Reasons to neuter female rabbits
• To prevent unwanted litters.
• To reduce hormonal territorial behaviour and aggression
• To prevent false pregnancies.
• To prevent reproductive disease, which is very common and often silent in mature entire females. Uterine adenocarcinoma is
life-threatening and extremely common. It has been reported that 60% of entire females will have adenocarcinoma by the time they are 4 years old and 75% will have it by the time they are 7 years old (Greene, 1941).
become very closely bonded with their owners.
There is no medical reason to neuter these rabbits.
Most reproductive problems develop later in life and are i s t t e ner t is ti e t e ra it’s personality and behaviour is well established and castration is unlikely to alter it.
Suitable ages for neutering Females
Does can be neutered at any age, although the pro-cedure is more difficult in immature females because the uterine horns are tiny, threadlike, difficult to locate and may break if any pressure is applied (Figure 12.1). For this reason, it is preferable to leave females until they are hormonally active, usually at about 5 months of age. The easiest time to neuter females is between 6 and 9 months, before large amounts of fat are laid down in the mesometrium.
Reasons to neuter male rabbits
• To prevent breeding.
• To prevent fighting with other rabbits. Neutered male rabbits can live together companionably.
• To prevent undesirable behaviour such as urine spra in r inappr priate’ c p lat r acti ns
• To reduce sexual frustration and obsessive compulsive behaviour displayed by entire males that live on their own or in proximity with others.
• To reduce sexual behaviour towards a companion rabbit (or guinea pig, although this is not recommended as a good arrangement for either species).
• To treat male reproductive disease such as inguinal hernia, cryptorchidism, testicular neoplasia or testicular torsion.
The post-mortem appearance of the uterus of a 14-week-old female rabbit. The caecum, proximal colon and small intestine have been removed.
The small size of the vestigial uterus (white arrow) can be compared with the rectum (black arrow) that lies adjacent.
At this age the uterus is difficult to locate friable and easily broken as it is exteriorized, which makes ovariohysterectomy difficult.
12.1 Elective neutering is recommended for all female
rabbits that are not intended for breeding. However, no real health benefits are gained from neutering young male rabbits and so, if the rabbit is kept as a sole house rabbit, many owners prefer to leave them entire. Entire male rabbits tend to have a stronger personality than neutered ones and not all of them show undesirable male behaviour. Entire males that have a lot of interaction and companionship can
Ovariohysterectomy can be performed at any time during pregnancy or pseudopregnancy but after a doe has given birth it is preferable to delay surgery until the babies are weaned at 4–5 weeks old.
Males
Males can be neutered as soon as testicles are evident within the scrotal sacs, which can be as early as 10 weeks. Rabbits with absent testicles should be left until they are at least 6 months old to give time for the testicles to descend. There is no upper age limit for castration.
Female reproductive anatomy and physiology
Anatomy of the reproductive tract
A diagram of the female reproductive tract and its relationship with neighbouring organs is shown in Figure 12.2. Both ovaries lie in the dorsal abdomen, close to the kidneys. They are elongated elliptical structures that, in a sexually mature female, contain multiple follicles at varying stages of development (Figure 12.3). The cranial end of the ovary is attached to the fimbriae, which open into the infundibulum. This is attached to the ampulla tubae uterinae, which forms a semicircle that encloses the ovary. These structures are enclosed in a discrete body of fat, the mesovarium, which is part of the mesometrium.
The caudal end of the ovary is attached to the mesovarium by a short ligament. The fallopian (uter-ine) tube is long and red in colour and can resemble a blood vessel. It opens into a long convoluted
Kidney
Distal
colon Uterine
horns Bicornuate
cervix
Ureter
Bladder Urethra
Genital opening Anus
Ovary Mesometrium
Rectum
Vagina
Infundibulum Fallopian tube
Anatomy of the female reproductive tract and its relationship with neighbouring organs.
12.2
An ovary that has been exteriorized during ovariohysterectomy. It contains follicles in various stages of development. The ovary is encompassed by the ampulla tubae uterinae, which is a deep red colour and resembles a blood vessel.
