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Theriogenology 66 (2006) 126–134
www.journals.elsevierhealth.com/periodicals/the
Contraception in felids
Linda Munson *
Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine,
University of California, 1 Shields Ave., Davis, CA 95616, USA
Abstract
Contraceptives are used for reversible reproductive control in genetically valuable wild felids, as permanent reproductive control
in generic wild felids, and as an economically practicable means to control feral cats. The progestin contraceptives, megestrol
acetate, melengesterol acetate, medroxyprogesterone acetate, and levonorgestrol (administered orally, in implants, or as depot
injections), are effective in preventing pregnancy. However, long-term use is associated with endometrial hyperplasia, endometrial
cancer, and mammary cancer. Gonadotropin releasing hormone analogs or luteinizing hormone vaccines that achieve contraception
by suppressing ovarian or testicular function, do not have the adverse health effects of progestins. However, reliable reversibility has
not been demonstrated, and male secondary sex characteristics may be suppressed. Bisdiamines also inhibit spermatogenesis and
lower circulating testosterone concentrations in treated male cats. Porcine zona pellucida vaccines are ineffective contraceptives in
felids and may cause serious health problems when combined with some adjuvants. Because of the limited availability of nonprogestin contraceptives and side effects associated with some agents, widespread application of contraception to felids has been
curtailed. More non-steroidal methods of contraception should be tested in the future to provide alternatives for controlling
reproduction in felids. Furthermore, all empirical information on contraceptive safety and efficacy should be assembled in a
database to provide the knowledge needed by veterinarians and managers to determine benefits/risks of currently available
contraceptives in felids, both domestic and wild.
# 2006 Elsevier Inc. All rights reserved.
Keywords: Contraception; Felid; Progestins; Deslorelin; Bisdiamines
1. Introduction
The fecundity of many felid species has necessitated
sterilization or contraception to prevent overpopulation.
Whereas ovariohysterectomy or ovariectomy alone has
been the method of choice for most domestic cats,
reproductive management of threatened or endangered
zoo-maintained felids requires safe and reversible
contraception. The goal of felid conservation breeding
programs in zoos is to retain at least 90% of the genetic
diversity of a species over the next 100 years. Because
space and resources are limited, zoo managers require
* Tel.: +1 530 754 7567; fax: +1 530 752 3349.
E-mail address: [email protected].
0093-691X/$ – see front matter # 2006 Elsevier Inc. All rights reserved.
doi:10.1016/j.theriogenology.2006.03.016
contraception to limit reproduction of less geneticallyvaluable felids and to implement the conservation goals
of species survival plans. Contraception as a form of
reproduction control also is increasing in free-living
wild felid and feral domestic cat populations, because of
its preference by the public over lethal methods. If
easily-delivered, safe, and effective contraceptives were
readily available for domestic cats, catteries producing
animals for the pet trade and some pet owners likely also
would choose these methods over surgical sterilization.
However, to date, widespread use of contraceptives has
been limited in felids by safety concerns and the lack of
effective choices.
Few contraceptives are commercially available, and
none have been approved by the Federal Drug Administration (FDA) for contraceptive use in felids. Thus, all
L. Munson / Theriogenology 66 (2006) 126–134
contraceptive use in cats is extra-label (for FDA-approved
drugs) or experimental (for unapproved methods). Most
contraceptives were developed for humans and have only
been tested for efficacy and safety in that species or a few
laboratory animal species (usually rodents, the domestic
dog, or non-human primates) [1]. Because reproductive
function in the female cat (characterized by seasonal
polyestrus and induced ovulation), differs considerably
from that of the tested species, the effects of human
contraceptives on felids are unknown. Drug metabolism
in cats also differs from humans [2,3]. Therefore, whereas
any surgical procedure or drug administration carries
some risk, extra-label drug use in felids may pose special
problems. Extra-label use of contraceptives will always
be required for wild felids because controlled clinical
trials are virtually impossible to conduct due to small
population size and geographic disparity in location.
