Histological and Morphometric Examination of the Testes of Boars and Male Pigs Immunocastrated with Improvac®

Abstract

Background: Surgical castration of male piglets is frequently performed to prevent development of an unpleasant taste and flavor in meat of mature males, called boar taint. Disadvantages of this method are primarily related to the lower feed efficiency of surgically castrated male pigs, production of less lean meat and more fat on the carcasses than boars, as well as ethical issues associated with the procedure itself. Immunocastration is a method of immunization against gonadotropinreleasing hormone (GnRH) and represents an alternative to avoid boar taint. This study aimed to examine the influence of immunocastration on histological and morphometric parameters of male pig testes.Materials, Methods & Results: A total of 60 crossbred male pigs selected from 30 litters were assigned to two experimental groups: boars (n = 30) and immunocastrated males (n = 30). Two doses (2 mL per dose) of the Improvac® vaccine were given to pigs scheduled for immunocastration. The first injection was given at 10 weeks of age, and the second injection at 20 weeks of age. All pigs were fed the same commercial diet ad libitum, group-housed (15 pigs/pen) and slaughtered at 25 weeks of age. After slaughter, testicle weights were measured and samples of testicular tissue were taken for histological examination. Immunocastrated males had lower testicle weights than boars (P < 0.01). Furthermore, structural damage to the germinal epithelium was visible in the seminiferous tubules of vaccinated pigs. In the testicular interstitium of these animals, the number of Leydig cells were reduced; almost all of these cells exhibited different degrees of abnormality. Moreover, the diameter of the seminiferous tubules and thickness of the germinal epithelium were greater (P < 0.01), and the percentage of germinal epithelium in the seminiferous tubules as well as percentage of blood vessels in the interstitium were higher in boars as compared to immunocastrated males (P < 0.01). Seminiferous tubule lumen diameter was greater (P < 0.01), and percentage of lumen in the seminiferous tubules as well as percentage of non-blood vessel tissue in the interstitium were higher in immunocastrated males than boars (P < 0.01).Discussion: Vaccination against GnRH, as used in this study, reduced the synthesis of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which led to decreased spermatogenesis and androgen production. The smaller diameter of the seminiferous tubules as well as germinal epithelium thickness, and lower percentage of germinal epithelium in the seminiferous tubules in immunocastrated males could be explained by reduced FSH synthesis, and subsequent reduced spermatogenesis. The described testicular malformations in immunocastrated animals caused their lower weight, and greater diameter of the lumen as well as a higher lumen percentage of the seminiferous tubules. The vaccine reduced LH synthesis, so the Leydig cells of immunocastrated animals had lower activity than the same cells in boars. The percentage of blood vessels in the interstitium of boar testes was higher, which was related to the blood supply required for normal function of Leydig cells. It was concluded that differences existed in the structure of the seminiferous tubules and interstitium between boars and immunocastrated males , which were reflected in values of the examined histological and morphometric parameters. The development of these differences was related to the inhibition of GnRH synthesis and secretion.

Leydig Cells in Immunocastrated Polish Landrace Pig Testis: Differentiation Status and Steroid Enzyme Expression Status

“…The injection of the vaccine is a systemic event that disturbs the hormonal homeostasis of the animal thus adverse effects could be expected in other tissues apart from the testes. A previous study has suggested that immunization against GnRH damages the hypothalamus [ 45 ]. In addition, findings from boars immunocastrated with GnRH antagonist, deslorelin, Polish Landrace × (Duroc × Pietrain) showed morphological and functional alterations in the testes and epididymis, although with a significant increase in spermatozoa production [ 46 , 47 ].…”

“…PDFGFα signaling is a regulator of many developmental processes, including the formation of the male gonad [ 45 ]. PDGFRα is the only known marker of ALC stem cells that can self-renew and give rise to ALCs both in vivo and in vitro [ 51 ].…”

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

“…In addition, the timing of the two doses relative to slaughter is particularly important, as reproductive function tends to recover over time. While disrupted testis morphometry and spermatogenesis are reported in GnRH-immunized pigs at slaughter age (~6 months old) ( 497 , 508 , 509 ), boars treated with two doses of Improvest® at 10 and 15 weeks of age recovered testosterone levels by 40 weeks of age and sperm concentration and motility by 60 weeks ( 509 ). Because hogs are usually sent to market by 24–26 weeks of age, before the testis can recover, the immunization procedure is considered equivalent to castration.…”

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

“…Puberty is a period characterized by rapid reproductive development and may be perceived by the increase in testicular growth. On the other hand, the effectiveness of immunocastration can be predicted indirectly through testicular measurements [24][25][26] or the development of sexual accessory glands [27], as immunocastrated animals have less developed genital organs [28]. The morphometric analysis of scrotal gonads, considering pre-and post-pubertal values, can then be a useful tool when evaluating the effectiveness of immunocastration protocols.…”