Saturday, December 11, 2010

Mustang Contraception:PZP

First of all, thanks to everyone who weighed in yesterday in the Kindle discussion. It did give me the information to ask better questions of the sales rep and make up my mind. We decided to buy one, and we purchased it at Best Buy for the same price it would have been on Amazon. Apparently, it's sold at a number of different stores, Staples, too, which gives you the opportunity to try it out. Kate had a very good discussion about the Kindle on her blog, The Reader's Closet.

Now to the topic I've been working on for today, PZP--the contraceptive used on wild horses.

Everyone who loves Mustangs, despite their views one way or another, can probably agree that the herds, or at least some of the herds, must be reduced in a humane way. The question that always comes to my mind whenever I hear a plan--like the Pickens Plan--is how are you going to control the numbers? (Especially, in a refuge or monument setting where there will be plenty of food and water provided.)

I'm just beginning to study the issue and, at this point, I'm thinking maybe the answer is PZP.

The guidelines the scientific community worked to achieve are that the conceptive should...

-be at least 90% effective.
-be capable of administration by remote delivery.
-either be immediately reversible, or its effects should passively wear off.
-be safe to pregnant animals.
-not pass through the natural food chain.
-be inexpensive.
-have no debilitating side effects on the health of the horses.
-not influence the social behavior of the horses.

I think these guidelines are excellent, and they say they've mostly achieved them in field trials, although I haven't found the evidence from recent studies--the last I found was '02. (See link above) From what I've read, PZP does influence the social behavior of the horses.

Please take a moment to help me, and everyone else who visits the blog, learn more about this subject. What do we know about PZP now? Please share any information you have--links, facts, tidbits, opinions, experience. Every opinion is welcome--I love to hear all sides to a story.

A few great links, in addition to the government link above:

An EXCELLENT article in the New York Times: click here

Article on a negative side-effect, it seems to extend the breeding season. Click here.

Position paper, August 2010, Cloud Foundation. Click here.

Also, if you have a second, please head to Spring Creek Basin Weblog and vote on TJ Holmes' calendar cover. She'll put you in a drawing for one if you do. If I don't win, I'm definitely buying one, or two--they are just gorgeous pictures of Mustangs--each with a wonderful story of its own. She follows this herd's every move and loves them like her own family.

****More links from TJ, who knows more about this subject than I ever dreamed of knowing.****** "The results have been remarkable. On ASIS, the population has dropped from 175 animals to 123 over the 16-year period during the time the vaccine has been used at the management level. Body condition scores of the mares have improved significantly, mortality rates have dropped and longevity has increased by ten years and more, in some cases. The annual cost of the entire program is barely more than the cost of removing four horses through the Adopt-A-Horse program." (this is a video - long - about 90 minutes; it's a presentation Dr. Jay Kirkpatrick made at the Lovell (Wyoming) Community Center last summer)


  1. Comment from TJ Holmes about PZP--excellent information she couldn't get the blog to post. I have to run to our Park Conservation meeting/Christmas party/membership drive--but I'll respond when I get home tonight. I'll post this on a main blog in the upcoming week, too--good information!

    From TJ-
    Thanks for the link, Linda! And I'll round up some links for you about
    PZP. One thing to know is that PZP was created in 1972 and has been used
    for 23 years on Assateague Island horses (95% efficacy rate there as of
    this year) - which are NOT all tame and eating out of tourists' hands.
    :) In fact, the Assateague horses have been called the second hardest to
    dart of anywhere they're being darted - second to the Little Book Cliffs
    mustangs in Colorado, which also seem to have a reputation for being
    "almost tame." The darting has been done there for eight years now.

    On Assateague Island, they've been able to reduce population growth
    without a single roundup - using PZP.

  2. More from TJ who has taken a course on darting wtih PZP.

    A couple of noteworthy mentions from "claims" I've seen:

    * Yes, mares continue to come into heat; PZP is not a hormone - it's a
    protein. It simply blocks contraception by preventing a stallion's sperm
    from connecting with the mare's egg.

    * Stallions do not "rape" mares. This, to me, is one of the most hideous
    misconceptions. Rape is wholly human - and it's certainly not about sex
    or even procreation, it's about domination.

    * Mares do not "become masculine" on PZP. Again, it's a protein (made of
    pig ovaries, actually - PZP = porcine (pig) zona pellucida (the lining
    of the egg), not a hormone.