While such clinical trials are feasible in the domestic cat,
such testing requires considerable expense. Although
some contraceptives have been tested for use in domestic
cats (both as the target species and as a model for wild
felids [4,5], conducting more studies should be a priority
and ultimately would promote more large-scale contraceptive use in cats.
Several excellent (albeit outdated) reviews of contraception in cats have been published [6–10]. This review
intends to provide an update on current contraceptive
methods and research in felids as a taxonomic group
including both wild and domestic felids. While
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permanent reproductive control can also be accomplished through sterilization, only reversible methods for
preventing pregnancy will be included in this review.
2. General methods of preventing pregnancy
Contraception in its broadest sense is preventing the
birth of offspring while maintaining the potential for
fertility. Contraception can be achieved by preventing
gamete formation, conception, or implantation, as well
as by disrupting pregnancy (causing resorption or
abortion). Contraceptives are more widely used in
females where the intricately orchestrated events
leading to oogenesis, ovulation, gamete transport,
and implantation are more easily disrupted than is
spermatogenesis in the male. Reproductive cyclicity
and gametogenesis in both sexes can be disrupted by
administrating exogenous hormones that interfere with
the normal hypothalamic/pituitary/gonadal axis, prevent hormonal synthesis or release, or interfere with
endocrine activity at the tissue level. Spermatogenesis
also can be directed arrested by some chemicals.
Fertilization can be averted by physically blocking the
reproductive tract, altering the uterine milieu necessary
for sperm movement, or interfering with sperm–egg
binding necessary for fertilization. Specific examples
of these concepts are outlined below, and the
commerically-available contraceptives are listed in
Table 1.
Table 1
Commercially-available contraceptives for felids
Contraceptive
Brand name
Source
Method of delivery
Progestins
Megestrol acetate
Megestrol acetate
Medroxyprogesterone acetate
Medroxyprogesterone acetate
Melengesterol acetate
Levonorgestrol
Ovaban1
Megace1
Provera1
Depo-Provera1
Nonea
Norplant1
Schering-Plough
Bristol-Meyers Squibb
Pfizer Inc.
Pfizer Inc.
ZooPharm
Wyeth-Ayerst
PO
PO
PO
IM
Implant
Implant
Androgen
Mibolerone a
Cheque1 Drops
Pfizer Inc.
PO
GnRH analogs
Deslorelin
Leuprolide acetate
Leuprolide acetate
Suprelorin1
None
Lupron Depot1
Peptech Animal Health
ZooPharm
TAP Pharmaceuticals
Implant
IM depot
IM depot
Immunocontraceptive
Porcine zona pellucida vaccineb
Porcine zona pellucida vaccineb
SpayVac1
None
TerraMar Environmental Research Ltd
Zoo Montana
IM
IM
Chemical contraceptive
Bisdiamine WIN 18,446
Fertilysin1
SAF Bulk Chemicals, Milwaukee, WI
PO
a
b
Mibolerone can be hepatotoxic and thyrotoxic in felids.
PZP vaccines have not been proven effective in felids.
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L. Munson / Theriogenology 66 (2006) 126–134
3. Methods of administration
Contraceptives for felids are available as implants,
depot injections, pills or liquid for oral administration,
powder for mixing with food, or as vaccines. Regimens
may differ according to the timing of first treatment,
whether coinciding with the active reproductive period,
preceding this period, or during anestrus. Many felid
species are seasonally polyestrous [11], even in a
controlled laboratory environment (Munson, unpublished). Therefore, contraception may be necessary only
during the breeding season. However, it is unknown if
reproductive function will simply be postponed, leading
to fertility after contraception withdrawal, and the
potential birth of offspring during a less optimal season
of the year for raising young. To prevent this uncertainty
and complication, most contraceptives are given to
felids throughout the period in which reproductive
suppression is desired. Ideally, the treatment regimen is
initiated during anestrus to minimize the dose needed
for reproductive suppression and to avert exposure to
endogenous steroids that can cause lesions in reproductive organs.
