Immunocontraception comes of age
From ANIMAL PEOPLE, January/February 2003:
BILLINGS, RENO, WHITEHORSE–Immunocontraceptives for dogs,
cats, and deer are still not quite here yet, but widespread
applications and planned deployments involving bears, elephants,
wolves, and wild horses indicate that immunocontraception of
wildlife may at last be close to losing the qualifying adjective
“experimental”– at least in the species that are easiest to inject
and keep track of.
New Jersey Department of Environ-mental Protection
commissioner Bradley Campbell announced in November 2002 that his
agency hopes to test immunocontraceptives to control bears this
spring. The New Jersey bear population has increased from an
estimated 100 in 1970, when the state last opened a bear hunting
season, to as many as 2,500 according to much disputed official
figures. An attempt to resume bear hunting in 2000 was quashed by
adverse public opinion.
Immunocontraceptive injections given to 25 bears at the Bear
country USA safari park in South Dakota in 2001 totally halted
reproduction in 2002, University of California School of Veterinary
Medicine professor Irwin Liu told Patty Paugh of the Newark
Hunters in the U.S. have vocally opposed wildlife
contraception experiments for more than 30 years, arguing that
reducing wild animal populations should be left exclusively to them.
Hunting lobby pressure has even obtained short-lived bans on wildlife
contraception in some states, and banning wildlife contraception is
often a provision of so-called “hunters’ rights” bills when
introduced, though so far this has not been part of any such
statutes as enacted.
In British Columbia and the Yukon, however, hunters are
funding wolf sterilization this winter in hopes of rebuilding
populations of moose, bighorn sheep, and caribou that were shot
down to less than stable levels, and purportedly now cannot
withstand even normal natural predation.
As in Alaska, where the state has sterilized wolves to limit
predation since 1999, most of the Canadian wolf sterilizations are
done by conventional surgery. The Canadian wolf sterilization
programs reportedly also involve lethal culling, as packs are
diminished to just the alpha pair. However, Yukon territorial
government biologist Michele Oakley disclosed in November 2002 that
immunosterilants had been injected into some wolves who were caught
in the vicinity of the Fortymile herd, which ranges into Alaska.
Oakley said that the immunosterilant approach would be quicker to use
and less disruptive to the wolves than conventional surgery, if it
proves to be as effective.
Culture & politics
Calling immunocontraceptive applications “experimental”
remains convenient for wildlife agencies inching toward acceptance of
the technology, but with many species the greater part of the
experiment now involves public relations.
Along with hunters, wild horse advocates, philosophical and
religious opponents of any form of intervention in natural life
cycles, and even some strict vegans object to immunocontraception,
the latter because the standard immunocontraceptive, porcine zona
pellicida (PZP), is produced from the ovaries of pigs who have been
slaughtered for meat.
There is also considerable resistance to immunocontraception
ingrained in the culture of wildlife agencies, including some of the
agencies now giving it a try.
At Kruger National Park in South Africa, for instance,
elephant specialist Ian Whyte told Agence France-Presse in October
2002 that immunocontraception experiments with elephants had worked,
but that immunocontraception would not be as practical as either
hunting, culling, or relocation in stabilizing or reducing the
Kruger population of about 10,500 elephants. Whyte estimated,
reasonably enough, that about 4,000 elephant cows would have to be
innoculated each year, after receiving three PZP doses to start the
process, but he also postulated that each elephant would have to be
radio-collared to keep track of which elephants had already been
dosed, which could be avoided by use of small colored ear tags or
fluorescent tattoos, and spoke as South Africa was preparing to seek
permission from the Convention on International Trade in Endangered
Species triennial meeting in Santiago, Chile, to raise funds for
wildlife conservation by auctioning stockpiled ivory from culled
Wildlife management, evolving out of gamekeeping, has
historically focused on creating an abundance of hunted species. The
newer task of conserving and propagating endangered species was
accepted relatively easily, since it also had the goal of creating
abundance, typically achieved by protecting habitat and preventing
poaching and preda tion.
