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Copyright 2008 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any editorial material, artwork and photos is strictly forbidden without express written permission of the publisher. For information about reprint rights, please contact the editor; editor@rockymountainrider.com.
May 2008 Issue
One humane way of dealing with wild horse overpopulation is
contraception. However, contraception does not reduce
population rapidly, and it often increases the lifespan of treated
animals, which do not go through the stress of pregnancy and lactation.
Porcine zona pellucida, or PZP, has been tested as a
contraception for many wild animals since 1989, including white-tailed
deer, black bears, tule elk, African elephants, llamas and alpacas, and
wild horses. It was developed to be an effective and humane alternative
to other methods of controlling animal population, such as roundups or
killing. When the vaccine wears off in a minimum of one year, normal
conception and birth is usual.
PZP was developed into a viable vaccine at UC Davis, in
The BLM currently spends about $200 per year to vaccinate each
wild mare, and this includes the cost of the vaccine at $21 per dose,
plus handling costs.
The total cost of the wild horse contraceptive program is about
$250,000 per year. In comparison, housing and preparation for adoption
of wild horses costs about $19 million annually. The PZP Wildlife Contraceptive Group, which
carries out the active research on PZP, is made up of The Science and
Conservation Center (in Billings, Montana), The University of California
– Davis, the Medical College of Ohio, the University of Iowa, and the
HSUS.
“We supply PZP to inoculate about 1,200 wild horse mares now
each year,” said Jay. F. Kirkpatrick, PhD, Director of the The Science
and
“Although the vaccine has a 90% success rate the first year,
the efficacy of the vaccine is not the most important thing — the
percentage of mares treated on the range is the important thing.
“The National Park Service has been using PZP on
“After a herd reaches the new age of mortality, then the herd
population reduction begins overall. The National Park Service is using
PZP to keep herds at a manageable level on Assateague and at four other
locations. We are now beginning to inoculate wild horses at horse
sanctuaries in
The National Park Service is also performing DNA tests on small
herds of horses to ensure that isolated populations continue to carry
the genetic traits that have made them unique.
When asked how he saw the future of PZP and population control,
Kirkpatrick replied, “The National Park Service will continue to use
PZP and to solve their wild horse overpopulation. I have no idea what
the BLM will do – they are blocked by social, cultural, political and
economic problems.
“As to the domestic horse population, humans continue to breed
horses with human-imposed values, and if they do not measure up, they
are discarded. The Pryor Mountain Wild Horses are more biologically fit
than anything you can find in a breeding operation.”
Some wild horse advocates worry that as the vaccine wears off at
different times of the year and mares may become fertile in fall or
winter, foals are sometimes born during winter, and that this is a
severe hardship for both foals and lactating mares, especially in places
like the rugged Pryor Mountains of Montana and Wyoming, or the high
desert of southeastern Oregon where the Kiger mustangs live.
A study done with the Assateague, What is PZP? How does it work?
A membrane known as zona pellucida (ZP) surrounds all mammalian
eggs, and allows the attachment and penetration of sperm to the egg
during fertilization. When pig ZP (PZP) is injected into a female
animal, the female animal’s body produces antibodies. These antibodies
attach to the female’s ZP proteins and prevent sperm from attaching to
the membrane, blocking fertilization. PZP can be given to pregnant
females without harming the fetus.
Each female animal needs to be injected twice, with the first
injection being up to a year before a booster, to provide contraception
for about a year in approximately 90 percent of treated females. A
newer, one-injection method, with part of the vaccine being
time-released, has been shown to be nearly as effective and is
longer-lasting.
PZP is either injected by hand, or, as is more common, delivered
via a dart fired from a dart rifle. After hitting the animal in the hip
or rump, a small powder charge injects the vaccine and the dart falls
off. The brightly colored dart is then retrieved.
Because PZP does not interfere with or prevent heat cycles and
breeding, wild horse herd social behavior is not as affected as it would
be if the horses were sterilized.
Copyright 2008 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any editorial material, artwork and photos is strictly forbidden without express written permission of the publisher. For information about reprint rights, please contact the editor; editor@rockymountainrider.com.
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