12.3
uterine horn, which ends in a cervix. The right and left uterine horns are completely separate so that the two cervices are attached to form a single struc-ture (bicornuate cervix) that separates the uterus from the vagina. There is no uterine body. The vagina is a long flaccid but muscular structure that fills with urine during micturition. Contractions of the vagina occur readily and may be seen during ovario-hysterectomy. The urethra lies ventral to the vagina and opens into it about half way along its length, beneath the pubic bone. The part of the vagina that is distal to the urethral opening (vestibulum vaginae) is attached to supporting musculature, which can constrict and move the vagina and vulva during uri-nation, mating and parturition.
Genitalia of 6-week-old female (a) and male (b) siblings. At this age, the testicles are not descended and it is easy to sex the rabbits incorrectly. The genital orifice needs to be retracted to e pose a the cone-shaped vulva with a slit-shaped opening or (b) a small tubular penis. The distance between the genital opening and the anus is greater in the male than in the female.
12.4
(a) (b)
Reproductive physiology
Rabbits are well known for their ability to reproduce quickly. As babies, they can be difficult to sex (Figure 12.4) but this becomes easier once they reach puberty at 4–9 months of age. Smaller breeds mature earlier than larger breeds.
maternal behaviour is minimal and the babies are left alone in the nest for most of the time. The doe only returns to the nest for less than 10 minutes once or occasionally twice a day to feed them. The entrance to the nest is stopped up with leaves, earth or bed-ding material and hidden between visits, so owners may be unaware of the existence of the babies or, if they find them, may think they have been deserted.
Owners may need reassurance that it is normal for their rabbit to be out of the nest when she has a litter and that she may be particularly aggressive and pro-tective during this period. Lactation takes place for approximately 5 weeks after parturition.
During lactation, the mother stays close to the nest and may attack potential intruders, including human owners. She is particularly susceptible to disturbance in the first few days after parturition and may cannibalize or mutilate the young if she is upset. The legs or ears may be bitten, or even removed, or the skin stripped from over the neck, thorax or abdomen.
Pseudopregnancy
Ovulation can take place without mating and result in pseudopregnancy. Ovulation can be stimulated by the proximity of other rabbits or by the act of being mounted by another female. Pseudopregnancy is shorter than true pregnancy, lasting approximately 16–18 days. During this period the doe may show many of the signs of late pregnancy, such as aggres-sion, pulling hair from the stomach and mammary development. Abdominal palpation and ultrasound examination are the best ways of differentiating the two conditions.
Female aggression
Female rabbits show many behavioural character-istics that are related to their hormonal status.
Sexual receptivity, pregnancy, pseudopregnancy and nursing a litter of babies can radically affect the temperament and behaviour of a female pet. In the wild, the choice of nesting site has a strong influ-ence on the survival of the young, and competition
The exteriorized uterus of a rabbit in
mid-pregnancy undergoing ovariohysterectomy.
Viable fetal units and a resorbing one can be seen. The resorbing fetal unit is much smaller than the rest (arrow);
dissection of the uterus showed that this unit contained a mass of amorphous tissue. The other units contained fetuses.
12.5
Rabbits are induced ovulators with no defined oestrous cycle, although a cyclic rhythm in sexual receptivity exists. Follicular development occurs in waves, with 5–10 follicles on each ovary at any one time (see Figure 12.3). When the follicles reach maturity they produce oestrogens for about 12–14 days; if ovulation has not occurred during this period the follicles then degenerate with a corresponding reduction in oestrogen level and sexual receptivity.
After about 4 days a new wave of follicles develops and the doe becomes receptive again. Mating stim-ulates ovulation approximately 10 hours after coitus.
The average litter size is 5–8 and females are able to conceive within hours of giving birth. Rabbits can be lactating while they are pregnant, and it is possible for a single female to give birth to over 40 offspring each year.
Pregnancy
Gestation lasts for 30–32 days. Pregnancy can be detected by abdominal palpation and the best time for diagnosis is 10–14 days after mating, when the fetal units can be felt as olive-sized masses. Fetal resorption is relatively common in rabbits and can take place up to 20 days post coitus. Sometimes viable fetuses are found alongside resorbing ones (Figure 12.5).
Mammary development takes place in late preg-nancy when the doe starts to prepare her nest by filling it with hay or other material before lining it with fur pulled from the hip, dewlap and mammary glands. After parturition, the doe pulls even more fur from her body to cover the litter in the nest. It is advisable to remove other rabbits from the hutch during late pregnancy.