Now wildlife agencies are being asked to limit the numbers of
animals of species that they worked long and hard to make abundant in
the mistaken belief that growing numbers of hunters would suffice to
Instead, while the populations of deer, elk, black bears,
and other hunted species soared to their recorded highs in recent
years, the U.S. hunter population plummeted from 21 million in 1981
to 13 million or fewer today, while the average age of hunters rose
from 36 to 46–a clear sign that recruitment of young hunters is
running far behind attrition among older hunters who are quitting or
Suddenly hunting license revenue is no longer the only
important revenue stream for many agencies, which are having to
compete for money from general funds even to fulfill their
traditional roles in wildlife law enforcement. The agencies are
having to learn to cater to nonhunting taxpayers, who do not want
hunters in their back yards, or parks, and increasingly often
object to use of lethal solutions to deal with problematic wildlife,
especially if nonlethal solutions exist.
Except for predator control, which typically involves
killing animals who are few relative to their prey, wildlife
agencies rarely tried until recent years to reduce wildlife
populations by any means other than hunting.
BLM first to accept
The one major exception in the U.S. may be the Bureau of Land
Management wild horse and burro program, which since 1972 has
removed equines from BLM property, offering them for public adoption.
The BLM wild horse program is very small compared to most
U.S. wildlife agencies, and is staffed mainly by people with
backgrounds involving hooved livestock. As the horses and burros are
considered an invasive alien species by the National Park Service,
Fish and Wildlife Service, Forest Service, and most state wildlife
departments, the BLM wild horse program is something of a wildlife
In 1996 the BLM wild horse program stepped even farther
beyond the confines of the wildlife management old boys’ club by
becoming the first U.S. wildlife agency to accept immunocontraception
as an approved-and-available tool, ready for use wherever it might
be deemed appropriate.
Immunocontraception pioneer Jay F. Kirkpatrick, the longtime
director of conservation at ZooMontana in Billings, began testing
experimental versions of PZP on wild horses in 1975.
Field-testing among wild and free-roaming horse herds was
initially done at Assateague Island, off coastal Maryland and
Virginia. In 1995 the technology was approved for mainland use.
Experiments with western wild horse herds began a year later– but
the Bureau of Land Management has proceeded slowly, in part due to
opposition from wild horse advocates who view either horse removals
or immunocontraception as unjustly favoring cattle over horses.
“We believe that immunocontraception is far more humane than
conducting roundups on a routine basis, which break up social
structures,” Fund for Animals coordinator for the Rocky Mountain
region Andrea Lococo recently told Mike Stark of the Billings Gazette
“We don’t believe immunocontraception is a silver bullet,”
Lococo continued. “The BLM needs to examine all of its options.
There are a lot more than just fertility control,” including
allowing horses to return to management zones from which they have
been eliminated, and increasing the share of forage allocated to
horses rather than cattle.
In fall 2002 the BLM tested PZP on 15 mares from the Pryor
Mountain herd in rural Wyoming. The mares “were shot with a dart
containing PZP, which blocks fertility for one breeding season,”
explained Stark. “The fertility control program targets young and
old mares,” he continued. “Giving the contraceptive to a 2-year-old
mare, BLM officials say, gives the horse an extra year to grow and
mature before getting pregnant. The result should be a healthy foal
and mare. For older mares the yearly breeding cycle can be
difficult,” with adverse effects on the foals. Thus if older mares
do not conceive every year, the foals they do have are also expected
to be healthier.
The BLM is reportedly now considering a test of PZP among the
300-horse McCullough Peaks herd in Wyoming. The McCullough herd is
struggling due to a summer drought that left little fodder beneath
the snow. The cost of using PZP has dropped during the past decade
from about $2,000 per horse to as little as $20 per horse, but the
range managers are still reluctant to spend the money, BLM wild
horse specialist Trish Hatle told Associated Press in late December.
Immunocontraception may nonetheless be the longterm answer to
the perennial squeeze the BLM occupies between ranchers who want to
be rid of competition from horses for grass and water, especially
during drought years, and activists who want the cattle to go. The
adoption market for wild horses is glutted, easing adoption
requirements increases the risk that horses will be “adopted” only to
be sold to slaughter as soon as the BLM turns over title to the
adoptors (supposed to be one year from the date of adoption),
keeping large numbers of wild horses in holding pens has long
strained the BLM wild horse program budget, the BLM has no budget
for establishing more permanent sanctuaries for wild horses, and the
two most discussed alternatives at present are also problematic.
Slick Gardner’s idea
The first alternative, raised by vegetable grower, auto
racer, and lifelong horse enthusiast Slick Gardner of Buellton,
California, would be to persuade Congress to allow ranchers with BLM
leases to convert cattle and sheep grazing allowances into horse
grazing allowances. This would make possible a mutually beneficial
Currently, ranchers pay the BLM a specified grazing fee per month
per head of cattle or sheep allowed to occupy the leased land. The
BLM meanwhile removes wild horses deemed to be in excess of what the
land can support, and buys hay to feed them.
