Clinical Use of Long-Term GnRH Agonist in Prepubertal Bitches: Effect on P4, E2 and Melatonin Serum Concentration before and During First Estrus

The aim of this study was to determine the length of the contraceptive period after the application of deslorelin implant (4.7 mg) in juvenile, prepubertal bitches and assess the effects on the hormonal status (P4, E2 and melatonin), as well as on the occurrence of normal physiological estrus. Twelve crossbred prepubertal female dogs (4 months of age) were divided into the two groups, the treated group (DESLO) and control (placebo) group (C). Hormone assays, vaginal microbiological and cytological smears and the measurements of electrical resistance of cervical mucus were performed once in 3 weeks until the first signs of proestrus, and every day during estrus. GnRH implant significantly postponed time of onset of estrus (633 ± 30,38 days vs. 143.80 ± 52,30 days, P<0.001). In estrus, DESLO group showed statistically higher E2 (34.58 pg/mL vs. 20.59 pg/mL, P<0.001) and melatonin serum concentration (45.86 pg/mL vs. 18.85 pg/mL, P<0.001) compared to the control group. The average P4 serum concentration had no statistically significant differences between groups. In conclusion, deslorelin implants do not cause “flare up” effect in perpubertal bitches, however, increase of E2 and especially melatonin serum concentrations show the need to explore the consequences and mutual influence of melatonin and deslorelin implants in the future.