Parturition
Parturition usually takes place in the morning and lasts less than 30 minutes. The babies are born blind, without hair and helpless. After giving birth,
for a good site is strong. Females will dig out a nest-ing chamber before they are pregnant and defend it from predators and other rabbits. Some female pet rabbits display this behaviour towards their owners and other rabbits or pets that come close to their chosen nesting site, which is often their hutch or sleeping area because they have no other choice.
To the owner, the transformation from an endearing baby rabbit to an adolescent one that strikes, growls or even bites when it is approached in its cage can be upsetting. Neutering can make a difference by removing the hormonal triggers for this behaviour.
Diseases of the female reproductive system
There are many diseases that can affect the female reproductive tract. The clinical signs that might alert the owner and practitioner to these problems are listed below. Diagnosis is confirmed by abdominal palpation, ultrasonography (see Chapter 8), abdom-inal radiography (see Chapter 7) and exploratory laparotomy.
Diseases of the female reproductive tract are more likely to be encountered as age increases. Many of the disorders show few obvious clinical signs until the condition is advanced. The clinical signs include:
• Palpable abdominal masses
• Abdominal distension
• Bleeding from vulva (may be sudden and severe)
• Haematuria. Blood from the uterus mixes with urine in the vagina so they are voided together.
Close observation shows more blood at the end of urination. Blood clots are suggestive of uterine disease
• Regenerative anaemia
• Serosanguineous or purulent vaginal discharge
• Urinary incontinence due to an enlarged uterus pressing on the bladder
• Behavioural changes, such as aggression or increased sexual behaviour
• Mammary development, tumours or cysts
• Abnormal appearance of vulva due to vaginal prolapse or bladder eversion
• Anorexia and weight loss in advanced stages of some conditions.
Radiography and ultrasonography are useful to gain more information and can help to different iate between the various conditions but lapar otomy is always necessary to treat the disorders.
Endometrial hyperplasia
Endometrial hyperplasia results from prolonged oestrogenic stimulation. It is characterized by thick-ening of the endometrium, development of mucus-filled glands and accumulation of mucus in the lumen of the uterus. It is common in entire female rabbits (Saito et al., 2002) and usually occurs in rabbits over 3 years of age, although it has been reported in rabbits under a year old (Walter et al.,
2010). The condition has few clinical signs and is usually discovered during elective ovariohysterec-tomy. A serosanguineous discharge may be noticed by observant owners. It is not clear whether endo-metrial hyperplasia progresses to uterine neoplasia or whether both conditions are hormonally stimu-lated and therefore have the same predisposing factor (Walter et al., 2010).
Uterine tumours
Adenocarcinoma of the uterine endometrium is the most common neoplasm encountered in rabbits.
The incidence increases with age and has been reported to reach 60% in females over 4 years of age and 75% by 7 years (Greene, 1941). Uterine adenocarcinomas are often multicentric and involve both horns of the uterus, appearing as globular polypoid structures that project into the uterus (Figure 12.6). As the condition advances, the tumours enlarge and coalesce so that large portions of the uterus are affected and they become pro-gressively more palpable. They may contain large areas of haemorrhage, necrosis or calcification.
Metastasis is slow and occurs via local spread into the peritoneum and other abdominal organs, such as the liver, or by haematogenous spread to distant sites, such as the lung, brain, skin or bones.
Not all uterine tumours are adenocarcinomas.
Carcinosarcoma, adenoma, metastasis from ovarian tumours, leiomyoma and leiomyosarcomas have also been reported (Saito et al., 2002; Walter et al., 2010).
A section of the uterus of a 5-year-old Dutch rabbit that had a palpable abdominal mass. The uterus was removed. The polypoid mass extended into the lumen and into the underlying muscle layers. This is the typical gross appearance of a uterine adenocarcinoma.
The diagnosis was confirmed histologically.
12.6
Pyometra
Pyometra is manifested by lethargy, inappetence, a purulent vaginal discharge, abdominal distension and a palpable abdominal mass. Pasteurella multo-cida is often present and pyometra has been cited as a manifestation of pasteurellosis (Johnson and Wolf, 1993). As in other species, pyometra is a life-threatening disease but is complicated in rabbits by the ready formation of adhesions between the infected uterus and other structures and the friability of the tissue. Rupture of the uterus can occur during surgery but surgery is the only option for treatment and can be successful.