4. General safety concerns
Designing contraceptives that are effective and
reversible, yet safe, has been the primary challenge
for felids. Agents that disrupt endocrine function
sufficiently to halt reproduction have the potential to
adversely affect hormone target tissues and disturb
metabolic homeostasis. Immunocontraceptives that
target egg and sperm antigens have the potential to
incite immune-mediated damage in other organs
[12,13]. Chemicals that block spermatogenesis are
rarely specific to this process and can cause toxicity in
other organs [14]. For each population or individual
animal, these potential and actual risks need to be
assessed and then weighed against the contraceptive
benefits. The specific side effects in felids are included
under each category of contraception reviewed below.
5. Female contraceptives
5.1. Contraceptives that disrupt hormonal cyclicity,
folliculogenesis, gamete transport, or endometrial
receptivity
5.1.1. Progestins
Commercially available progestin contraceptives
include megestrol acetate [MA; Ovaban1 (tablets),
Schering-Plough, Lafayette, NJ; Megace1 (oral sus-
pension), Bristol-Meyers Squibb, Princeton, NJ],
medroxyprogesterone acetate [MPA; Provera1 (oral
tablets) or Depo-Provera1 (injectable), Pfizer Inc.,
Groton, CT], melengestrol acetate [MGA implant,
ZooPharm, Fort Collins, CO), and levonorgestrel [LNG,
Norplant1 (implant), Wyeth-Ayerst, Chazy, NY]. The
specific mechanism (or mechanisms) by which progestins effectuate contraception is unknown. Proposed
mechanisms include: (1) negative feedback on the
hypothalamus and pituitary gland leading to suppression of GnRH, FSH, or LH secretion and failure of
folliculogenesis and/or ovulation; (2) altered motility of
the tubular tract causing failed oocyte transport and
fertilization; or (3) altered receptivity of the endometrium resulting in implantation failure. Neither the
potent progestin, MGA, in zoo felids [15], nor LNG in
the domestic cat [16] suppressed follicular development
or ovulation, suggesting that hypothalamic and pituitary
suppression is not the means by which these agents
effect contraception. In general, progestins promote
endometrial growth and secretion, as well as smooth
muscle relaxation in the uterus [17–19]. Therefore,
altered uterine motility and endometrial receptivity are
the likely mechanisms for progestin-induced contraception.
Megestrol acetate has been used to suppress estrus in
domestic cats and to reduce litter numbers in feral cats
in Europe [20–24]. This product also has been used as
an oral contraceptive in zoo-held felids [American Zoo
and Aquarium Association Contraceptive Advisory
Group (AZACAG) Database]. Treatment regimens
differ depending on whether treatment is initiated
during anestrus, estrus, or diestrus. In the anestrous
domestic cat, an initial dose of 2.5–5 mg/day for 3–5
days has been recommended, followed by 2.5–5 mg/
week [7,21,25–27]. Cats in estrus may require a higher
dose (5 mg/day until estrus stops, then 2.5–5 mg/week,
PO) [25]. The recommended dose for diestrous cats is
2.5 mg/day PO [27]. Treated cats should be separated
from adult males for at least 1 week to assure efficacy.
Recommended duration of treatment ranges from 2 to18
months, followed by a period of normal estrous cycles
before treatment is repeated [25]. Most MA-treated cats
return to estrus within a few days.
Medroxyprogesterone acetate has been used as a
contraceptive for the domestic cat (companion or feral),
as well as felids maintained in zoos [8,22,28]. An
oral dose of 5 mg/day or a 25–100 mg injection is
recommended for the domestic cat [7]. Estrus is
suppressed for 2–4 months using the injectable form
[7], although treatment every 6 months has also been
recommended [22]. In zoo felids, an injection of 5 mg/
L. Munson / Theriogenology 66 (2006) 126–134
kg body weight is recommended every 2 months
(AZACAG recommendations at: http://www.stlzoo.org/
contraception). A MPA dose of 1000 mg (IM) followed
by a 500 mg (total) injectable bolus every 3 months also
has been effective in suppressing estrus in lions [29].
