inhibition, histological structure of testicular tissue, and expression levels of selected genes related to steroid metabolism.

Materials and methods

Antibody titer, hormonal status, and histomorphometric analysis of testicular tissue were subjected to principal component analysis followed by hierarchical clustering to evaluate the immunocastration effectiveness in mature boars.

Results

Hierarchical clustering differentiated mature immunocastrated boars clustered with young immunocastrated pigs from those clustered with entire males. Although all mature immunocastrated boars responded to vaccination, as evidenced by the increased gonadotropin‐releasing hormone antibody titers (p < 0.001), decreased serum luteinizing hormone concentrations (p = 0.002), and changes in testicular tissue vascularization (lighter and less red testicular parenchyma; p ≤ 0.001), the responses were variable. Sharp decreases in testes index (p < 0.001), Leydig cell volume density (p < 0.001), Leydig cell nucleus‐to‐cytoplasm ratio (p < 0.001), and testosterone concentration (p < 0.001) were observed in mature immunocastrated boars clustered with young immunocastrated pigs compared with those that clustered with entire males. Additionally, mature immunocastrated boars clustered with young immunocastrated pigs showed lower hydroxysteroid 17‐beta dehydrogenase 7 expression than entire males (p < 0.05). The young immunocastrated pigs group showed higher follicle‐stimulating hormone receptors than the entire males and mature immunocastrated boars, lower steroidogenic acute regulatory protein expression levels compared with entire males, and mature immunocastrated boars clustered with entire males (p < 0.01).

Conclusion

The two‐dose vaccination regime resulted in progressive but variable regression of testicular function in adult (post‐pubertal) pigs; however, it was insufficient to induce a complete immunocastration response in all animals.

Long-Term Immunocastration Protocols Successfully Reduce Testicles' Size in Bísaro Pigs

Simple Summary

Surgical castration is an ongoing problem in pig production, especially in breeds reared until older ages, like the Bísaro pig. To avoid this technique, three immunocastration protocols with different numbers of injections and times of inoculation were tested. Scrotal measurements were used to attest their effectiveness. The best protocol was the one with three administrations starting at three months old. It was able to maintain the testis size below puberty size for 16 weeks following the last injection.

Abstract

This study aimed to find a suitable immunocastration protocol for male Bísaro pigs (BP) due to the breed and production system particularities. Twenty-five male BP were treated with Improvac^® according to three protocols: using two (GrpE2 and L2) or three vaccinations (GrpL3) and starting at 9 (GrpE2) or 13 weeks old (GrpL2 and L3). Eleven animals were kept as intact males (GrpC). Scrotal measurements and the morphometry of the testes and epididymides collected at slaughter were used to survey the effectiveness of the immunocastration compared with the age-matched intact controls. Animals in groups E2 and L3 were kept until 57 weeks, after a second vaccination cycle at 49 and 53 weeks of age. Scrotal dimensions decreased to almost initial values in treated animals until 17 (GrpE2) and 21 weeks (GrpL2 and L3), thereafter increasing to post-pubertal values until around 29 or 37 weeks of age for groups E2 and L2, respectively, but only at 41 weeks in group L3. Between 41 and 49 weeks, scrotal dimensions were similar in treated and control animals, decreasing to the predicted pre-puberty size after the second cycle of vaccination. This study suggests the most suited protocol for males slaughtered at older ages includes three administrations of Improvac^® starting at 3 months of age, followed by a second vaccination cycle.

Effect of immunological castration of male pigs on morphological and functional con-dition of the testicles

