. Porcine Zona Pellucida, or PZP has been used for many years as a contraceptive for Wildlife. It is a vaccine that is given by an injection into a muscle of the female. PZP blocks fertilization. PZP creates antibodies that attack the zona pelcida membrane that surrounds the egg. The antibodies deform the membrane to prevent the sperm from attaching to the egg.
The Wildlife Fertility Control, The Cutting Edge of Science states “Thus far PZP has been a promising form of contraception in wildlife because
1. it has prevented pregnancy an average of 90% of the time in treated animals
2. it can be delivered remotely by small darts
3. the contraceptive effects are reversible
4. it is effective across many species
5. there are no debilitating health side-effects even after long-term use
6. it has almost no effects on social behaviors
7. the vaccine cannot pass through the food chain
8. it is safe to give to pregnant animals (see Kirkpatrick et al. 1996b).”
Whether PZP-22 is widely adopted, says Guilfoyle, will depend on the decisions of individual managers, such as Warr and Jerome Fox. Fox, the wild horse and burro specialist at Sand Wash Basin, says he knows his BLM colleagues are closely following the trials. “There’s a lot of attention being paid to what’s happening at Sand Wash and Cedar Mountains,” he says. “Favorable results or negative results are going to have a huge impact on the horse program.”
In Sand Wash Basin the, Sand Wash Advocate Team, (SWAT), and other BLM volunteers dart with PZP for herd population control.
I spent a day in the Basin with a dart team to better understand the process, and applaud all the darters for their time and commitment to this project. They hike miles, in hot sticky weather, carry the heavy dart guns, watching for gopher holes and the ever present hidden rattle snakes, all the while watching the wild mare they are trying to dart.
Here’s a short summary of what I learned and what the process involves. Probably the most important piece of the darting program is the identification of the mare and the record keeping that follows, after the mare has been darted. Before you can actually, head out to dart, you have to check their records to see who needs to be darted or who has already been darted. They also have to prepare both boosters and primers. My understanding is that the first year the mare needs a booster then later that year or the next year and the following years she will just need a booster. The PZP has to be kept cold for the entire time.
The first thing that happens once you are on the range is locating the targeted mare. There are 160,000 acres in Sand Wash Basin for the mare to be hiding in. Early in the year almost every band of wild horses that you see will have a mare in it that should be darted. As more mares are darted finding the right mare to dart can take a lot longer, as the selection of un-darted mares decreases. Once you have found the mare that needs darted, you have to determine if she needs a booster or a primer, load the darting gun and try to get as close to her as possible without spooking the band or her. The darter needs to determine the best angle, account for the wind direction and aim for her hip. A second set of eyes is very beneficial, that person can track the dart once it has hit the mare and popped out. After the targeted mare has been darted the dart is then retrieved to make sure that the PZP injected into the mare. Finding the dart can be a long process. Some mares will spook and move to a different location before the dart falls out, others lose it almost immediately. After collecting the dart then the paper work needs to be completed so the next person that goes to the Basin to dart will have records of who was darted and when.
It’s a lengthy process. The expected coverage of the PZP is one year, and mares carry a foal for 330-345 days. If the mare is already in-foal when she is darted you have a window after she foals to dart her again before the PZP wears off. The challenge is can she be found and darted before she is bred again.