Melengestrol acetate has been the most widely used
contraceptive in zoo felids, because it provides longterm, reliable and reversible contraception in all zoo
felid species tested (AZACAG dtabase) [29]. MGA also
has been used to control reproduction in free-ranging
lions [30]. This agent is administered in a silastic
implant (Dow Corning, Hemlock, Michigan 48626),
placed SC or IM, providing continual exposure to a
potent progestin [31]. This practical method of delivery
has been invaluable for reproductive management of
non-domestic felids. If left in place, a single implant
(containing 3–40 mg MGA/kg body weight; usual dose
of 20 mg/kg) can prevent pregnancy reliably for at least
2 years. Smaller cats appear to require a higher dosage
(E. Plotka, personal communication).
Levonorgestrel (16 mg in a silastic implant) has been
used to prevent pregnancy in domestic cats for up to 1
year [16]. Nine of ten LNG-treated cats subsequently
became pregnant, demonstrating reversibility after a
single year of treatment. Safety and reversibility have
not been evaluated after long-term use in a controlled
study.
Although progestins have proven to be reliable and
affordable contraceptives for felids, there have been
significant adverse reactions in every species evaluated,
a factor that should be considered before use. The same
activities that make progestins effective contraceptives
(by altering endometrial growth and glandular secretion
and by promoting myometrial relaxation) are the basis
for the serious side effects noted in many progestintreated felids. These effects may be confounded and
accentuated by concurrent exposure to endogenous
estrogens (that up-regulate progesterone receptors) and/
or progesterone [32,33], because many progestintreated felids continue to cycle and ovulate [15].
Progestins also alter glucose metabolism, suppress
adrenal cortical function, and promote growth of the
mammary gland. Together, these actions can have
profound effects on general and reproductive health.
Although most progestin-induced uterine lesions only
cause infertility, mammary and uterine cancers,
pyometra, or diabetes can be fatal.
In the domestic cat, MA treatment has been
associated with development of endometrial hyperplasia and pyometra [22,34,35]. MA treatment also has
been associated with fibroadenomatous mammary
gland hyperplasia [25,36–39], a change that regresses
129
when treatment is discontinued. Additionally, MA and
MPA treatment increases the risk of mammary cancer in
cats [40–42], as well as hair loss and xanthomatosis
[22,39,43]. Some young adult cats treated with
levonorgestrel had mild endometrial lesions, but no
changes in mammary tissue after 1 year of exposure
[16].
In zoo felids, MGA or MA exposure significantly
increased the risk of developing marked endometrial
hyperplasia, endometrial mineralization and hydrometra
[44–46]. Although not life-threatening, these conditions
would likely cause infertility and are irreversible.
Furthermore, felids treated with MGA developed more
serious endometrial hyperplasia earlier in life than
untreated animals [44]. Some MGA-treated felids with
endometrial hyperplasia also developed endometrial
polyps, endometritis and pyometra, [44] conditions that
likely would also result in infertility. Furthermore, most
felids with endometrial cancer and leiomyosarcoma have
been treated earlier with MGA or MA [47–50],
suggesting a causative role of progestins in these cancers.
MGA exposure also increases the risk of zoo felids
developing mammary cancers, most of which progress
rapidly, metastasize widely, and are fatal [51].
Metabolic abnormalities (such as diabetes) occur in
some progestin-treated domestic and wild cats [46,50]
because these steroids can antagonize the actions of
insulin, elevate growth hormone and have direct
glucocorticoid effects [22,46,52–54], all of which can
increase serum glucose [16,55] and cause glucosuria
[56]. Glucocorticoid suppression has been reported in
MA- and MPA-treated, but not MGA- or LNG-treated
cats [29,52,57]. Androgenization, manifested by the
development of a mane, has also occurred in a few
progestin-treated lionesses [29]. Weight gain also
occurs in progestin-treated felids [16,39]. Whether this
is a direct effect of the anabolic actions of progestins or
secondary to decreased activity from estrus suppression
is not known.
