January 11, 2010 – Introduction to PZP

It is becoming more and more common to hear about wild horse populations managed through fertility control, especially fertility control with the immunocontraceptive Porcine Zona Pellucida (PZP). This is a complex topic, but I feel it is well worth understanding. In the days to come, I will be discussing major points relating to PZP that I think are important to understand. Today, I would like to start with an interesting story that helps set the stage for future posts.

The Pryor Mountain Wild Horse Range was established in 1968, and so people working there, like Ron Hall and Lynne Taylor, were able to develop an understanding of wild horse management by the time Congress passed the Wild Free-Roaming Horses and Burros Act in 1971. Shortly after the 1971 Act was passed, Hall and Taylor came to visit with Dr. Jay Kirkpatrick, who at the time was an assistant professor at Montana State University. Dr. Kirkpatrick tells of how he had a knock at his door and found two cowboys standing there. These two had on their cowboy hats, boots, and everything else. Hall and Taylor explained how they were pleased to see the 1971 Act provide protection to all wild horses, but they were concerned with the future of managing wild horse populations. The 1971 Act provided direction in the protection and management of wild horses, but it didn’t really explain how to effectively do this. They asked a question that had never really been asked before: Can you make horses stop reproducing?

Dr. Kirkpatrick figured that if human reproduction could be stopped, then surely the same could be done with wild horses. He became interested in this topic, and he soon began to research how it could be done. This was a new field; wildlife contraception was something that hadn’t yet been well researched. The first attempts at using fertility control to manage wild horse populations were done through the 1970’s into the early 1980’s. The contraceptives used then were similar to the birth control used by humans. They worked, but they were not practical for use in managing wild populations. In the late 1980’s, Dr. Kirkpatrick focused his attention on a totally different type of contraceptive, an immunocontraceptive called PZP, that was being tested on domestic mares by researchers at the University of California, Davis. It was from this that the idea of using PZP to manage wild horse populations originated.

I always find it interesting to know that the Pryor Mountain Wild Horse Range influenced the science of wildlife contraception. I was very happy to see this story written about in the September 18, 2009 edition of Science. (It’s on page 1491 in the article entitled “A Cure For Euthanasia?”.) Something I want to emphasize with the above story is that a lot of research has been done on fertility control for wild horses. This started with Dr. Kirkpatrick’s early research in finding a suitable contraceptive, and it is still a topic that is researched today. Because of this, we can look to this research to seek the answers to our questions on PZP. With that, here is the tentative schedule of topics that I will be posting in the coming days:

  • 1/12/10: How does PZP work? (part 1, mammalian reproduction)
  • 1/13/10: How does PZP work? (part 2, PZP’s function)
  • 1/14/10: How is PZP made? Who makes it?
  • 1/15/10: How is PZP distributed, and what is the planning process for its use on wild horses?
  • 1/16/10: How is PZP administered?
  • 1/17/10: What are the physiologic effects of PZP?
  • 1/18/10: What are the behavioral effects of PZP?
  • 1/19/10: What are common misconceptions about what PZP can and can’t do?
  • 1/20/10: Where is PZP used, part 1: Assateague Island
  • 1/21/10: Where is PZP used, part 2: The Pryor Mountain Wild Horse Range
  • 1/22/10: Where is PZP used, part 3: Other wild horse herds
  • 1/23/10: What other animals have been treated with PZP?
  • 1/24/10: What other types of fertility control are there?
  • 1/25/10: Who supports PZP?

Again, I feel that the above topics are very important to understand; and I would really encourage any questions that may arise. There’s no reason to be confused on what PZP is and what it is not as we have a great body of research to draw upon in developing understanding. I look forward to going through these topics in the days to come, and I am also hoping to eventually put together similar posts on managing wild horse populations through predation and removals.

Published in: on January 11, 2010 at 5:24 pm  Comments (10)  

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10 CommentsLeave a comment

  1. Matt, thank you for this post and the upcoming ones as well,

    • Thank you too for your support!

  2. Matt,
    Fantastic! I’m really looking forward to these posts. It has been on my mind since I started reading about the wild horses and what to do with their numbers increasing and their habitat shrinking.
    Thank you.

    • Thanks for your support! I hope you are able to get a lot out of these posts.

      • Matt,

        Are Hall and Taylor still alive?


      • Lynne sadly died a few years ago. I really wish I could have gotten to know him, he did some great work in the Pryors.

  3. Looking forward to the series, Matt. One question so far. Who were Hall and Taylor working for back then, and in what capacity?

    The story of the Pryor Mountain Wild Horse Range is getting more fascinating every day.

    Thank you so much.


    • They worked for the BLM and were working with the horses a lot. It was their early work and notes that has allowed us to have such a surprisingly good understanding of the horses and range back in those days.

  4. I think this series will be very informative and help to dispel some of the questions that folks might have after hearing about PZP on other web sites. Is PZP still considered “experimental?” What role does the USHS play in administration of PZP? Is it true that PZP can cause mares to foal late in the season?

    Thank you for your efforts in educating us about this and other topics related to managing wild horses. It is interesting that population increases are an unintended consequence of the 1971 law, and that BLM is provided little legislative direction other than to remove excess horses.

    • Whether or not PZP is currently considered experimental depends on perspective, I guess. The current and future status of this will be something I definitely elaborate on in one of these early posts. The Humane Society’s involvement with PZP will also be something we touch on. The out of season foaling issue will definitely be a big one to address; this will be coming toward the middle with the information I’ve been given and have found on my own about it.
      I look forward to getting some of these more exciting posts composed in the days to come.

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