What Happens in Male Dogs after Treatment with a 4.7 mg Deslorelin Implant? I. Flare up and Downregulation

SIMPLE SUMMARY: Until now, information about the “flare up” and the time to downregulation in male dogs after treatment with a 4.7 mg deslorelin implant is strongly limited, regarding testosterone concentrations, testicular and prostatic volume and semen quality. The aim of this study was to provide detailed insights into these open questions. GnRH and hCG stimulation tests were performed to gain further insights into testicular endocrine function. Seven male beagle dogs were treated with a 4.7 mg deslorelin implant, and three animals were treated with saline, representing the controls. In deslorelin-treated dogs, first basal testosterone concentrations were observed earliest on D7 and latest on D28 after treatment. Infertility—based on the lack of semen or spermatozoa— was diagnosed earliest on D35 and latest on D77. After five months, the treatment was still effective in six dogs but was reversed in one deslorelin-treated dog. ABSTRACT: Although registered since 2007, knowledge about changes in testosterone concentrations (T), testicular and prostatic volumes (TV, PV) and semen quality, as well as the time point of infertility following treatment with a 4.7 mg deslorelin (DES) slow-release implant, is limited. Therefore, seven sexually mature male dogs were treated with DES (TG); three male dogs treated with saline served as controls (CG). The study assessed local tolerance, TV, PV, semen parameters and T subsequent to GnRH/hCG stimulation in regular intervals. Local tolerance was good. In TG, T was increased right after treatment, but decreased four hours afterwards. Subsequently, TV, PV, semen quality and T decreased over time in TG, but not CG. T was basal (≤0.1 ng/mL) from D28 onwards. Response to GnRH/hCG stimulation was variable, with two TG dogs having increased T post-stimulation on all study days independent of pre-treatment concentrations. A(zoo)spermia in TG was observed from D35–D77 in all seven dogs. Whereas treatment was still effective in six TG dogs five months after implant insertion, it was fully reversed in one dog in terms of T and spermatozoa on the last examination. These results indicate high variation in individual dogs, necessary to consider when advising dog owners.