5.1.2. Mibolerone
Mibolerone (Cheque1 Drops: Pfizer) is an androgen
that blocks pituitary LH release, thereby suppressing
gonadal function [27]. Mibolerone at an oral dose of 7–
8 mg/day has suppressed estrus in captive jaguars, lions
and leopards [58]. However, concerns about increased
aggression and masculinization (including mane growth
in female lions) have limited its use in zoo animals
[27,58]. In the domestic cat, a dose of 50 mg/day
prevents estrus, but causes masculinization [59], while
lower doses have been ineffective [59]. Because
mibolerone also can be hepatotoxic and thyrotoxic in
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L. Munson / Theriogenology 66 (2006) 126–134
cats at the contraceptive dose, its use in felids has been
discouraged [60].
5.2. Contraceptives that disrupt the hypothalamicpituitary-gonadal axis
5.2.1. GnRH agonists
Steroid hormones of ovarian derivation or from
exogenous sources all promote pathological growth of
endometrial and mammary tissue in felids. So a
contraceptive that suppresses ovarian steroid production would be ideal for cats. One such candidate is the
GnRH agonists, small-sized proteins that, when given
exogenously, override endogenous pulsatile GnRH
that normally regulates pituitary FSH and LH
secretion. Treatment with gonadotropin agonists
initially provokes folliculogenesis and ovulation,
which then is followed by protracted ovarian
quiescence. There are two commercial sources of
GnRH agonist, deslorelin [Suprelorin1 (implant),
Peptech Animal Health, Australia] and leuprolide
acetate [luprolide (slow-release injectable) ZooPharm; Lupron Depot1 (injectable),TAP Pharmaceuticals]. Deslorelin implants are available in 5 mg (for
animals 30 kg) and 10 mg (for animals 30 kg)
doses. Five mg implants have been effective for 6–2
months, and 10 mg implants for up to 2 years in zooheld felids (AZACAG recommendations). Deslorelin
has been proven effective and safe in the domestic cat,
and only the limited availability restricts more
widespread use [4]. This product, delivered in a
6 mg subcutaneous implant to 10 domestic cats,
effectively suppressed ovarian follicular activity for
4–14 months (the latter coinciding with study
termination). No adverse effects were noted except
weight gain. However, eight of 10 cats did not fully
return to normal cycling by the end of the study [4].
Therefore, although GnRH agonists have not been
associated with significant adverse health effects in
the cat, it remains unclear if reproductive cyclity
returns after the administered dose is depleted.
Deslorelin is now being used in captive-held wild
felids, such as the clouded leopard (Neofelis nebulosa)
and cheetah (Acinoynx jubatus), and no adverse
effects have been noted to date [61,62]. However, the
priority for GnRH agonist research is a prospective
and systematic assessment of reversibility in both the
domestic cat and representative wild felid species.
5.2.2. LH receptor vaccination
There has been one study examining the potential of
vaccinating the domestic cat against the LH receptor
using a silastic, subcutaneous implant [63]. Estrous
behavior was suppressed and corpus luteum function
was reduced for 395–516 days without affecting normal
estradiol concentrations [63]. Further studies testing the
efficacy, safety and reversibility of this immunocontraceptive approach are warranted.
5.3. Contraceptives that prevent sperm–egg
interactions
Most immunocontraceptives tested in felids have
targeted the zona pellucida (ZP) antigens that mediate
sperm binding to the egg (native porcine zona pellucida,
PZP; Jay Kirkpatrick, Zoo Montana; SpayVac1,
TerraMar Environmental Research Ltd.) [64–67]. A
disadvantage of this technique is that the cats continue
to cycle, producing endogenous ovarian steroids that
increase the risk of uterine and mammary gland disease
[42,44,68]. The immunogenicity of ZPs also is low
because these antigens are viewed by the immune
system as ‘‘self’’. To enhance the immune response,
they are usually administered with potent adjuvants
[69,70], some of which have been associated with
sarcomas in domestic cats [71].
