Rabbit Reproduction - Anatomy & Physiology
Male
The male rabbit is known as the buck.
Penis
The penis has a rounded penile sheath and urethra. It can be easily extruded in rabbits over 2 months of age.
Testes
The rabbit has two testes that descend at approximately 12 weeks of age. These testes are large with epididymal fat pads. In the adult male they lie in two almost hairless scrotal sacs which are cranial to the penis (in the majority of placental mammals they lie caudal to the penis). The inguinal canal remains open throughout life.
Accessory Sex Glands
The seminal vesicles open into the prostatic section of the urethra. The bulbourethral glands are small and paired. They form a bilobed swelling in the dorsal wall of the urethra, just behind the prostate.
Mammary Gland
Male rabbits do not possess nipples.
Female
The female rabbit is known as the doe.
Uterus
The female rabbit has a bicornuate duplex uterus. This has two separate uterine horns and no uterine body. Each horn has its own cervix, and the two cervices open into a single vagina.
The mesometrium is a major fat storage organ. It is very friable and contains many vessels, however only minor anastomoses exist between the uterine and ovarian vasculature.
Puberty and Sexual Maturity
The age of sexual maturity varies with breed:
- Small breeds mature at ~5 months
- Larger breeds mature as late at as 8 months.
Breeding Characteristics
Rabbits are induced ovulators with no well-defined oestrous cycle. The female rabbits have periods of sexual receptivity every 4-6 days and the oestrus period lasts ~14 days. Ovulation occurs within 10 hours of coitus.
The breeding season lasts from January to October in the UK.
Does can become quite territorial and this needs to be taken into account when planning any matings. It is advisable to take the doe to the buck rather than the other way round.
Gestation and Offspring
Pregnancy diagnosis
Foetuses may be felt by gentle abdominal palpation as early as 10 days post breeding as 1 to 1.5cm masses in the caudal ventral abdomen. At 18 days they should be 2.5 to 3cm in length.
Radiography or ultrasonography can be used after 21 days if necessary.
Gestation
The gestation period of a rabbit is 29-35 days.
Pseudopregnancy may occur, which lasts approximately 18 days. It can be caused by infertile mating, or the presence of a male nearby. The dam is unable to conceive during this time. During pseudopregnancy, the corpus luteum secretes progesterone, which causes the uterus and mammary glands to grow.
Litter
The litter size can vary from 4-12 offspring.
The young are altricial - born hairless, deaf and blind. Offspring are totally dependent on their mother for the first few weeks of life. They are protected from the environment and predators by the nest which is made by the doe using hair from her dewlap. If the nest is disturbed, the doe may cannibalise the offspring.
Mammary Gland and Lactation
The doe has four or five pairs of nipples. The mammary gland develops in the last week of pregnancy. Suckling is stimulated by a pheromone produced by a gland near the nipple.
Consumption of water and caecotrophs by the doe increases 10-fold during lactation.
Rabbit milk is richer than cow's milk, it has an unusually low lactose content and a very high protein and fat content.
Composition:
- 13% Protein
- 9% Fat
- 1% Lactose
- 2.3% minerals
Sexing
Kits are best sexed at birth or at weaning (5-8 weeks of age). In between those times it can be difficult to exteriorise the genitalia.
Sexing is performed by gentle pressure on the genital orifice which everts the penis or vulva. The male has a cylindrical organ with a rounded to oval-shaped urethral opening. The female vulva has a leaf-like appearance with a slit-like opening.
In the male the testicles descend at around 12-14 weeks of age and can be palpated, although they can be retracted into the abdomen if the rabbit is stressed.
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References
Richardson, V. (2000) Rabbits Health, Husbandry and Diseases, Blackwell Science