Surgical Proceedures in Pet Ferrets
by Anna Meredith MA VetMB CertLAS DZooMed MRCVS Royal [Dick] School of Veterinary Studies
Ferret anatomy is similar to that of the cat and dog with the following exceptions. Ferrets are monogastric like cats and dogs, however they lack a caecum (pouch at beginning of large intestine), with the ileocaecocolic (ileum, caecum and colon) junction being indistinct. The division may be identified visually by comparing the pattern of the intestinal blood vessels, which are radiating in appearance in the small intestine and linear in the large intestine. Ferret skin is relatively thick, to withstand bites from other ferrets. It has a thick subcutis. The abdominal musculature is relatively thick and care should be taken when making an incision for laporotomy, intra-abdominal fat deposits may be large and obscure structures such as the adrenal glands, ovaries and ureters.
This procedure is commonly carried out in the United States in female ferrets as young as 5 - 7 weeks old. It has been postulated that this may be a factor involved in the high incidence of neoplasia (tumours) in the American ferret population. Hyperoestrogenism is probably the most common endocrine condition encountered in practice in ferrets in the United Kingdom. Female ferrets are induced ovulators with seasonal polyoestrus (have more than one oestrus cycle in a breeding season). The normal breeding season for ferrets is between March and September. Ovulation occurs approximately 30 - 40 hours following mating. If unmated or not stimulated to ovulate, then as many as 50% of feales may develop aplastic anaemia after prolonged oestrus (up to six months). High levels of oestrogen lead to oestrogen suppression of the bone marrow and resulting anaemia with pancytopaenia (reduction in red and white blood cells and platelets). Other causes of hyperoestrogenism include, rarely an overian remnant following ovariohysterectomy, or more commonly, adrenal neoplasia. Pseudopregnancy following a sterile mating has been recorded in ferrets.
This condition is easily prevented in female ferrets by routine ovariohysterectomy, mating with a vasectomised male, or by use of proligestone (Delvosteron - Intervet UK.) subcutaneous injections, prior to the onset of the breeding season. This product (Delvosteron) is licensed for use in ferrets in the UK. Megoestrol Acetate can also be used to prevent onset of oestrus, but it should be noted that both of these drugs have been associated with the development of pyometra (uterine infection) and liver disease. Tamoxifen has antioestrogenic effects in humans, however, this is oestrogenic in ferrets and should therefore not be used. Altering of light cycles may prevent the onset of oestrus in jills (14 hours light; 10 hours dark).
Intact female ferrets, if they are not to be used for breeding, should be spayed from 5 months and preferably before their first oestrus. The ferret uterus is bicornuate (upper parts remain separate, lower parts fused into a single structure) and similar to cats and dogs. Ovariohysterectomy is carried out using a mid line ventral abdominal incision over the mid point between the umbilicus and the pubis. As mentioned previously large abdominal fat deposits may make visualisation of the ovaries and ureters difficult. Ferrets are elongated animals and with adequate exposure the author finds ovariohysterectomy a straight forward procedure. The suspensory ligaments are incrediably slack and do not need to be broken down. Care should be taken not to tear them and the ovarian blood vessels. The author uses a triple clamp technique with single ligatures for the ovarian blood vessels. Either 2-0 or 3-0 absorbable suture material is used. The uterine body is double clamped, ligated and the uterus and ovaries removed. Abdominal closure is routine as for other species. Ferrets rarely chew their sutures, although the author prefers to use a continuous subcuticular suture pattern. Antibiotics are not routinely given and the wound is examined again 7 - 10 days later.
Female ferrets may present with vulval swelling post spaying and it is possible in these cases that an ovarian remnant remains. The author has never seen this in practice, but extreme care should be taken to remove the ovaries in their entirety.
Pyometra and stump pyometra are rarely encountered in female ferrets. Surgical management is as for other species. In cases of pyometra the uterus is extremely friable and care should be taken to avoid rupture on handling.
This should be carried out in male ferrets at 6 - 8 months old. It may be of benefit in aggressive pets and also to reduce the sebaceous gland secretions, which produce the ferrets musky odour. Rarely testitular neoplasia is encountered (interstitial cell and ser-toli cell tumours).
The testes are situated caudoventrally (underside, near the tail) in the scrotal sac, a similar anatomical position to cats. There are two castration methods, which may be used.
The ferret is placed in the sternal recumbency (lying on their belly with back legs tucked under) and the hair is shaved over the scrotal sacs. I prefer to pack the anus with cotton wool to prevent anal gland secretions contaminating with the operation site. Remember to remove this afterwards! Bilateral longitudinal incisions are made over each scrotal sac and either a closed or open castration is performed. The open 'self-tie' precedure may be used, however I prefer to use a closed technique using double clamps and a single ligature. 4-0 absorbable suture material is used. The scrotal incisions are left open.
The other method is to place the ferret in dorsal recumbency (lying on their back, back legs apart) and the prescrotal area is clipped and surgically prepared. The castration is performed through either a single or double prescrotal incision, similar to the technique described for dogs. Open or closed techniques may be used again, and double clamps and a single ligature. I prefer to suture the prescrotal incisions using a subcuticular layer, however these may be left open.
Recently castrated and vasectomised male ferrets should be kept apart from the female for up to six weeks post-operatively to allow healing and prevent possible matings, which may occur in the author's experience up to four weeks post surgery.
More commonly owners request that their pet is vasectomised. This retains the ferret's urge to mate, however the mating is infertile and brings the female out of oestrus. The female may then be bred at a later date with an entire male. Aggressive behavour and odour will however remain.
The ferret is placed in the dorsal recumbency and the prescrotal area is clipped and surgically prepared. The vasectomy is performed through two prescrotal incisions, one for either side. The cord is palpated prior to making the incision. There is a deep layer of subcutaneous fat in this area which needs to be dissected through. The cord may then be visualised. The author finds that gentle traction on the testes helps to locate the cord through the fat. Extreme care should be taken to avoid the uretha. Once the cord is located it is exteriorised using a pair of artery forceps, which are looped under it. A careful incision is made in the tunica (membrane) to expose the vas deferens (tubes that carry sperm) medially. This may have a small vessel associated with it, but is distinct from the vascular plexus (network of blood vessels) and cremaster muscle, which are placed laterally. The vas is papable as a firm thickened band, which may be rolled across your finger. Ligatures are placed 1 to 11/2 cms apart and the cord between them is excised. I prefer to suture one end of the ligated cord into the tunica on closure to further prevent re-anastomosis (reuniting). The tunica is closed using a continous absorbable suture pattern. Closure may be difficult if the vascular plexus has become engorged, and this should be carefully pushed down as the tunica is closed over it. Single continuous absorbable sutures are placed in the subcutaneous fat and subcutis. The procedure is repeated the other side. Scrotal swelling is common post-operatively and may require anti-inflamatory treat-ment and analgesia for two to three days.