Immunocontraception is a technique that uses the body's own immune system to prevent pregnancy.

"For almost four decades we have known that antibodies against the membrane of a mammal's unfertilized egg can be used to inhibit fertility," explained Jay F. Kirkpatrick, PhD, director of the science and conservation center at ZooMontana, located in Billings, Mont.

Kirkpatrick said these antibodies–produced in response to a group of proteins derived from the membrane surrounding pig eggs–will block fertilization. The proteins can be administered to a variety of mammals like a vaccination to control reproductive rates.

Because some mammals pose significant population problems, researchers evaluated the use of a porcine zona pellucida (PZP) vaccine to control wildlife populations