    * While I believe the timing of PZP application can have an effect on
    foaling timing, PZP does NOT "cause" out-of-season births. We've had
    three mares have late foals (late July, early September and
    mid-September) on PZP-22, and we've had two mares have late foals (late
    July and mid-September) who've either never received PZP-22 (the
    mid-Sept. foaler) or the foal was not affected by the PZP-22 (given when
    she was already pregnant). Late births happen in nature. There is no
    "rutting" season like with deer and elk. Seasonality affects mares'
    cycles, but they can come into heat throughout the year - obviously.

    * And related to above, neither PZP-22 nor PZP affect a fetus a mare may
    be carrying. It affects ONLY the egg by blocking stallion sperm. It does
    this by warning the mare's immune system (hence "immunocontraceptive")
    to be resistant to what her body sees as an invasion - also why it's
    called a "vaccine" - it boosts the mare's immune system like the flu
    vaccine boosts ours.

    Thank you for starting this discussion! It needs more attention and less

    Oh, one more thing: PZP and PZP-22 are different vaccines, not
    interchangeable terms. PZP is the "native" drug given annually. Much
    more research has been done on it (this is the one created in 1972 and
    used on Assateague and Little Book Cliffs among other herds). PZP-22 is
    newer - two HSUS studies are ongoing right now on PZP-22: in Sand Wash
    Basin, Colo., and in Cedar Mountains, Utah. The application timing of
    PZP-22 seems to be fairly narrow for best results and it doesn't really
    seem to work for 22 months. PZP-22 was given to five Spring Creek Basin
    mares at the August 2007 roundup; it worked on one mare. We are
    proposing a program of annual PZP darting to start with next year's
    roundup. We're still waiting to hear ...

    This is a really long comment ... But those guidelines you mentioned
    above are very important, and PZP meets all of them. While I wouldn't
    say there are "no" side effects to PZP, what are the effects of chasing
    horses with helicopters, of shredding family units, of completely
    removing genetic material from herds? What is the $ cost of roundups ...
    of warehousing all those horses?? PZP costs $25/dose with a $2.15 dart.
    Training and the daring rifle extra. :) It IS reversible, and it can be
    administered without ever touching/gathering/immobilizing the mare.

  3. I'm not as knowledgable as you and others, but it sure sounds good to me. So, you're looking at about $27.15/plus man hours to keep a horse from getting pregnant for a year.

    Would you choose which mares to dart, or would be a situation where they'd dart whichever ones they get get a shot at? I would think you'd want certain mares to continue breeding and others to not?

  4. I'm wondering, do you know if Pickens has addressed this issue at all? Though her efforts seem admirable, I guess this is really a critical issue that needs to be addressed for the benefit and health of the mustangs she wants to help.

  5. From TJ
    Basically yes - as far as the cost. I forgot about the cost of the adjuvant to mix the PZP, but it's very low cost, I think about $18 for the little "vial," which gives you about 18 mixes, so about $1 a dose. I like to tell people "less than $30 per mare."

    I very much hope BLM will approve our proposal ... and then, yes, I hope they will allow me to help choose which mares - given that I know them best. My vague plan (until it's approved, when it will become very specific) is that, first of all, all the mares released at the end of the roundup will be given the primer (this is likely to be no more than five mares, if the same happens in 2011 as in 2007), then the mares not rounded up will be darted with primer in the field. After that, BLM will need to determine how many mares of the total to dart based on what management goals they have (I think/hope this will result in an updated Herd Management Area Management Plan (ours is from 1984, I think)). Boosters will be given to those mares in the spring. First priorities for mares to be darted will be young mares - 2-4 - and older mares. Basically, make sure the young mares are healthy to start having babies and the older mares get a break. I think the best thing to do is plan each year which mares get darted and not leave it to chance.

    I don't know whether Madeleine Pickens has addressed this issue ... But I do know PZP is being used in several private wild horse sanctuaries. I think MP is talking about taking geldings from holding, so unless that changes, she wouldn't need to administer PZP. One thing that bothers me with the Pickens plan is that those horses would NOT be in natural wild-horse dynamic families. I'm not sure how she plans to address that, either.


Please feel welcome to join our discussion by telling us about your own thoughts and experiences.