Several clinical trials testing the efficacy of PZP
vaccines have been conducted in the domestic cat, and
poor contraceptive success has been achieved despite a
robust antibody response. One study tested SpayVac1
with Freund’s complete adjuvant (FCA) or alum in 8–12
week old domestic kittens, and all vaccinated animals
became pregnant in spite of high anti-PZP titers [64]. In
another study using PZP with FCA in adult cats, only
one of five became pregnant [65]. In a third trial
using carbopol as the adjuvant, equivalent numbers
of vaccinated and control cats became pregnant
(L. Munson, unpublished). Taken together, these results
indicate that PZP vaccination does not provide adequate
contraception in the domestic cat. Lack of efficacy may
be due to antigenic differences between feline and
porcine ZPs that limit the blocking effect of anti-PZP
antibodies in the cat [72].
Several safety trials with PZP vaccines have also
been conducted in both zoo felids and the domestic cat
to determine if anti-PZP antibodies cause immunemediated damage to the ovaries [66,67]. Although no
ovarian lesions were noted, marked local reactions
occurred at the vaccination site in all individuals
vaccinated with PZP in FCA or Freund’s incomplete
adjuvant [66,67]. Some domestic cats injected with
FCA with or without PZP developed systemic
granulomas and associated hypercalcemia [66]. Poor
efficacy and considerable safety concerns make PZP an
L. Munson / Theriogenology 66 (2006) 126–134
unattractive alternative for controlling reproduction in
felids.
6. Male contraceptives
6.1. Contraceptives that arrest spermatogenesis by
disrupting the hypothalamic/pituitary/testiscular
axis
The GnRH agonists, deslorelin [Suprelorin1
(implant)] and leuprolide acetate [luprolide (slowrelease injectable)] have been tested for contraceptive
effects in the male domestic cat and certain wild
felids. Both spermatogenesis and testosterone production depend on pituitary LH and FSH secretion, which
is suppressed in the presence of continuously high
GnRH agonist concentrations. Spermatogenic arrest
has been achieved in domestic cats using deslorelin,
and a 6–12 mg deslorelin implant successfully inhibits
fertility in the cheetah and lion after a 6 week delay,
largely by suppressing spermatogenesis [62]. In these
felids, 5 mg implants have been effective for 6–12
months and 10 mg implants for up to 2 years
(AZACAG recommendations). Male aggressive behaviors are reduced in some animals, but not territorial
behavior (AZACAG database). Testosterone-dependent secondary sex characteristics, such as mane
growth in lions, were also diminished. The latter effect
may be of concern to some managers who desire
majestic-appearing lions. Finally, because males
treated with these GnRH agonists may continue to
copulate, co-housed females will remain at risk for
developing diseases associated with prolonged endogenous progestin exposure.
6.2. Chemical contraceptives that directly arrest
spermatogenesis
Several chemicals, such as gossypol, dinitropyrroles and carbamates, can cause male infertility
through multiple mechanisms [14], but most have
other toxic effects, making them unacceptable as
contraceptives. The bisdiamine compounds (amebicidal drugs that target male germinal epithelium) are an
exception and appear to have no harmful systemic
effects [73]. A safety and efficacy trial in the male
domestic cat demonstrated that 150 mg/kg of the
bisdiamine WIN 18,446 (Fertilysin1, SAF Bulk
Chemicals, Milwaukee, WI, USA) administered daily
in food causes near complete spermatogenic arrest in
all treated individuals without damage to spermatogonia [5]. These effects were completely reversible,
131
and no adverse effects on general health, blood
parameters or behavior were noted. However, serum
testosterone concentrations were significantly lower in
treated versus control males. Whether this reduction
was sufficient to cause loss of secondary sex
characteristics is unknown. Testosterone concentrations returned to normative levels within 3 months of
treatment cessation. Although bisdiamines appear safe
and effective for male cats, they can induce serious
teratogenic effects in pregnant females [74], so
administration must be done with care to assure only
males receive the drug. The final limitation to this
approach is that the cost of bisdiamines is currently
prohibitive for most veterinary uses.
