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CLINICAL TECHNIQUES
Cyndi Brown, DVM, Column Editor
Intra-abdominal castration in the rat
Normal rat posture results in proximity of the scrotum to bedding and feces, which predisposes rats to postoperative complications if castration is done using standard scrotal and prescrotal approaches. This column describes a ventral abdominal approach for castration in the rat.
Reasons for neutering rats are similar to those for neutering dogs or cats. Neutering prevents unwanted pregnancies; permits both sexes to be housed together; reduces or abolishes male aggression, which minimizes fighting and bite wounds; modifies scent-marking behavior such as spraying urine or depositing feces; and prevents testicular cancer. Castration modifies sexual behavior in rodents but may not abolish it altogether. Aggressive behavior towards handlers can be modified by neutering, especially if this behavior is hormone-related. Copulatory actions may continue after neutering as a part of dominance or excitement behavior. The male should not be considered sterile until at least 4 weeks after castration.
Background
Testicles descend into the scrotal sacs at 34 weeks of age in rats. Although rats can be castrated at any age, approximately 1220 weeks of age is the best time. In the male rat, a few sperm can be ejaculated at 7 weeks of age but full reproductive capacity is not reached until 10 weeks of age. Rats are able to retract their testicles from within the scrotum through the inguinal ring, which remains open throughout life. This response can be evoked by handling of the testicle, even under light anesthesia.
There are several methods of castration. The best choice depends on the preference of the surgeon and the circumstances of the rat. In most cases, scrotal castration (incision through skin at the tip of the scrotum) is described13 but a prescrotal approach can be used as well. When these approaches are used, the technique can be an open or closed castration. Open castration refers to incision of the spermatic fascia as well as the parietal vaginal tunic to expose the testicle proper. Closed castration refers to ligature
of the entire spermatic cord and tunics to remove the testicle. A closed technique makes it impossible for viscera to herniate into the scrotum because the tunic is tied off. Most rodents have large fat bodies in the...