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This procedure may be used to derive a strain of pathogen free mice from a strain with an infection problem or one of unknown health status. It may be necessary to perform the procedure inside an isolator. All operating instruments (two pairs of scissors, one pair of surgical forceps) need to be sterile. The second pair of scissors are used for cutting through the uterine wall to avoid cross-contamination from the skin of the mother to the sterile uterus and pups.

The pregnant mother is killed by cervical dislocation. Drugs must not be used as this will affect the pups.

The mother is dipped in disinfectant before commencing the operation. The disinfectant used here was a dilute iodine solution.

Excess disinfectant is removed with sterile tissue.

The mother is secured to the operating area inside a hood.

The animal is covered with sterile drape.

The skin with the drape attached is lifted with a pair of surgical forceps and a midline incision is made through both drape and skin, using sterile scissors. The skin incision should reach from the xiphoid area to the inguinal area. The muscular layer is then lifted and cut through in the same manner. The abdominal wall is lifted away from the abdominal organs during the incision to avoid damage to the uterus.

Using gentle pressure the gravid uterus is expressed from the abdomen on to the sterile drape. The fingers are used here because sharp instruments can unintentionally harm the pups or placentae or cause the uterine wall to rupture.

The gravid uterus is removed by cutting through the fallopian tubes and the vagina. The second pair of scissors are used from this point.

The entire gravid uterus is placed into a pot of warm disinfectant.

After one minute the uterus is tipped into a sterile container.

The uterus is removed from the container.

A cut is made in the major curvature of the uterine wall taking care not to harm the pups with the scissors as the uterine wall is extremely thin. The uterine wall and fetal membranes are dissected away to reveal the pups.

The pups are left attached to their placentae and the nasal area is wiped carefully with sterile tissue to remove amnionic fluid and to stimulate breathing. It may be beneficial to massage the thorax of the pups carefully for further stimulation of breathing. It is important that the pups do not get cold during this procedure. Pups with poor breathing may be stimulated with doxapram given as a sublingual drop of minimal size.

When breathing has been established the umbilical cord is clamped and then cut.

Healthy pups are transferred to a foster mother of known health status.

A description of cross-fostering technique in the rat is available here.

This presentation is one of the 3500 audiovisual aids cited in the NORINA database.

The Unit is gradually building up a list of teaching materials, that may be viewed here.

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