Changes in the priorities of the treatment of animals in the conditions of intense technology of production of livestock products are based on the necessity of wellbeing of animals. Therefore, there is a need of search for and broad introduction of generally accepted alternatives to surgery, which would use modern means of castration, particularly immunocastration. The study presents morpho-functional substantiation of practicability of using immunological castration in the conditions of industrial production of pork. At the same time, we studied immunological castration using Improvak on the morphological and physiological condition of the testicles of male pigs. The testosterone level was determined using radioimmunologic method after 2, 4, 6, 8 weeks of immunological and surgical castrations, and also in intact boars of the control group. During the slaughter, we selected biopates of the testicles in immunological castrates and pigs of the control group for histological examination. The testosterone level 2 weeks after castration was the lowest in the animals castrated using Improvak. This indicator gradually increased, and after 8 weeks was higher than in the surgically castrated pigs. In the latter, the level of testosterone gradually decreased for 8 weeks, and did not significantly change in non-castrated pigs. The last stages of spermatogenesis in immunocastrates were inhibited after the second vaccination. As a result of immunological castration, the interstitial tissue of the testicle underwent changes. Between the tubules, a spreading of the loose connective tissue was observed. Leydig cells lost hyper chromaticity of the cytoplasm and typical polygonal profile, and their functional potential decreased. This fact was confirmed by the changes in the Hertwig’s ratio. In particular, we observed decrease in the value of the nuclear-cytoplasmic ratio. There were also a time shift of mitotic cycle, low degree of differentiation of spermatogonia and rupture of the course of the subsequent stages of spermatogenesis. However, there occurred multiplication of primary spermatogonia, single cellular divisions, and in the ductus deferentes, there could be found single spermatids. Some of them formed specific cellular groups of rounded and elliptic shapes in the seminiferous tubules. These structures were absent in the testicles of the control animals. Microstructural changes in the swine after injecting Improvak were characterized by deficiency of Leydig cells, indicating absence of the normal hormonal background, as confirmed by the results of the study of testosterone level. The epithelium-spermatogenic layer was underdeveloped, and the lumens of the tubules were in some places filled with generations of spermatocytes. In some places, meiosis was observed, which also indicates insignificant functioning of the testicles. Vaccination with Improvak caused atrophy of the testicles in swine and decrease in their functional condition, allowing it to be recommended it for broader application as an alternative to surgical castration.

Immuno-castration of female and male pigs with anti-gonadotrophin releasing hormone vaccine: Morphometric, histopathological and functional studies of the reproductive system

Immuno-castration is increasingly recommended in pigs due to welfare reasons; however, there are few studies in females compared to males. This aim of this study was to investigate the effects of immuno-castration in female and male pigs. The weight, the morphometric and microscopic characteristics of the reproductive organs, and the hormone concentrations were studied in 12 immunocastrated females (IF) and 12 immunocastrated males (IM) and compared with control animals (C). At slaughter, IF tended to have greater body weights than CF (P =  0.051), whereas in IM and CM pigs there were not body weight differences (P =  0.140). The weight of the reproductive tract and size of all individual organs were less in IF compared with CF. Results from histological assessments indicated IF had more atretic follicles and a thinner endometrial mucosa than control females. Hormone concentrations were not different between CF and IF (P >  0.050). As a result of immuno-castration, there was impaired spermatogenesis in most males. Results from microscopic evaluations indicated there was a marked decrease of spermatogonial cells and size of Leydig cells in the testicles. Accessory gland structures were affected in CM and IM with there being differences in gross and microscopic characteristics. Testosterone concentrations, unlike estradiol, were different in IM compared to CM (P <  0.001). These results provide evidence that immuno-castration with the anti-gonadotrophin releasing hormone vaccine is effective in female and male pigs and induces morphological and endocrine changes incompatible with fertility.

Reversibility and safety of KISS1 metastasis suppressor gene vaccine in immunocastration of ram lambs

Objective

The aim of this study was to investigate the reversibility and safety of KISS1 metastasis suppressor (KISS1) gene vaccine in immunocastration.

Methods

Six eight-week old ram lambs were randomly divided into vaccinated and control groups. The vaccine (1 mg/ram lamb) was injected at weeks 0, 3, and 6 of the study. Blood samples were collected from the jugular vein before primary immunization and at weeks 2, 4, 6, 10, 14, 22, and 30 after primary immunization. All ram lambs were slaughtered at 38 weeks of age, and samples were collected.

Results

The specific anti-KISS1 antibody titers in vaccinated animals were significantly higher and the serum testosterone level was significantly lower than those in the control groups from week 4 to 14 after primary immunization (p<0.05). No significant difference was observed at weeks 22 and 30 after the primary immunization. Similar results were also found for scrotal circumference, testicular weight, length, breadth, and spermatogenesis in seminiferous tubules in week 30 after primary immunization. KS (KISS1-hepatitis B surface antigen S) fusion fragment of KISS1 gene vaccine was not detected in host cell genomic DNA of 9 tissues of the vaccinated ram lambs by polymerase chain reaction.

Conclusion

The effects of KISS1 gene vaccine in immunocastration were reversible and no integration events were recorded.