Developmental abnormalities
Developmental disorders, such as absent uterine horns, are sometimes encountered during ovario-hysterectomy in rabbits. Other abnormalities, such as a rudimentary vagina or an absent cervix, have been reported. Some abnormalities occur concur-rently with other problems, such as absent kidneys (Thode and Johnston, 2009).
Endometrial venous aneurysms
Aneurysms of the uterine and myometrial venous plexuses can develop in some females, causing epi-sodic bleeding, which can be dramatic and fatal.
Intermittent haematuria may be evident.
Hydrometra
The clinical signs of hydrometra are loss of body fat and muscle and abdominal distension. There may be no change in bodyweight. The uterus is grossly enlarged (Figure 12.7) and filled with clear fluid. The condition occurs in mature females and can be diag-nosed by ultrasound examination. Ovariohyster ec-tomy is curative.
This ectopic fetus was found in the abdominal cavity during routine ovariohysterectomy.
12.8
Vaginal prolapse and bladder eversion Prolapse of the vagina or eversion of the bladder occasionally occurs in rabbits that have recently given birth. Affected does are presented with a mass protruding from the vagina. They may be straining and unable to urinate. Replacing the prolapsed organ and putting in a purse string suture around the vulva can be successful.
Infection of the perineum and vulvar skin folds
Infection in the skin folds around the genitalia is common in mature rabbits that are overweight or loose-skinned. The hairless pouches that contain the scent glands, on either side of the genital open-ing, can also become infected. Affected rabbits have soiled fur under the tail and around the genitalia, which may smell strongly. There may be purulent material within the skin folds that can be mistaken for a vaginal discharge. The most effective treat-ment is to remove the skin folds, which is described in Chapter 21.
Behavioural changes, such as aggression Rabbits that are pregnant, pseudopregnant or have adrenal disease (see Chapter 20) can become in-creasingly aggressive towards their owners or other rabbits.
Mammary development, cysts or neoplasia Abnormalities of the mammary tissue often co-exist with uterine disease. Mammary development is a feature of pregnancy, pseudopregnancy or ovarian disease. Marked mammary development can also be associated with neoplasia and may be a sign of pituitary adenoma (Sikoski et al., 2008). Malignant mammary tumours, notably adenocarcinomas, can occur. Metastasis to the lung may take place.
Surgical technique for neutering female rabbits
The technique for ovariohysterectomy is described in Operative Technique 12.1.
Considerations for ovariohysterectomy
• Rabbits are prone to uterine tumours, so it is advisable to remove the uterus, especially in animals over a year old. However, the risk of uterine disease is greatly diminished by removing the ovaries, so ovariectomy may be sufficient to prevent uterine disease if the procedure is performed before the rabbit is old enough (<1 year) to develop reproductive tract problems.
• Spaying sexually immature females is more difficult than spaying mature females because the immature uterus is small, thin and friable (see Figure 12.1).
• Rabbit blood clots quickly but the blood vessels that supply the ovaries and uterus are so large that they need to be tied off in the mesovarium and mesometrium.
The uterus of a French Lop rabbit that was presented for neutering. The uterus was filled with fluid hydrometra . rior to surgery the rabbit weighed 4.5 kg; following surgery she weighed 3.4 kg. The rabbit was thin with a distended abdomen and no body fat despite eating well. She made a full recovery following ovariohysterectomy.
12.7
Extrauterine pregnancy
Extrauterine pregnancy is relatively common in domestic rabbits (Bergdall and Dysko, 1994). It is due to the escape of a fertilized ovum into the abdominal cavity or the rupture of a pregnant uterus (Harper and Ensley, 1982). Implantation usually occurs on the parietal peritoneum. The fetus becomes mummified and is palpated as an abdominal mass. Radiology or ultrasonography can be used in the differential diag-nosis of this condition or it may be discovered during ovariohysterectomy (Figure 12.8).
• Rabbits have two uterine horns and two adjoined cervices. As in other species, the cervix acts as a seal and a barrier against infection and/or urine entering the uterus.
• The vagina is a long, friable, flaccid structure, which fills with urine during urination.
• In rabbits, if the cervices are removed, there is a risk of urine leaking into the abdomen unless the vaginal stump is effectively repaired or ligated.