Gardner reasons that a more cost-efficient alternative would
be to compensate ranchers for accepting more horses in exchange for
grazing fewer cattle or sheep. For example, if a rancher starts out
with 10,000 cattle on land with 100 wild horses, the grazing fee for
1,000 of the cattle might be waived as an incentive to remove 1,000
cattle to make room for an additional 1,000 horses. Then the land
would support 9,000 cattle and 1,100 horses. Instead of the rancher
paying the BLM to graze 10,000 cattle while the BLM paid to buy hay
for 1,000 horses, the rancher would pay the BLM to graze 8,000
If a rancher who now grazes 10,000 cattle on BLM land took
5,000 wild horses, the cattle would in effect graze free–but the
rancher would still be obligated to do all the maintenance of fences,
wells, fire breaks, and other land improvements that ranchers do
now, with only half the income from selling cattle. Gardner
believes this would nonetheless make ranching more profitable while
saving the BLM money.
If the rancher took 10,000 wild horses and grazed no cattle,
the grazing fees for the horses would be paid to the rancher,
amounting to a salary for becoming, in effect, a wild horse
The exact value of cattle grazing fees relative to horse
grazing fees could be negotiated.
Gardner believes that any reasonable conversion allowance
would be sufficient to persuade many struggling cattle ranchers to
get out of the cattle industry entirely and instead establish a wild
horse range on contiguous properties, with immense value as a
tourist draw. A vast wild horse range with few if any domestic
cattle or sheep, Gardner points out, could also tolerate a strong
population of wild horse predators such as pumas, wolves, and
grizzly bears–and scavengers, such as the recently reintroduced
California condor. Implementing the entire plan, Gardner argues,
would be better for all the animals and people involved, and would
cost much less than maintaining the status quo.
Immunocontraception might never be needed under the Gardner
scenario, but would be available to use if natural predation on a
horse range such as he envisions could not keep the horse population
Send wild horses to Mexico?
The other most discussed alternative to the wild horse
management status quo, advanced by Merle Edsall of Avon, Montana,
would be to relocate up to 10,000 horses to the northern Sonora
desert in Mexico, southeast of the Sonora Biosphere Reserve. The
very dry region, which already has a small wild horse population,
is heavily traveled by would-be illegal immigrants to the U.S. and
the “people-smugglers” who help them cross the border.
Partners in the horses-to-Mexico scheme include retired
McDonnell-Douglas vice president Philip Edsall, Sonora rancher
Humberto Hoyhos, and Johannes von Trapp, one of the younger members
of the family whose story was told in the 1963 film The Sound of
Music, who went on to build the Stowe ski resort in northern Vermont.
National Wild Horse and Burro Program group manager John Fend
advised in August 2002 that the relocation to Mexico would remove the
horses from the protection of the 1971 Wild and Free Ranging Horse
and Burro Act, and would therefore require Congressional action to
implement. Fend pointed out that the requirement of an authorizing
Act of Congress forestalled further development of a 1989 proposal to
send wild horses to Mexico.
“Although Mr. Edsall’s plan seems like a benign solution to
rancher/mustang conflicts on the surface, the likely outcome is much
grimmer,” opined the Humane Society of the U.S. “In 2001, 626,000
horses were slaughtered in Mexico.”
Added Christopher J. Heyde of the Society for Animal
Protection Legislation, the lobbying arm of the Animal Welfare
Institute, “Mexico has neither the laws nor the needed law
enforcement to ensure the protection of such a huge influx of wild
horses. We have been in contact with several of our Mexican
colleagues, and they share our concerns.”
“Our position,” Fund for Animals president Mike Markarian
told ANIMAL PEOPLE, “is that if the BLM cannot even prevent horses
in the U.S. from [illegally] going to slaughter, how on earth are
they going to protect horses who are no longer in our jurisdiction?”
The big money in selling wild horses to slaughter, Slick
Gardner observes, involves selling the foals of mares who are
adopted while pregnant. Gardner believes this is about half of all
the mares who are removed from the wild each winter. Since the foals
are not branded, they can be sold without risk of being identified
as ex-BLM horses. Gardner estimates that 10,000 wild horses
relocated to the Sonora desert might produce a sustainable saleable
yield of about 2,000 foals per year. That could happen on the
privately managed horse range he envisions in the U.S., too, but in
the U.S. the fate of foals could be better monitored–and the use of
immunocontraception could prevent the births of any horses beyond
those needed for normal herd replacements.
