Treatment with a subcutaneous GnRH agonist containing controlled release device reversibly prevents puberty in bitches

In most species, continuous administration of GnRH agonists desensitizes the pituitary to GnRH, and blocks ovarian function. The aim of this study was to assess the effects of a novel controlled release device containing azagly-nafarelin (Gonazon®) to prevent puberty in young Beagle bitches (mean age: 4.88 ± 0.32 months). Gonazon® containing 18.5 mg azagly-nafarelin (n = 10) or a placebo implant (n = 10) was administered subcutaneously. Throughout the 1-year treatment, estrus behaviour was monitored weekly. Plasma progesterone concentrations, as well as body weight and height, were measured monthly. Following implant removal, estrus detection and progesterone measurement were continued until occurrence of puberty in all bitches. Control bitches displayed puberty (estrus, followed by ovulation) at approximately 11.9 ± 2.7 (range, 8–16) months of age. In contrast, none of the Gonazon® treated bitches displayed puberty during the period when Gonazon® was present. Following removal of Gonazon®, resumption of estrus and ovulation naturally occurred (seven bitches) or was induced (three bitches) approximately 8.5 (1.2–14.3) months later. As a consequence, age of puberty of the Gonazon® treated bitches was 25.5 ± 5 (18–31) months. No clinically detectable side effects were noted in Gonazon® treated bitches. Height at withers was unaffected by treatment. Changes in body weight with time were also unaffected by treatment. Implants were well tolerated and generally easy to remove. These data demonstrated that Gonazon® safely, efficiently and reversibly prevents reproductive function for 1 year in prepubertal bitches.