Abstract
The objective of this study was to evaluate the testicular biometric, seminal, and plasma testosterone levels in lambs subjected to an anti-GnRH vaccine as a method of castration. Thirty entire, crossbred Santa Inês male lambs were randomly distributed into three treatment (T): T1 was the control group, with the administration of 1 mL of saline solution subcutaneously (SC); 1.0 and 0.5 mL of an anti-GnRH vaccine were administered SC in T2 and T3, respectively. Testicular biometric variables, physical and morphological variables of semen, and plasma testosterone concentrations were evaluated. At D60, there was a reduction in testicular length, width, thickness, and scrotal circumference of the immunocastrated animals regardless of the vaccine dose used (P < 0.05). A reduction in semen physical variables at both dosages (P < 0.05) was observed, with azoospermia, in 80% and 70% of animals in the T2 and T3 groups, respectively. At D60, the immunocastrated animals also showed an increase in spermatozoa defects (P < 0.05), whereas plasma testosterone concentration decreased (P < 0.05). Immunocastration of lambs using the Bopriva vaccine at doses of 1.0 and 0.5 mL is efficient in inducing azoospermia in up to 80% of animals, although two doses in a 30-day interval are necessary for it to be an effective and safe method. Efficacy was demonstrated through a reduction in serum testosterone levels, testicular biometry, and seminal fluid analysis. Considering the efficacy of both doses in this study, we recommend using the lower dose (0.5 mL), which will allow for a 50% reduction in vaccine costs.
Highlights
Immunocastration occurs when the animal’s immune system is stimulated to produce specific antibodies against the endogenous gonadotropin-releasing hormone (GnRH) (Tesema et al, 2019)
At D60 after anti-GnRH vaccination, all testicular biometric variables presented a difference among treatments (P < 0.05) (Table 2), with the immunocastrated groups (1.0 and 0.5 mL) showing a reduction in the measured variables
The effect of vaccination was apparent after the second dose of the anti-GnRH vaccine in both treatments
Summary
Immunocastration occurs when the animal’s immune system is stimulated to produce specific antibodies against the endogenous gonadotropin-releasing hormone (GnRH) (Tesema et al, 2019) Through this immunization, endogenous GnRH is neutralized, causing indirect suppression of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and gonadal steroid release, affecting spermatogenesis (Han et al, 2015). Endogenous GnRH is neutralized, causing indirect suppression of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and gonadal steroid release, affecting spermatogenesis (Han et al, 2015) This technique has been shown to be an effective alternative to manual castration in animal production systems (Thompson, 2000), where males are routinely castrated for social and sexual behavior control and to improve carcass quality.
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