Female reproductive tract and ovariohysterectomy
Esther van Praag, Ph.D.
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WARNING: this file contains pictures of the surgical procedure that may be distressing for people.
The reproductive organ of the female rabbit is considered primitive. Indeed, the split two-horned system is only encountered in monotreme egg laying mammals and the lagomorphs (pika, hare and rabbit). The organ is held in place by a broad ligament that is anchored at 4 points under the vertebral column.
Sex differentiation occurs during the embryonic phase, on the 16th day post-fertilization. The ovaries grow from an aggregate of cells that is lying near the original testes. The development of the ovaries is accompanied by the degeneration of the testes.
The development of the ovules (female reproductive cell) starts around the 21st day and continues till birth, around the 30th day. The first ova and follicles start to develop only 13 days after birth.
The reproductive organ of the female rabbit is duplex: the uterus is formed by two independent horns, split over their whole length (± 7 cm). Each horn possesses its own cervix. The ovaries, ellipsoid bodies that have a maximal length of 1-1.5 cm, are located at the end of the uterus, right under the kidneys. They are hidden by the mesometrium (portion of the broad ligament that separates and encloses the uterus) and fat.
The vagina does not present any particularities. This part of the reproductive tract is large, with the urethra joining halfway, at the level of the vaginal vestibule. At the end of the vagina, the glands of Bartholin and preputial glands can be recognized.
The age at which sexual maturity is reached depends on the size and the breed: while small and middle sized rabbits become adult between 4 and 6 months, it may take between 5 to 8 months for giant breeds. As a rule, it is considered that a rabbit is adult and able to reproduce when it has reached 75 to 80% of its adult size.
Female rabbits do not have an estrus (heat) cycle, as do other small animals like dogs or cats, but are called induced ovulators. Ovulation is spontaneous; it happens 9 to 13 h. after copulation.
A certain cycle does nevertheless exist. The presence of the estrogen hormone will influence the size and the color of the vulva. Most female rabbits are more prone to mate when their vulva is colored reddish/purple. It is no clear indication though, as some female rabbits, called “reflex ovulators”, will mate when their vulva is pale and small.
The spay of female rabbits is recommended in order to avoid unwanted litters, pseudo-pregnancies and reduce difficult behavior, like the marking of its territory with strong smelling urine, aggressive attitude and mounting of objects or human body parts like feet and arms. Further medical reasons to favor of a spay surgery include:
• Difficult to treat bacterial infection or pyometra;
• Neoplasia of the ovaries or uterus (e.g. adenocarcinoma), a problem frequently seen in unspayed older rabbits;
• Abnormal swelling of the wall of the uterine artery (uterine aneurysm).
Ovariohysterectomy is a surgical procedure done under general anesthesia, in a sterile environment, with sterile surgical instruments and a preparation of the skin. Indeed, any post-surgical infection becomes a medical emergency.
A spay is usually done around the age of 5 months, or when the rabbit is sexually mature. At a younger age, the surgery is complicated by the difficulty to locate the very thin uterus and the very small ovaries. A spay at immature age may also have a dramatic effect on the proper calcium absorption by the bones.
When a spay surgery is done in an older rabbit, it is advisable to do an ultrasound prior to surgery in order to rule out the presence of tumors, and, if found, to check for the presence of metastasis (e.g. in the lungs) before the surgery.
Various surgical approaches are available for ovariohysterectomy in rabbits, described in books, videos, or scientific articles.
Video and step by step illustration of a spay surgery in a female rabbit
Post surgical care
The administration of pain medication for several days after the surgery is highly recommended. Pain indeed induces hormonal and physiological responses, which slow down the activity of the digestive tract, delay food intake and recovery.
The presence of blood in the urine during 24 to 48 hrs. post-surgery is sometimes observed.
Rabbits have a propensity to form intra-abdominal adhesion post-operatively. These complications can be reduced by the administration of verapamil (200 μg/kg, SC, tid for 3 days). Studies showed that the NSAID pain drug ibuprofen has the same preventive effect against adhesion as verapamil.
The rabbit should furthermore be confined for 7 to 10 days, and kept separated from other rabbits up to 10 days post-surgery.
Healthy and diseased female reproductive organs
Many thanks to Akira Yamanouchi, for the permission to use pictures from VEIN (Veterinary Exotic Information Network, http://vein.ne.jp/).
Many thanks also to Debbie Hanson (USA) for the spay videos. a
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