[GnRH agonist implants in small animal practice - what do we know 13 years following EU registration?]

The availability of GnRH agonist implants offers the possibility of a reversible, temporary downregulation of endocrine and germinative testicular function in male dogs and hobs. This review provides an overview of the registered indication, the induction of temporary infertility in healthy, intact, sexually mature male dogs (4.7 and 9.4 mg deslorelin) and hobs (9.4 mg deslorelin) as well as various off-label indications. Off-label use requires strict indications, informed consent from the owner and a lack of licensed medication (safe and optimum effect). Off-label indications in the male dog include sexual-hormone dependant (disturbing) behavior, benign prostatic hyperplasia, small adenomas of the hepatoid glands and alopecia X. Successful use of deslorelin implants for estrus suppression in jils, but also for the treatment of hyperadrenocorticism in ferrets in general have been described. Similarly, hormonal castration can be induced in tomcats and queens. The variable time to onset of effect and its duration (extremely variable in some animals) represent a challenge for breeders. No (sufficient) contraceptive activity was identified in male rabbits and male guinea pigs; however, treatment did successfully suppress the estrus cycle in female individuals of these species, as well as reproductive activity in male and female rats. Regarding the use in birds and reptiles, significant species-specific differences exist with regard to efficacy, time until onset of effect and duration of downregulation. In birds, the implant is efficient to fully suppress egg laying in chicken, Japanese quail and psittacids. In doves, egg laying is only significantly reduced. Successful treatment of reproduction-associated (unwanted) behaviour patterns (feather picking, aggression) has also been described. In some male birds, namely zebrafinch and Japanese quail, the deslorelin implant is suitable to reduce testosterone levels. Successful treatment of hormone-dependent tumours (Sertoli-cell tumorus) in budgerigars has been described as well as the modulation of specific behavior in turkeys and an efficacy in facilitating their keeping (i. e. reduction of aggression). In reptiles, only the successful use of deslorelin in iguana has been demonstrated to date.