Ferrets - Adrenal Gland Disease

What is adrenal disease?

It describes tumours or hypertrophy (excess growth) of the adrenal gland(s). Tumours may be benign (adenoma) or malignant (adenocarcinoma). In the latter case, spread may be localised or metastatic (with the liver being a common site for secondary tumours).

Causes

The root cause is in the ferret’s seasonal breeding cycle. This is initiated by increasing day-length causing changes in melatonin production. This stimulates release of Gonadotrophin-releasing hormone (GnRH) hence luteinising hormone (LH) and follicular-stimulating hormone (FSH) leading to:

Males – testicular descent and enlargement; weight gain; increased activity of sebaceous glands (skin becomes more greasy and increased scent).

Females – follicular development in ovaries, vulval enlargement. The female is an induced ovulator so will remain “in season” until mating. In captivity, failure to mate will result in prolonged exposure to oestrogen and a potentially fatal anaemia.

Problems occur in neutered ferrets (especially those neutered before puberty).

In these ferrets the day-length changes still induce a hormone cascade. However, there are no gonads on which to act. The adrenals, however, are stimulated to produce androgens and/or oestrogens, but not in sufficient quantity to induce a negative feedback effect on the pituitary gland.

Hence, the adrenal is subjected to a long-term, low-level stimulation and eventually becomes hyperplastic or neoplastic. By this stage hormone production is high but the adrenal is producing hormone independent of stimulation.

Other factors have also been linked to this condition:

• Diet.  More reliance on commercially produced pellets rather than a natural carcase-based diet. Perversely It is also mooted that these diets have resulted in increased longevity of ferrets (malnutrition used to be a serious problem) and that the higher incidence of tumours is simply an ageing effect.
• “Pet management”.  More keeping of ferrets indoors may alter the natural annual light cycles and so be a factor in adrenal stimulation.
• Genetics. Increased breeding of certain lines may increase tumour susceptibility. In this author’s experience, adrenal disease typically occurs in the older (over 5 years) ferret whereas in the US it is often present in much younger animals. This may due to breeding from very restricted lines but could also be due to American neutering policies where most/all pet ferrets are neutered by 8 weeks old.

Nonetheless it is neutering that appears to be the major cause of adrenal gland disease.

Clinical signs

The classic sign is that of a progressive alopecia. Initially, this is similar to that seen in “in season” jills and males in late summer/autumn. However, it will progress to affect the whole body.

Some may be pruritic and skin thinning may be seen in some cases.

Other signs may include neutered jills coming back into season with vulval swelling becoming obvious, and dysuria in males due to prostatic enlargement. Occasionally polyuria-polydipsia is seen.

Weight loss and abdominal swelling are apparent as the condition progresses.

Blood tests for sex hormones are useful but hard to get done. Tests for canine Cushing’s Disease are NOT appropriate.

"Blood tests for sex hormones are useful but hard to get done."

These signs in a neutered ferret should raise suspicions enough to justify further investigation including exploratory surgery of the abdomen.

The ideal treatment is to remove the affected gland.

Where malignant spread has already occurred or in recurrent cases surgery is not appropriate so medical management may be attempted. This currently involves Gonadotrophin releasing hormone (GnRH) analogues. Drugs intended for canine Cushings are not appropriate.

Prevention

Naturally, this should be our goal. Breeding from frequently-affected lines should be stopped and we should closely investigate the role of diet and controlled light cycles.

Should we be neutering ferrets?

In the case of jills, alternatives are available including annual “jill jabs” to bring them out of season. The issue is less easy for males which, because of their size and smell, are very unpleasant to live with. This of course raises the issue of should we keep pets that must be surgically altered to facilitate keeping? Hopefully current research into “chemical castration” including use of Gn-RH blockers will prove of value.

Neutering ferrets later, i.e. after puberty, will delay onset of disease but not prevent it.