Frustration with deer
The Holy Grail sought by immunocontraceptive researchers ever
since investigation of the idea began is finding a safe and effective
method of preventing births of deer and elk.
This is potentially the most lucrative use for
immunocontraception, since it involves protecting the lives,
property, and sensibilities of affluent suburbanites who like to see
deer and mostly disapprove of recreational hunting, but do not like
to share their rose bushes with deer, hit deer on the road, or get
Lyme disease from deer ticks that they associate by name with deer,
even though the ticks are carried mainly by mice.
The administrators of suburbs, parks, and university
campuses where hunting and sharpshooting are unpopular and unsafe are
believed to be willing to pay a premium price to use any deer control
method that does not offend the majority of voters and taxpayers.
Therefore immunocontraceptive developers have concentrated most of
their research-and-development budget over the past decade on
experiments involving deer and elk, even though deer and elk have
turned out to be among the hardest species to use immunocontraception
Earlier, deer defeated attempts to limit their numbers by
using hormonal and chemical contraceptives. In one of the first such
experiments, at Angel Island in San Francisco Bay, California,
some hormonal contraceptives for deer actually appeared to stimulate
Deer appear to be less able to defeat immunocontraceptives by
adjusting their body chemistry, but finding safe and effective
delivery methods remains an elusive goal.
Jay F. Kirkpatrick, physiology professor John W. Turner of
the Medical College of Ohio at Toledo, and Alan Rutberg of Tufts
University have been field-testing immunocontraceptives for deer and
elk since 1993 without achieving unequivocally positive results.
Critics of immunocontraception recite failures, ambiguous
findings, and program cancellations, mostly associated with
complications of delivery, at Fire Island, New York, 1993-present;
Amherst, New York, 1996, where the planned trial never got
underway due to opposition from hunting lobbyists; the Frelignhuysen
Arbortem in Morris Township, New Jersey, 1997; and Irondequoit,
New York, near Rochester, 1997-1999.
At Irondequoit the technology worked, but took an average of
46 volunteer hours per deer to administer and monitor, according to
State University of New York College of Environmental Science and
Forestry professor William F. Porter, who headed the on-site
The Fire Island experiment has now achieved a 40% reduction
of the deer population, says Kirkpatrick, but it came close to
cancellation several times when residents were unable to see quick
Despite the setbacks and expense, however, the need to
produce a cost-effective, foolproof birth control method for use in
deer and elk has escalated in urgency throughout the U.S. during the
past year, due to the detection of chronic wasting disease among
both wild and captive deer and elk herds. Closely related to mad cow
disease and also believed capable of killing humans who consume
infected brain or nerve tissue, CWD is now known to occur in most
states north of the snow line. Although state wildlife agencies
eased restrictions on doe hunting, raised bag limits, and urged
hunters to kill deer whether or not they planned to keep the meat,
hunting participation reportedly dropped during late 2002 because
many hunters were unwilling to spend the money and time necessary to
hunt without at least the pretext of getting meat.
If CWD can be stopped, observers increasingly believe, the
effort will require completely eliminating the deer and elk
populations of the afflicted areas. All reproduction must be halted
until the disease is gone and the means by which it passes among deer
and elk is fully understood.
PZP trials are now underway at the Western North Carolina Nature
Center in Asheville and are under consideration by public officials
in Princeton Township, New Jersey, and Beverly Shores, Indiana.
Other methods, however, are getting another look.
The National Park Service and Colorado Division of Wildlife
began testing a new hormonal contraceptive called leuprolide at Rocky
Mountains National Park in mid-2002. Manufactured by Atrix
Laboratories of Fort Collins, leuprolide has been tested at the
C-DoW research station in Fort Collins since 1999. Biologist Dan
Baker reported that leuprolide met the requirements of being
reversible, working 90% of the time, not harming the meat of
animals who might be hunted, and not changing what Denver Post
environment writer Theo Stein described as “the breeding behavior
that brings busloads of tourists to the park each fall.”
Highland Park, Illinois, in January 2002 teamed with the
University of Wisconsin at Madison and the Milwaukee County Zoo to
test surgical sterilization of deer. Nineteen does were given tubal
ligations during the next four months. The results are now being
monitored. Previous experiments with surgically sterilizing deer
have failed, outside of zoos, because capturing, anesthetizing,
and operating on the does tends to put them under life-threatening
stress, because the procedures are expensive, and because other
deer immigrate into under-occupied suitable habitat.
