Preliminary analysis of hormonal and seminal sperm parameters of subfertile and fertile stallions treated with the GnRH agonist lecirelin

Abstract

Subfertility is relatively common in stallions and few treatments are available to improve the semen characteristics of affected animals. The GnRH therapy, however, has been reported to improve sperm quality in individual clinical cases. The aim of this study was to evaluate therapeutical effects of daily GnRH analogue lecirelin treatment on sperm characteristics of fertile and subfertile stallions and to assess differences in the endocrine response among groups. Stallions were divided into untreated (n=3), fertile control (n=4) and subfertile (n=4) groups. Fertile and sub-fertile stallions received saline or 0.05 mg lecirelin, respectively, daily for 60 days and were evaluated for >90 days post-treatment. Ejaculates were collected biweekly, but semen and serum samples were evaluated weekly. Fertile stallions were characterized as having normal seminal parameters and a 75% conception rate. Subfertile stallions had low total and progressive motility (< 50% and 20%, respectively), sperm count, abnormal morphology (>30% of major defects), and ≈20% conception rate in the previous breeding season. Testicular response was assessed by determination of the concentrations of testosterone and estrone sulphate (interstitial compartment), anti-Müllerian hormone (AMH) and inhibin-B (tubular compartment) and correlated with sperm kinetics and production. Sperm kinetics were evaluated by CASA (IVOS Version 12 Hamilton Thorne Research, MA, USA), sperm concentration by Neubauer hemocytometer (Optik Labor®, Lancing, England), serum concentrations of inhibin- B, AMH and estrone sulfate weredetermined by ELISA and testosterone by RIA. Data were analyzed by ANOVA for repeated measures. In the subfertile group, testosterone concentrations decreased from week 0 to 6 (667 vs 302 pg/ml, respectively P<0.05), but tended to recover 1 month after treatment ceased (469 to 977pg/ml, respectively, P<0.08). Concentrations of all hormones were positively correlated with one another and with total sperm number (P<0.01), the highest between inhibin-B and estrone sulphate (R2=0.72) (P<0.01). No statistically significant effects on other hormones or semen characteristics were detected irrespective of group. Despite non statistical difference between groups, it is important to note that total sperm number increased by 60% 30 days after the beginning of the treatment and remained elevated by the end of the evaluation period in the fertile group. These data suggest that the treatment increased sperm production, but further investigations are underway. In conclusion, lecirelin treatment did not affect hormonal and seminal parameters in treated stallions, and did not affect testicular function. The correlation between hormones and sperm output indicates that these hormones are potentially valuable biomarkers for testicular function. Acknowledgements: São Paulo Research Foundation (FAPESP, grant #2019/01119-8 and #2022/03405-0), John P. Hughes Endowment and Clinical Endocrinology Laboratory, UC-Davis.