Vaccination against GnRH as a prelude to surgical castration of horses

A scoping review on intraoperative and postoperative surgical castration complications in domesticated equids

BACKGROUND

Castration is the most common surgical procedure in domesticated equids; surgical techniques used and perioperative management vary considerably.

OBJECTIVES

To identify and chart the current evidence on perioperative complications associated with different methods of surgical castration in domesticated equids.

STUDY DESIGN

Joanna Briggs Institute systematic scoping review.

METHOD

CAB Abstracts, Medline and Embase databases were searched using terms related to equine castration complications. Two authors independently and blindly screened publications against eligibility criteria. Data on study methods, perioperative management, surgical techniques, and perioperative complications were extracted. Surgical techniques were grouped into categories depending on technique; open, closed or half-closed, and whether the parietal tunic was open or closed at the end of surgery.

RESULTS

The search identified 1871 publications; 71 studies met the final inclusion criteria. The data reported 76 734 castrations, most of which were open or closed, with the vaginal tunic remaining open at the end of surgery. Twenty-five studies reported information regarding surgical techniques and perioperative management, allowing detailed charting and comparisons, of which analgesia and antimicrobial usage varied notably. Eighteen different complications were reported, with swelling or oedema being the most common. Evisceration was most commonly reported in draught breeds and Standardbreds, and the risk appeared low if the parietal tunic was closed at the end of surgery.

MAIN LIMITATIONS

Grey literature and studies not available in English were not included. Existing studies varied greatly in perioperative management, surgical techniques and reporting of outcomes, making evidence consolidation problematic.

CONCLUSION

A lack of consensus regarding complication definitions creates uncertainty and discrepancies between complication rates associated with different surgical techniques and perioperative management. The implementation of standardised systems for describing surgical techniques and complications is recommended for future studies. A number of studies did not follow current recommendations for perioperative analgesia and use of antimicrobials.

Endocrine changes induced by GnRH immunisation and subsequent early re-stimulation of testicular function with a GnRH agonist in stallions

CONTEXT

Resumption of testicular function after gonadotrophin-releasing hormone (GnRH) immunisation varies among individual animals and some stallions regain fertility only after a prolonged time.

AIMS

This study evaluated endocrine effects of GnRH immunisation and early subsequent re-stimulation with a GnRH agonist. We hypothesised that GnRH agonist treatment advances resumption of normal endocrine function in GnRH-vaccinated stallions.

METHODS

Shetland stallions were assigned to an experimental and a control group (n =6 each). Experimental stallions were GnRH-immunised twice, 4weeks apart. Each experimental stallion was hemicastrated together with an age-matched control animal when testosterone concentration decreased below 0.3ng/mL. Three weeks later, daily treatment with the GnRH agonist buserelin was initiated (4μg/day for 4weeks followed by 8μg/day). The remaining testicle was removed when testosterone concentration exceeded 0.5ng/mL in vaccinated stallions. Blood was collected for LH, FSH, oestradiol and anti-müllerian hormone (AMH) analyses, and testicular and epididymal tissue were conserved for real-time qPCR and histology.

KEY RESULTS

GnRH vaccination reduced blood concentrations of LH and FSH, with a structural deterioration of testicular tissue and disruption of spermatogenesis. Daily buserelin treatment for approximately 60days partially restored gonadotropin secretion and induced a recovery of the functional organisation of the testicular tissue with effective spermatogenesis.

CONCLUSIONS

Endocrine testicular function can be restored in GnRH-vaccinated stallions by daily low-dose buserelin treatment. The buserelin treatment protocol may potentially be improved regarding the dose, interval and duration.

IMPLICATIONS

Daily buserelin treatment can be recommended for treatment of GnRH-vaccinated stallions with prolonged inhibition of testicular function.

