Chronic use of a GnRH agonist (deslorelin) or immunization against GnRH: effects on testicular function and sperm quality of bucks

Abstract

Chronic use of GnRH agonists and immunization against GnRH have been used as reversible contraceptive methods. The aim of this study was to compare the effectiveness of both treatments to inhibit reproductive function of adult bucks, in terms of strength and duration of the effects. We used 9 control untreated bucks (CON), 7 bucks treated chronically with a GnRH agonist (subcutaneous implants with 7.4 mg of deslorelin, Suprelorin, Virbac) (AGO), and another 7 bucks were immunized against GnRH (dose of 2 mL of Improvac-Zoetis with 300 μg of a synthetic incomplete analog of natural GnRH; 300 mg of diethylaminoethyl-dextran; and 2.0 mg of chlorocresol) (IMM). Testicular and sperm evaluations, testosterone concentrations, and male odor were determined from 4 wk before applying the treatments until 17 mo of their application. Scrotal circumference of CON (21.0 ± 0.1 cm) and IMM (21.2 ± 0.2 cm) was greater than that of AGO bucks (19.9 ± 0.2 cm) (P < 0.05 for each), without difference between CON and IMM bucks. Pixels' color intensity of testicular ultrasound images was not affected by treatment (general mean ± SEM: 116.0 ± 1.8). Testosterone concentration was greater in CON than AGO and IMM in months 3 and 4, greater in CON and IMM than AGO bucks in months 15 and 16, and greater in IMM than CON and AGO bucks in month 17 (P < 0.05 for all comparisons). Male odor was greater in CON (1.5 ± 0.0) than IMM bucks (1.3 ± 0.0) and greater in IMM than AGO (1.1 ± 0.0) bucks (P < 0.05 for each). Treatment negatively affected all the sperm variables: the total number of sperm in the ejaculate, sperm motility, sperm with normal morphology and sperm with integral membrane function. It was concluded that both treatments were effective in inhibiting the reproductive axis; however, neither of them produced azoospermia or decreased testosterone concentrations to undetectable levels. With both treatments, there were individual males exhibiting characteristics of fertility in all periods of the study. However, chronic use of a GnRH agonist seemed to be the most effective treatment in terms of duration and strength.

Keywords: Contraception; GnRH agonist; GnRH immunization; Sperm characteristics; Testosterone concentration.