PZP is the abbreviation for Porcine Zona Pellucida. The zona pellucida is "The strong membrane that forms around an ovum as it develops in the ovary. The membrane remains in place during the egg's travels through the Fallopian tube. To fertilize the egg, a sperm must penetrate the thinning zona pellucida. If fertilization takes place, the membrane disappears to permit implantation in the uterus" (http://www.medterms.com/script/main/art.asp?articlekey=11822). The "porcine" refers to the origin of PZP: from slaughtered pigs. This membrane is prepared as an injection for a number of mammalian species, and the animal injected then produces antibodies for these proteins. Since this protein membrane is critical in allowing sperm to travel inside the ovum (egg), the antibodies effectively stop fertilization.

The first report on the use of PZP in feral and domestic animals (horses) was in 1989 (Liu, Bernoco and Feldman, Journal of Reproduction and Fertility 85:19-29). Since then, there have been a number of wildlife species in which this vaccine has been successfully used. Among the animal species in which experimental projects have been scientifically documented are wild horses in Nevada (Turner, Liu and Kirkpatrick), the white-tailed deer in Ohio (Turner, Liu and Kirkpatrick), the American black bear in South Dakota (Lane and Liu), the tule elk in California (Stoops and Shideler), the South African elephant (Fayrer-Hoskens and Bertschinger), and llamas and alpacas in Peru (van Leeuwen and Liu). The procedure for the production of PZP was developed by UC Davis researcher Dr. Jerry Hedrick and applied to domestic and feral animals by Dr. Irwin Liu. Since 1987 these researchers have provided considerable quantities of PZP to various governmental and private agencies throughout the world for the experimental purposes of contracepting and humanely controlling animal overpopulations where applicable. The agencies that were provided with the PZP vaccine include: the Humane Society of the United States; the Science and Conservation Center; Bureau of Land Management, Dept. of Interior; Santa Cruz Island Foundation; National Park Services, Dept. of Interior; the National Zoological Research Institute, Italy; University of Madrid, Spain; University San Marcos, Peru; the Institute of Zoology, Beijing, China; and the National Wildlife Research Center, USDA-APHIS, Colorado. The UC Davis researchers are continuing to perform collaborative research with these and many other agencies and nonprofit organizations not mentioned above. While the UC Davis researchers are not commercially marketing the PZP, they hope to generate funds for continuing research in PZP through marginal, laboratory replacement and personnel costs for the production of PZP. The UC Davis researchers are continuing to develop PZP and hormone-based agents aimed at effective and humane methods for contraception and sterilization of animals. These methods are being developed to serve as alternatives to current methods of controlling overpopulation of domestic and wildlife animals. You might contact Dr. Liu for more information on the use of PZP and its availability: Irwin KM Liu, DVM, Ph.D., Department of Population Health and Reproduction, 1114 Tupper Hall, University of California, Davis, CA 95616. Email: ikliu@ucdavis.edu or Fax: (530) 752-1358.