PZP is still seen as best bet
Immunocontraception remains the technology of most promise in
the wildlife contraception field.
Extensive zoo and laboratory trials of PZP on species ranging from
dogs and cats to the pygmy hippos at the Amsterdam Zoo in The
Netherlands demonstrate that wherever doses can easily be given and
the outcome can be observed, PZP injections are safer and more
reliable than the older hormonal and chemosterilant animal birth
Immunocontraceptives such as PZP work by tricking the immune
system of a female animal into attacking the sperm cells of a male of
her species with her own natural antibodies, as if the sperm were an
invading infection. The process involves less alteration of body
chemistry than the hormonal approach used in birth control pills for
humans, and in the oral contraceptives thus far available for
animals, which trick the female body into responding to sperm as if
Immunocontraceptives are also believed to be gentler than the
chemosterilant methods used in the current generation of injectible
contraceptives for male animals, which are gentle enough that one
such product, Neutrosol, has also been deployed recently in
increasingly ambitious field trials hosted and sponsored by humane
organizations–among them the Arizona Humane Society, Humane Society
of Missouri, Humane Society International division of the Humane
Society of the U.S., and the North Shore Animal League America.
Because immunocontraceptives are designed to be
species-specific, they tend to be safer for use in the wild than any
substance which might affect a range of species.
Hormonal contraceptives and chemosterilants are not currently
known to have second-hand effects, but with immunocontraceptives
there is believed to be little way that second-hand effects could
occur even by fluke.
Oral versions, dogs, cats
In addition, immunocontraceptives offer some hope that the
dosage might eventually be embedded in edible bait-balls designed to
attract only the target species and gender. This would be slightly
more difficult than administering species-specific oral rabies
vaccination, now done successfully in Europe for more than 20 years
and in the U.S. for more than 10 years. As male and female animals
often have different scent preferences and tastes in food, producing
a gender-specific bait is theoretically possible.
For now, however, delivering an immunocontraceptive dose
still depends upon either darting the animals or tranquilizing them
for conventional injection.
This in turn is one of the obstacles to producing
immunocontraceptives for dogs and cats. The smaller the animal, the
riskier either darting or tranquilization tends to be. Many of the
street dogs common to much of the world could be caught and injected
with relative ease, but injecting an immunocontraceptive dose into a
frantic feral cat might only be possible with use of a squeeze-cage,
and then only with difficulty. Further, once a cat is held securely
enough to innoculate safely, a high-speed spay surgeon using gas
anesthesia could do a conventional spay in just a few more minutes.
There are enough advantages to surgical sterilization, in
terms of producing permanent results and modifying problematic
behavior, and the cost difference between immunocontraception and
surgical sterilization would be low enough if an animal was already
captured, that going ahead with the surgery might remain the
preferred choice for dealing with any animal who might be socialized
for adoption or be released anywhere that she could disturb neighbors.
Surgical sterilization produces a very slightly higher risk
of post-operative infection than administering an injection, all
other factors being equal, but many high-speed clinics that
emphasize a sanitary surgical environment already count
post-operative infection cases in numbers per thousand or even 10,000
animals handled–a rapid advance from the standards of barely a
decade ago, when post-operative infection cases were counted in
numbers per 100.
Street dog and feral cat rescuers, especially in
underdeveloped parts of the world, are often still working in
environments where trying to achieve sanitary conditions is nearly
impossible, and post-operative infection remains routine. However,
as Jeff Young, DVM, recently pointed out in a conversation with
ANIMAL PEOPLE about his experience in teaching sterilization
technique abroad for the Spay/USA division of the North Shore Animal
League America, a veterinarian who cannot perform clean surgeries
probably cannot perform consistently clean injections either. The
answer therefore is to do a better job of impressing upon vets the
need to maintain sterile operating facilities.
Great savings are unlikely to be realized through replacing
surgical sterilization with immunocontraception until
species-specific and gender-specific oral delivery systems are
perfected. Until then, what savings there might be would probably
be more significant in a wealthy nation whose veterinarians command
high wages than in a poor nation where–as in India–the typical cost
of sterilization surgery on a dog or cat ranges from $5.00 to $10.00,
plus the cost of several days of post-operative care to avoid the
complications of infection which in the U.S. are rarely a worry.