Abstract
Objective Slow-release GnRH agonist implants (SRI) are used for reversible
medical downregulation of testicular function in male dogs as an alternative to
surgery. The 4.7 mg deslorelin SRI should reduce testosterone after
6–8 weeks and induce castration-like effects for 6 months (mon).
However, some individual variation is described in the field in regard to onset
and duration of effect. For this reason, we aimed to study the effects of the
4.7 mg deslorelin SRI in a larger cohort.
Material and methods In total 50 intact, healthy male dogs (12–48
months, mon; 9–40 kg) were treated with a 4.7 mg
deslorelin SRI into the umbilical area (TG, n=45) or served as untreated
controls (CG, n=5). CG dogs were surgically castrated after measurement
of testicular dimensions and blood sampling for testosterone. In TG, SRIs
remained for 5 mon in place and subsequently 3–7 male dogs were
surgically castrated at removal (week, W 0) or 1, 2, 3, 4, 5, 6, 7, 8 or 10
weeks later. Examination parameters were testicular dimensions (before
treatment, at 4, 8, 12 W, 5 mon, weekly until castration), testosterone
(before treatment, at 8 W, 5 mon, castration) and testicular histology
(castration).
Results Whereas examination parameters did not differ between CG and TG
before treatment, testicular volume and testosterone was significantly reduced
at all time points during treatment. In all but 3 (8 W) and 2 male dogs
(5 mon) testosterone was basal during treatment before removal, whereas the
parameters were significantly reduced compared to pre-treatment in the
respective dogs. After implant removal, testosterone and testicular volumes
increased. However, different to earlier studies, the „restart“
was more variable with individual basal testosterone until W7, but also
physiological testosterone concentrations in W2. Similarly, histological
testicular findings at castration were quite variable: besides an arrest on
spermatogonia and spermatocytes, elongated spermatids with normal
spermatogenesis were found in individual dogs.
Conclusion Our study confirms the efficacy of the deslorelin SRI, but also
individual variation especially regarding reversibility of effects on endocrine
and germinative testicular function.
Clinical relevance Deslorelin SRIs offer a suitable alternative to
surgical castration with individual variation to be considered when used in
clinical practice.