Mice are vasectomized to be mated to females used for embryo transfer. The female becomes pseudopregnant, her body geared for a pregnancy because she has been mated. Vasectomy is performed on mice at 6-8 weeks of age. I routinely use the Swiss Webster or CD1 outbred strains, although past usage includes both C57Bl/6 and B6C3F1.

The Anesthetic

Avertin (2,2,2 tribromoethanol) is found to be quite effective. For method of preparation, see "Manipulating the Mouse Embryo", CSHL Press, ISBN 0-87969-384-3. Store wrapped in tin foil at 4oC as this reagent is light sensitive. Test after making a new batch. Shake well before use. Anesthetise mouse with Avertin, administered intraperitoneally. After administering the anesthetic, put the mouse back into the cage from which it came. The mouse will be more relaxed when placed in a familiar environment and the anesthetic will act more quickly than it would on a distressed mouse.

To check that the mouse is fully anesthetised, press or squeeze the pads of the feet. If the mouse can feel this it will try to withdraw its leg from your grasp (Pedal reflex). Do not commence surgery until there is no reflex reaction to this test. We do not use mice which weigh less than 25grams.

Procedure

The mouse is weighed and anesthetized accordingly. Lie the mouse on its back and swab the intended incision site with 70% EtOH. Using a pair of curved forceps and Surecut scissors, cut across the lower abdomen approximately 0.5 inch anterior to the genitals, making the incision about one cm wide. Wipe the incision site with a lint-free tissue dampened with 70% EtOH to remove excess cut hair. Incise the body wall, reach in and locate the bladder. Both tubes of the vas deferens will be visible lying on either side.

Grasp the left vas deferens gently with forceps and lift a section clear of the incision. Tuck the curved forceps underneath the vas deferens and allow them to spread to their natural unsprung state, with the ends pointing vertically. While in this position, use the suture to make two firm knots in the vas deferens, about 4-5 mm apart, tying both knots firmly. Cut out a section of vas deferens from in between the knots and place on a tissue to be sure that one side has been done.

Gently ease the two cut ends of the vas deferens back inside the abdominal cavity and repeat procedure on the right hand side. When both sides have been done, sew up the incision in the body wall with separate stitches - two or three should suffice. The suture should be kept in the EtOH in the petri dish when not being used - this keeps the silk from drying and sticking to tissue and fat when another suture is required.

The skin is closed up using two to three Autoclips to hold the wound closed. The mouse should be wrapped in a tissue to keep it warm (loss of body heat is common in abdominal surgery) or alternatively placed on a heat pad, and allowed to recover. Animals which are placed under anesthetic should always be supervised and monitored until fully awake.

Following the operation, the mice are allowed to recover for two weeks before being test bred to confirm their sterility.

Test Breeding

One or two female mice are placed with the vasectomized male and are checked for plugs the following morning. Females which plug are sacrificed and their oviducts flushed 24 hours later with PBS. The eggs should be at one cell stage or unfertilized. If they are at two cell stage then the vasectomy was not performed correctly and the male should be culled.