Congenital anomaly in male rabbits:
split penis or hypospadias
Esther van Praag, Ph.D.
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Hypospadias is a congenital anomaly of the penis that is observed relatively frequently in men. It also affects animals and has been observed in all breeds of rabbits. The closure of the penis is incomplete. This is due to the incomplete development of penile tissue that forms the anterior urethra (spongy urethra), the canal through which urine is discharged from the bladder to the outside during voiding. As a consequence, the external orifice of the urethra (urinary meatus) is found on the underside of the penis, with an opening located more or less close to the tip of the penis (gland), or as a split. The foreskin is usually underdeveloped et found only on the upper side and on the sides of the penis head.
The anomaly is classified from light to severe and may be accompanied by an abnormal curvature of the penis.
Etiology of this problem is not well understood. When the problem is regularly observed in a rabbit lineage, a genetic predisposition with autosomal recessive inheritance is suspected. When it appears sporadically, exposure to certain environmental factors that influence the endocrine system and the hormonal secretion is alleged.
The development of the male genital system during the embryonic phase is complex, involving a precise genetic programming, with activation of specific genes that encode for proteins that regulate the production and secretion of testosterone. This phase is accompanied by cell differentiation, enzyme activity et remodeling of tissues. It results in the formation of the penis, penile urethra and foreskin.
When a gene functions improperly or is mutated, or when an exterior factor influences the hormonal secretion, normal development of the mass of spongy tissue surrounding the male urethra within the penis (corpus spongiosum) and of the foreskin is deficient or aborted. As a result, the penis does not completely close on the underside and remains split.
Other than an abnormal looking penis, the male rabbit does not suffer from this condition and may become a perfect house-rabbit. It happens that he will not be able to pee straight, but sideways against the inner side of his hind limbs. This may cause urine burn and loss of fur.
If the deformation is light and located near the tip of the reproducing organ, males may mate and reproduce successfully. The rate of fertility is decreased as produced sperm is spread along the split and not only at the tip. The further the anomaly is located far from the gland, the more the rabbit will be infertile. If this condition is accompanied by a curved penis (chordee), mating is no more possible.
In men, hypospadias may be accompanied by the failure of testicles to descend into the scrotum (cryptorchidism) or by an inguinal hernia in the groin region or in the scrotum. No information is available for rabbits. This hernia forms in the inguinal canal, where the spermatic cord and the testicular blood vessels pass from the abdominal cavity into the scrotum. A muscle weakness within the abdominal tissue leads to the formation of a pocket. A loop of the intestine or the bladder can enter into the pocket in the groin or scrotal regions, respectively.
Many thanks to Michel Gruaz (Switzerland) for the permission to use his pictures.
Baskin LS, Ebbers MB. Hypospadias: anatomy, etiology, and technique. J Pediatr Surg. 2006;41(3):463-72.
Higuchi TT, Palmer JS, Gray LE Jr, Veeramachaneni DN. Effects of dibutyl phthalate in male rabbits following in utero, adolescent, or postpubertal exposure. Toxicol Sci. 2003;72(2):301-13.
Meyer J. Genetische Defekte und züchterische Auslese. KaninchenZeitung. http://www.kaninchenzeitung.de/?redid=352569&seite=0 11.05.2011