There is pressure on the ligature or vaginal suture line during urination.
• Ligating the vagina without leaving an area of devitalized tissue is difficult. If excess tissue is removed, the vagina easily slips out of the ligature unless a transfixing suture is used.
• The uterine artery is closely attached to the wall of the cervices and vagina. A transfixing suture can easily penetrate the uterine artery.
• The friable nature of the vaginal tissue can make oversewing difficult as the suture material can tear through the tissue.
• Rabbits are prone to fat necrosis in areas of the mesometrium that have been devitalized by ligation.
• Adhesions and granulomas form readily around any area of devitalized or traumatized tissue.
These can cause problems, especially around the cervical or vaginal stump, which are
anatomically close to the ureters, the rectum and the bladder (see Figure 12.2).
• Many of the problems associated with
ovariohysterectomy can be avoided by ligating the cervices rather than the vagina. Each horn is ligated separately before encompassing and ligating the double cervix (see Operative Technique 12.1). The advantages of this technique are:
It is quick and simple
The ligature sits securely in the cervical tissue, which is much firmer than the flaccid vaginal tissue
The residual cervical tissue is an effective seal against infection or urine entering the abdomen from the vaginal stump
No transfixing suture is required so there is no risk of haemorrhage
The ligature is not close to the ureters, bladder, rectum or blood supply to the bladder.
• The only disadvantage of ligating the cervices is that a tiny amount of uterine tissue is left behind, but this is not significant unless the tissue is neoplastic or abnormal.
• Wound interference can be a postoperative complication after ovariohysterectomy.
Subcuticular sutures and a comfortable wound repair help to prevent it (see Chapter 11). Other measures to prevent wound interference are described in Chapter 2.
• Rabbits are prone to gut stasis following any stressful event. Surgery and pain are stressful and ovariohysterectomy can trigger gut stasis.
Good postoperative care, effective analgesia and careful observation by owners are essential (see Chapter 2).
Potential complications of ovariohysterectomy
Haemorrhage
Transfixing the cervices can result in haemorrhage into the abdomen and/or vagina from the uterine artery, which is closely attached to the wall of the cervices. Rabbit blood clots quickly so the haemor-rhage is seldom a problem but can be avoided by tying off the uterine horns (see Operative Technique 12.1) rather than using a transfixing suture that can easily penetrate the uterine artery.
Transection of the vagina, resulting in urine leakage into the abdomen
The vagina is a flaccid structure that fills with urine during urination. If it is transected below the cervices and ligated or oversewn, pressure is applied to the ligature or suture line during urination and there is a risk of leakage. If this occurs, a local peritonitis can result, which may be life-threatening or may cause adhesions and tissue reactions involving the ureters, bladder or rectum, all of which are anatomically close to the vagina (see Chapter 13). These compli-cations can be avoided by tying off the uterine horns at the cervix rather than transecting the vagina (see Operative Technique 12.1). The ligature is secure and the cervical stump is sealed.
Granulomas and adhesion formation
Any area of devitalized tissue can become necrotic.
These areas can cause problems around the cervi-cal or vaginal stump if they are close enough to occlude a ureter. Hydronephrosis can be the result.
Granulomas can cause urinary incontinence from pressure on the bladder, especially if the vaginal stump is adherent to it. They can also adhere to the rectum and cause stricture. These complications can be reduced by ligating the mesometrium around the cervices rather than around the vagina.
Fat necrosis
Some fat necrosis is unavoidable around ligatures in the mesometrium of obese rabbits. The fat decom-poses into fatty acids and glycerol. With time, these areas of fat necrosis can calcify as calcium binds with the fatty acids. Areas of fat necrosis in the mesometrial remnants seldom cause problems but may be obvious on abdominal radiographs (Figure 12.9). If infection is present, these areas can become abscesses that spread along the lymphat-ics or into the omentum. The risk of fat necrosis is reduced by using fine suture material (1.5 metric, 4/0 USP) and avoiding catgut.
Wound interference
The occasional rabbit will interfere with its abdomi-nal wound, no matter how comfortably repaired it was or how much analgesia is used. Thin, healthy, lively young rabbits (especially wild rabbits) are most likely to remove their sutures. Elizabethan collars are not recommended as they are stressful and can therefore cause anorexia and gut stasis. An effective, temporary method of preventing a rabbit