SURGICAL NEUTERING of domestic ferrets (Mustela putorius furo) is common in the United States and various European countries. Female ferrets (jills) are induced ovulators, so they remain in estrus until they are mated or for as long as daylight lasts longer than 12 hours. In the early 1980s, several articles appeared concerning estrogen-induced bone marrow suppression in jills with prolonged estrus.1,2 Since then, preventive ovariectomy or ovariohysterectomy of jills has been advised. In male pet ferrets (hobs), there is no medical need for castration. The main reason to castrate hobs is to reduce aggression so that they can be kept in groups and to decrease the intensity of the musky odor produced by the sebaceous glands.3 In the United States, it is common to neuter ferrets at 6 weeks of age, before their delivery to pet shops.4
1. A 4-year-old neutered female ferret showing dorsal alopecia. No swelling of the vulva is noticed.
Hyperadrenocorticism, a common disease among pet ferrets, is characterized by signs of excessive production of sex steroids (androstenedione, 17-alpha-hydroxyprogesterone, dehydroepiandrosterone sulfate, and estradiol), such as symmetric alopecia (Figure 1), vulvar swelling in neutered jills, and recurrence of sexual behavior in neutered ferrets.4-7 In recent years, evidence has accumulated that hyperadrenocorticism in ferrets is mediated by an increased secretion of gonadotropic hormones after castration4,6:
- First, the initial signs of hyper adrenocorticism occur only during the breeding season,8 when plasma concentrations of gonadotropic hormones are high.
- Second, in the United States and in The Netherlands, where neutering of ferrets is common, hyperadrenocorticism is common.6,8 In contrast, adrenal gland tumors are considered unusual in the United Kingdom,9 where ferrets often remain intact.10
- Third, a significant correlation has been found between the age at neutering and the age at onset of hyperadrenocorticism.6
- Fourth, the gonadotropin-releasing hormone (Gn-RH) analogue leuprolide acetate has had beneficial effects in treating this disease.11
- Finally, luteinizing hormone (LH) receptors have been detected in the adrenal cortex in ferrets.12
Because evidence points to surgical neutering as an important risk factor for hyperadrenocorticism in ferrets, we reviewed the literature to find current and possible future alternatives to surgically neutering ferrets (Table 1). Most of the information we have provided here is based on species other than ferrets. Only after studies have been performed in ferrets can conclusions be drawn on whether these techniques are effective in this species.
Possible Alternatives to Surgical Neutering in Ferrets
Gonadal activity is seasonal in both male and female ferrets, and more than 12 hours of light a day promotes reproductive activity.13 The pineal hormone melatonin seems to play a central role in regulating these changes.14 Plasma and pineal gland melatonin concentrations are significantly higher during the dark phase of the day (scotophase) than in the light phase (photophase). Therefore, it has been suggested that this hormone has an inhibitory effect on Gn-RH release.15
During the breeding season, Gn-RH stimulates the production of the gonadotropic hormones LH and follicle-stimulating hormone (FSH), which stimulate the gonads to produce either estradiol or testosterone. The latter two hormones exert a negative feedback on the hypothalamus and pituitary gland, thereby preventing excessive secretion of Gn-RH, LH, and FSH.