6.3. Contraceptives that block sperm outflow: vas
plugs
Occlusive silicone casts of the vas deferens have
been tested for felids as a reversible alternative to
vasectomy (L. Zaneveld, personal communication).
Although sperm outflow is blocked (thereby achieving
the contraceptive goal), local inflammatory reactions
occur due to exuded sperm at the site of plug
placement, making reversibility unlikely (L. Munson,
unpublished). Furthermore, the necessity for skilled
microsurgery makes application of this technique
impractical.
7. The AZA Wildlife Contraception Center and
the Contraceptive Health Surveillance Center
The AZA Wildlife Contraception Center at the St.
Louis Zoo http://www.stlzoo.org/contraception and the
Contraceptive Health Surveillance Center at the University of California at Davis centralize information on
the efficacy and adverse effects of contraceptives in zoo
and wild animals. The Contraceptive Health Surveillance
Center also maintains a database of published information on adverse reactions in domestic animals. Information on contraceptive safety is obtained from pathological
evaluations of reproductive tracts from both untreated
and contraceptive-treated zoo and wild mammals. Lesion
prevalence and severity are then compared between
treated and untreated populations to determine if
contraceptive exposure is a risk factor for lesion
development. Through this surveillance, spontaneous
gynecologic diseases can be distinguished from those
exacerbated by exogenous compounds. Protocols and
forms for submission can be found at the American
Association of Zoo Veterinarians website: http://
www.aazv.org/secure/cagpathologysurvey.htm.
132
L. Munson / Theriogenology 66 (2006) 126–134
8. Summary
Progestins continue to be the most available and
affordable contraceptive for females, but serious side
effects resulting in permanent infertility or even death,
are common. The PZP vaccines used to date do not
appear to be effective, and the adjuvants may not be well
tolerated in cats. However, prospects for safe and
effective felid contraception for both females and males
have improved over the last decade as a result of clinical
trials testing GnRH analogs, LH-R vaccines, and
bisdiamines. Commercial availability of these nonprogestin methods continues to be a problem, because
manufacturing and marketing costs can rarely be
covered by the limited veterinary market. However,
smaller companies, such as ZooPharm and Peptech, are
responding to this important need for safer, effective
felid contraceptives.
Clinical trials testing the efficacy and safety of nonsteroid contraceptives for male cats, such as indenopyridines, should be a high priority for research. Clinical
trials assessing contraceptive safety of new bioengineered contraceptives should also be conducted in cats as
these drugs become available. The domestic cat serves as
a valuable model for wild felids in any contraceptive trial.
Surveillance for immediate as well as long-term adverse
effects of currently available contraceptives also should
be conducted at the national/international level to
determine contraceptive safety through off-label use
outside of a formal clinical trial. Information from
prospective clinical trials and from surveillance of safety
and efficacy in individual animals prescribed contraceptives can then be combined to provide the needed
knowledge to determine benefits/risks for contraceptive
use in domestic, feral, zoo, and wild felids.
Acknowledgements
The author thanks Rob Mason, Rebecca Pappendick,
Lisa Harrenstien, Jennifer Stokes, Carol Kazensky, Anne
Acton, Lisa Chassy, Lorna Bolton, Michelle Hawkins,
Tara Harrison, Anneke Moresco and Virginia Doucett for
excellent assistance at The Contraceptive Health
Surveillance Center for Animals. The author wishes to
recognize Ulie Seal as an inspiration to everyone
interested and involved in wildlife contraception.
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