GnRH-immunocastration: an alternative method for male animal surgical castration

Castration of male animals is intended to produce high-enhance quality of animal meat, prevent unpleasant taste, reduce aggressive behavior, and manage overbreeding. Over the years, Tranditional methods of mechanical and surgical castration have been employed over the years, but they fall short of meeting animal welfare requirements due to the associated risk of infection, pain, and stress. Immunocastration, specifically Gonadotropin-releasing hormone (GnRH)-immunocastration, targeting the hypothalamic-pituitary-testis (HPT) axis, has emerged as an animal-friendly alternative to surgical castration, effectively addressing these issues. This review seeks to systematically summarize the principles, development, current applications and challenges of GnRH-immunocastration, offering insights into its role in promoting animal welfare.

Immunocontraception of male domestic cats using GnRH vaccine Improvac

The domestic cat is a highly prolific species; thus, reproductive control is crucial to reducing feral cat overpopulation. This study aimed to assess the effect of a commercially-available GnRH vaccine for swine on suppressing sperm production in male cats. Twelve sexually mature tomcats were randomly divided into two groups. Treated cats (n = 9) received a GnRH vaccine (Improvac, Zoetis Belgium SA, 0.5 mL sc) twice 4 wk apart, and the control group (CON, n = 3) saline solution (0.5 mL sc). Reproductive parameters and blood samples were recorded every 2 wk, from 6 wk before vaccination until 24 wk after the first dose. Day 0 of the study was defined as the day of primary immunization with either the vaccine or saline solution. Serum testosterone concentrations of treated cats dropped to basal levels 6 wk after D0, while CON cats maintained serum testosterone concentrations between normal ranges during the study period. No differences were observed in pretreatment and CON seminal samples. However, a progressive decrease in seminal quality was observed in treated cats from wk 8 until the end of the study. By wk 24, sperm concentration and total sperm count decreased by 90%, motility decreased by 70%, and viability decreased by 60%. Moreover, testicular volume was reduced by 49%, and penile spines showed almost complete atrophy by the end of the study. Although treated cats showed a decrease in the hematocrit, erythrocyte count, and hemoglobin concentration, values were within the reference range for domestic cats. No differences were observed in the other hematological and biochemical parameters evaluated. Our results agree with previous immunocontraception studies in cats, showing that Improvac vaccination effectively reduced sperm quality, testicular volume, and serum testosterone concentration. Further studies should be carried out to define the Improvac long-term effect.

Re-stimulation of testicular function in GnRH-vaccinated stallions by daily GnRH agonist treatment

In stallions temporarily not intended for breeding, reversible suppression of testicular function by vaccination against GnRH can be of interest. In the present study, effects of GnRH agonist treatment on the resumption of testicular function after GnRH vaccination were investigated. Testis size, testosterone release, semen characteristics and behavior were evaluated. We hypothesized that GnRH agonist treatment would restore testicular function. Shetland stallions were assigned to an experimental and a control group (n = 6 each). Experimental stallions were GnRH-immunized twice, four weeks apart. Ejaculates for semen analysis and blood for analysis of testosterone concentration and GnRH antibody titers were collected. Each experimental stallion was hemicastrated together with an age-matched control animal when testosterone concentration decreased below 0.3 ng/mL. Three weeks thereafter, daily treatment with the GnRH agonist buserelin was initiated (4 μg/day for 4 weeks followed by 8 μg/day). The remaining testicle was removed when testosterone concentration exceeded 0.5 ng/mL in vaccinated stallions. Time from exposure to a mare until mounting increased in GnRH-vaccinated stallions and decreased with buserelin treatment. Total sperm count decreased after vaccination but increased only slightly in response to buserelin. Sperm motility and percentage of membrane-intact spermatozoa decreased after vaccination and returned to pre-vaccination values with buserelin treatment. Testosterone concentration and testis volume decreased after GnRH vaccination and started to increase with buserelin treatment. In conclusion, the downregulation of testicular function by GnRH vaccination can be counteracted with buserelin. This approach may be useful in GnRH-vaccinated stallions with prolonged suppression of testicular function.