This article is a reprint from the Science and Conservation Center
A non-cellular membrane known as the zona pellucida (ZP) surrounds all mammalian eggs. The ZP consists of several glycoproteins (proteins with some carbohydrates attached), one of which, ZP3, is thought to be the primary sperm receptor (the molecule which permits attachments of the sperm to the egg during the process of fertilization). The PZP molecule is derived from pig eggs. When this vaccine is injected into the muscle of the target female animal, it stimulates her immune system to produce antibodies against the vaccine. These antibodies also attach to the sperm receptors on the ZP of her own eggs and distort their shape, thereby blocking fertilization (see Barber et al. 2001; Dunbar et al. 1980; Liu and Shivers 1982; Liu et al. 1989 ; Patterson and Aitkin 1990; Shivers and Liu 1982).
The PZP vaccine must be injected into the muscle of the target animal. This can be accomplished by hand if the animal is restrained, or by dart, for remote delivery (see Kirkpatrick et al. 1990c). There are many commercial dart systems available but the thick viscosity of the vaccine requires a large bore needle and a quick injection. Thus far, the Pneu-Dart® system (Williamsport, PA) works best. The Pneu-Dart® 1.0 cc barbless darts can be fired from any Pneu-Dart® capture gun or from any other brand of capture gun with 13 mm barrels (Pax-Arms® or Dan-Inject®, for instance). The darts are disposable, and after hitting the animal in the rump or hip (the only acceptable sites for administering the vaccine) they inject by means of a small powder charge and pop out. Because of the bright colors the darts are usually retrieved in the field. Undischarged darts cannot be discharged by stepping on them or by any other kinds of casual contact. Over a __ year period on Fire Island National Seashore, and more than ___ dartings of deer, only __ darts have not been recovered.
Normally, each animal is darted twice the first year, with the “primer” inoculation being given up to a year before a booster inoculation. The booster inoculation, ideally, should be given just preceding the breeding season (March for wild horses or September for deer). Thereafter a single annual booster inoculation will maintain contraception, and after the third year, treatment every other or every third year will suffice.
The second inoculation of the first year requires that (1) that you are able to recognize individual animals, or (2) that you administer the first inoculation with a special “marker dart” (also made by Pneu-Dart®) which leaves a dye mark on the animal at the same time it injects the vaccine, or (3) that animals are treated opportunistically and randomly, with the hope of eventually treating a large proportion of the total population over the course of several years.
An alternative strategy is to administer only a single inoculation the first year, from which there will be only limited contraception, and then a single inoculation thereafter, from which there will be significant contraception (see McShea et al. 1977).