The ferret, Mustela furo, most likely descended from the Eurasian polecat through domestication around 2,500 years ago. The original reason for their domestication was likely for “pest” control, and of the current estimated captive population in the UK today (500,000), the majority are still used at least in part for this purpose. However, ferrets are also a common “exotic” mammal kept solely as a pet, though their reproductive behaviours can present a difficulty for both their owners and the veterinary team.
Ferret reproductive behaviours
Ferrets are sociable animals and are best kept in pairs or small groups. Ensuring that individuals are related to each other or are of the opposite sex is not normally needed when keeping ferrets in captivity, and if introduced appropriately, most ferrets will bond with their counterpart(s) (Figure 1). As such, simply housing a ferret alone is both unrequired and arguably ethically poor husbandry for such highly social animals (Keeble and Meredith, 2009). For most species, simply housing males and females apart prevents unwanted breeding and related complications; however, it is more complicated with ferrets. This is because female ferrets, or “jills”, are induced ovulators and therefore require a hob (male) to be housed with them if they are not undergoing medical or surgical intervention (Lindeberg, 2008).
Female ferrets, or “jills”, are induced ovulators and therefore require a hob (male) to be housed with them if they are not undergoing medical or surgical intervention
Jills are seasonal breeders, stimulated to come into oestrus under the influence of light (Jekl and Hauptman, 2017). Lengthening daylight hours induce the jills’ cycles, which normally begin around March time in the UK and the northern hemisphere and can last till September, when daylight length drops below 12 hours a day (KeebleandMeredith, 2009). Alongside mating, the process of ovulation is stimulated by the hob grabbing the jill by the scruff of the neck and dragging her. While this can appear aggressive, these stimuli are needed for ovulation to occur (Schoemaker, 2010).
Common physical signs of a jill being in season are a swollen vulva, vulval discharge and, if the season has gone on for an extended period, areas around the groin and inner thigh showing signs of ventral alopecia. Both hobs and jills also produce more oils in their skin, so developing an “oily” coat and an increase in their notorious odour are also signs of the jill being in season (Keeble and Meredith,2009). In turn, behavioural changes such as nesting can occur in jills, though this is more related to pregnancy or pseudopregnancy than a season itself.
The issue facing all ferret owners is that, as previously mentioned, ferrets rely on induced ovulation, so without the aforementioned stimuli occurring, jills will remain in a constant state of season, which can lead to medical complications (Fox, 1998). Without ovulation, the level of the hormone oestradiol increases, remaining at high levels until the jill’s season ends. Oestradiol is naturally important for the development of the jill’s reproductive processes; however, without stimuli to cease its release, the jill is at risk of alopecia and, more importantly, bone marrow suppression (Lindeberg, 2008). Persistent bone marrow suppression results in a marked reduction in blood cell creation and will lead to pancytopenia, which will result in death if left untreated (Fox, 1998). Some jills can go numerous seasons without being mated and seemingly appear fine, while others show signs of pancytopenia in their first season, so individuality plays a part in this process.
Oestradiol is naturally important for the development of the jill’s reproductive processes; however, without stimuli to cease its release, the jill is at risk of alopecia and […] bone marrow suppression
Treatment and interventions for ferret reproduction
In the past, surgical spaying of the jill or castration of the male was the go-to treatment to prevent persistent cycling; however, in 1987, the first cases of hyperadrenocorticism were reported, and a link between surgical neutering and these cases were found (Keeble and Meredith, 2009). It is important to note that hyperadrenocorticism does not solely occur as a result of surgical neutering; however, there is undisputedly a high risk of occurrence in neutered ferrets of both sexes (Fudge, 2000). Furthermore, in 2003 adrenal disease was found to occur in 70 percent of ferrets in America, often leading to fatalities if left untreated (Fudge, 2000).
Of course, all these issues with ferret reproduction can be “solved” by simply putting in an entire hob and allowing them to mate as they would naturally. This will cause the jill to ovulate and therefore solve the problem of pancytopenia. In turn, however, you then have a litter of kits (baby ferrets) which may not be an ideal solution for the owner, especially as this would need to be repeated year after year. So, the original problem then becomes what to do for the jill if you do not want to breed from her. A ferret’s natural cycle requires a male stimulus to finalise, and as neutering of either sex is not without risk, both from the anaesthesia and surgery and then from any future medical complication, the solutions can appear less clear.
Hyperadrenocorticism does not solely occur as a result of surgical neutering; however, there is undisputedly a high risk of occurrence in neutered ferrets of both sexes
The first option is to vasectomise the hob, which will allow the male to produce the same number of hormones and have the same desire to mate with a jill but will not increase the risk of adrenal disease or adrenal tumours. A vasectomy is also good for the jill as her ovulation can still be induced, though the hob has the risks associated with anaesthesia, surgery and recovery (Schoemaker, 2010). The hob will also still go through its breeding season changes, which can be off-putting to owners. In turn, the jill can go through pseudopregnancy behaviours as she feels she will become pregnant. These behaviours can lead to aggressiveness and may require separation from the hob alongside the cessation of handling from the owner.
The second more popular option is hormone treatment via an implant. Deslorelin implants allow hormone production to be ceased, helping the jill leave her oestrus cycle (Figure 2). However, it can take two weeks for the complete cessation of her season post-implantation. Deslorelin implants last around 18 to 24 months, but individual differences are seen depending on the strength provided, etc (Schoemaker, 2010). In the past, a proligestone “jill jab” was often used at the start of a jill’s season, but these are becoming less popular for multiple reasons. Implants require anaesthesia for safe placement, and though brief, this is not without risk.
In the UK, deslorelin implants are licensed for hobs but not for jills, though they are commonly used for both sexes (Jekl and Hauptman, 2017). Many veterinary practices in the UK report very good success with these implants, and despite being comparatively expensive due to their need for repeated implants, many ferret owners now prefer this option too.
Ferrets have a fairly unique breeding style in the world of domesticated exotic pets, and these can present significant challenges. While ferrets have a range of commonly seen conditions in practice, a number of them can be attributed to reproductive disorders if the ferret’s behavioural physiology needs are not correctly met. Considerations must be taken based on individuality of patient needs; however, concurrently with this, owners’ expectations of treatment and outcomes must also be met as the options for intervention can be varied.