PZP is a vaccine derived from slaughterhouse pig ovaries (yes, we’d prefer this wasn’t the case). When injected into a female mammal this foreign protein induces an immune response that results in the generation of antibodies to combat the protein. Some of these antibodies attach to the sperm receptors on the zona pellucida of the target animal’s eggs and thereby prevent fertilization.
For more detailed information, you should visit these sites:
ZonaStat-H – The Science and Conservation Center manufactures ZonaStat-H, otherwise known as “native PZP.” It is the product we use to treat the Onaqui Mountain Herd.
PZP-22 – Is comprised of a combination of native PZP and PZP that is incorporated into lactide-glycolide pellets that are designed to dissolve in the host’s body slowly over time. It contains both a primer and booster dose. The hope was that it would provide at least 22 months (hence, it’s name) of pregnancy prevention with a single injection, but the results have been more on par with native PZP.
Dr. Jay Kirkpatrick (deceased) was the head of The Science and Conservation Center and was an authority on the manufacture and use of PZP to control wild horse populations, as well as other wild animals. He performed a lot of research by treating the horses of Assateague Island with PZP.
We typically deliver primers in the Fall, then go back and dart with boosters in the early Spring.
A number of the mares of the Onaqui were treated with PZP-22 and released during prior round-ups. They are marked with the BLM neck freeze brand, and a hip brand. They only require boosters each year.
The brands on this mare indicate she was treated with PZP-22 in 2012 and released. She was gathered as part of an operation where other horses were removed from the range. The picture was taken in 2016, so it is obvious that her fertility treatment wore off.
Here are pictures of the dart and delivery devices we typically use:
Note: We do not typically use darts with gelatin collars, which
is the green piece on the needle of the dart in this picture.
To the cost of the dose you need to add the costs of delivery. This varies greatly by method:
Dose by darting in the field: This requires purchase of the PZP and a dart (about $30 combined), plus the time and expenses for the darter. When the BLM uses volunteers, such as our organization, it doesn’t incur additional costs (but we do). When a BLM employee darts a horse, the darters time and costs (vehicle, etc.) should be calculated into the total cost per dose.
Dose when gathered and released: Sometimes, during a gather and removal operation, some mares are treated with PZP and released. Typically, they are treated with PZP-22 (about $300) and released. The cost of this type of treatment is mostly just the cost of the dose, since the gather and removal is the main focus of the operation.
Dose when gathered and held, then treated again, and released: Lately, we’ve been hearing that it costs $2,600 to treat a horse with PZP. This figure is a bit misleading, and is sometimes taken to mean the cost of delivering a dose in the field by dart gun. This is not accurate. The $2,600 figure comes from when the BLM gathers a wild horse by helicopter, transfers it to a holding pen, injects a primer dose of PZP, holds and feeds the horse for 2-4 weeks, delivers a booster dose of PZP, then releases the horse back to the range.
Dose by bait/water trap: This is when a wild horse is trapped in a pen and a dose of PZP is delivered. This is, so far, a fairly infrequent scenario, and we don’t know the costs. However, we’d like to see it more frequently applied.
With that said, there are many groups (such as ours), who are willing to try to dart the more wily horses. Ghillie suits, bait/water trapping, and other methods are part of our plans.
Mostly, we just need a big “go-ahead” from the BLM.
The one thing we will address, on this front, is the topic of how PZP is registered with the EPA.
IT’S A PESTICIDE! PZP is registered with the Environmental Protection Agency (EPA) as a pesticide, as are other wildlife contraceptives. Despite knowing this fact, there are anti-PZP groups and advocates who feel the need to repeatedly point out that the horses are being treated with a “PESTICIDE!” (Oh, the humanity…) While this may resonate with those unwilling to actually look into the subject, those of us in the know just sit back and roll our eyes at this juvenile argument that does nothing beyond creating unnecessary divide among horse advocates who want to help the animals. Trust us, we are not out spraying the wild horses with Raid Roach Killer…
Here’s a link to the EPA’s PZP Pesticide Fact Sheet