Approaches to Non-Surgical Fertility Control
What is non-surgical sterilization for cats and dogs?
We’re often asked this question. The answer: there is no single approach to controlling reproduction without surgery. The field is wildly diverse, complex, and (in our humble opinion!) fascinating. The brain, pituitary gland, and gonads are all vital to reproduction; this yields multiple potential approaches for temporary or permanent infertility in male and female cats and dogs.
In some cases, mammalian physiology makes it possible for a single approach to effectively suppress fertility across multiple species, dogs and cats included, and/or in both males and females. In other cases, a particular approach is possible for only one species or one sex.
The Hypothalamic-Pituitary-Gonadal Axis
The picture to the right shows a simplified version of the hypothalamic–pituitary–gonadal axis in both sexes. Interfering with any part of the axis will affect reproductive capacity. This diagram shows how different approaches target different parts of this system.
Key Approaches
Gene transfer and gene delivery
In a gene transfer approach, a gene (DNA in the form of a plasmid) is introduced into cells, usually by a one-time IM injection of an engineered viral vector, which carries the DNA to the cells of various organs such as the liver and muscle. The gene does not get integrated into the cell's DNA, but sits within the cell and is translated into a protein, and this protein is continuously produced over the life of that cell. Depending on the gene delivered, a variety of proteins may be expressed that can suppress animal reproduction, thus resulting in long-term or lifetime sterility. The large number of genes involved in reproduction provide many possible targets.
Sex steroids
Think of “The Pill” for dogs and cats. Use of sex steroid hormones, the most common of which are progestins (synthetic progesterone), for fertility control has been explored in both species. Available in oral or injectable forms, and effective at preventing pregnancy, they must be given on an ongoing basis and carry some significant risks, particularly with extended use.
GnRH agonists and antagonists
Gonadotropin-releasing hormone (GnRH) agonists and antagonists target this key hormone for reproduction. GnRH agonists, commonly administered by implant, are further developed than antagonists for dogs and cats.
Gonad-Focused approaches
Sometimes referred to as “chemical castration,” this involves injecting a chemical agent into a male dog or cat’s testis, epididymis, or vas deferens to cause permanent azoospermia and sterility. To date, there are no viable non-surgical options directly targeting the female ovaries which are, obviously, less accessible being inside the body.
Immunological approaches
These approaches use a vaccine to stimulate the body’s immune system to produce antibodies to key proteins involved in reproduction.
| Options | GnRH Agonists | Sex Steroids | Gonad-Focused | Immunological |
|---|---|---|---|---|
| Species | Cat Dog | Cat Dog | Dog | Dog |
| Administration | Subcutaneous implant | Oral (tablets) Subcutanous or intramuscular injection | Intratesticular injection | Subcutaneous injection |
| Duration | Temporary | Temporary | Permanent/ potentially permanent | Temporary |
| Agent | Deslorelin acetate* | Megestrol acetate* Medroxyprogesterone acetate* Proligestrone* | Zinc gluconate neutralized with arginine** Calcium chloride*** | Recombinant protein |
| Brand | Suprelorin® | Depo-Provera® Delvosteron® | Zeuterin™ Neutersol® EsterilSol™ | Egalitte® |
* Available; varies by species and country ** No longer available *** Experimental
Species: Cat, Dog
Sex: Male and prepubertal female
Administration: Subcutaneous implant
Duration: Temporary; 6+ months (4.7 mg) and 12+ months (9.4 mg)
Agent: Deslorelin acetate*
Brand: Suprelorin®*
Considerations for use:
Suprelorin®*:
Initial hormone spike.
Can be used continuously.
Approved in male dogs and cats, and pre-pubertal female dogs (note: sex and species approval is country specific).
Occasionally prescribed off-label in adult female dogs and cats.
Note that use in adult females can cause temporary induction of estrus, followed by infertility, and use in adult female dogs over 5 years of age can cause uterine disease.
Species: Cat, Dog
Sex: Female only
Administration: Oral (tablets/powder), subcutaneous or intramuscular injection
Duration: Temporary; duration varies by species and agent
Agent: Megestrol acetate (MA)*, medroxyprogesterone acetate*, proligestone*
Brand: Megace®*, Depo-Provera®*, Delvosteron®*, FeralstatTM**
Considerations for Use:
General:
Should only be used with close veterinary oversight and should not be used for extended periods of time.
Potential for serious adverse effects such as: uterine proliferation, diabetes mellitus, decreased immune function, and mammary tumors.
Requires frequent dosing for oral treatment.
Species: Cat, Dog
Sex: Male only
Administration: Intratesticular injection
Duration: Permanent (Zeuterin) /potentially permanent (CaCl2)
Agent: Zinc gluconate neutralized with arginine**, calcium chloride (CaCl2)***
Brand: ZeuterinTM **, NeutersolTM**, EsterilSolTM**
Considerations for Use:
General:
Level of testosterone reduction is variable with calcium chloride.
If not administered properly, potential for adverse site reactions, including abscesses and tissue necrosis.
Use of calcium chloride should be considered experimental.
Zeuterin is not currently manufactured and is unavailable for purchase or use.
Species: Dog
Sex: Male and Female
Administration: Subcutaneous injection
Duration: Temporary; ~5 months - 1 year
Agent: Recombinant protein
Brand: Egalitte®
Considerations for Use:
Egalitte*:
Currently only available in Chile.
Requires two initial injections (3-4 weeks apart) and yearly booster injections.
Initial reports indicate likelihood for ability to use continuously.
Must be administered during diestrus stage of reproductive cycle (for females), which requires additional testing by a veterinarian to determine.
New product, information still being learned
* Available; varies by species and country ** No longer available *** Experimental
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Species: Cat, Dog
Administration: Subcutaneous implant
Duration: Temporary
Agent: Deslorelin acetate*
Brand: Suprelorin®
Click for more information.
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Species: Cat, Dog
Administration: Oral (tablets), subcutaneous or intramuscular injection
Duration: Temporary
Agent: Megestrol acetate*, medroxyprogesterone acetate*, proligestrone*
Brand: Depo-Provera®, Delvosteron®
Click for more information.
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* Available; varies by species and country ** No longer available *** Experimental