Traditionally, castration (removal of the testes) was used to prevent male animals from reproducing. The neutering of male dogs is a common example. More recently, options for male sterilization have expanded and are being used for specific animals and purposes.
An interesting article by scientists at the University of Illinois at Urbana-Champaign and published in Frontiers in Veterinary Science reviews the history of castration, its use in production animals, pets, and wildlife, and the efforts to find alternative methods to sterilize male animals. In some cases, these alternatives are better than castration!
Humans have been practicing castration on animals for centuries
Castration has been conducted to reduce male sex hormone-induced behavior and breeding in domestic animals since ancient times. Herds of sheep and goats, used for milk or fiber, were castrated as long ago as 7000 BC. Due to its simple and effective application, castration has been widely used in food production animals since this time. For example, over 600 million pigs are castrated annually to reduce aggression and “boar-taint” (the odor and taste in pork from intact males).
Castration practices were later applied to domesticated pet species and zoo animals. To control pet overpopulation, spay and neuter for dogs and cats became widespread in many parts of the world and were often considered part of responsible pet ownership.
How the male reproductive system works
The article, “Male animal sterilization: history, current practices, and potential methods for replacing castration,” provides a review of the male reproductive system including the possible targets for sterilization. The system includes two brain organs — the hypothalamus and the pituitary gland — and the gonads (testes in males). Hormones produced in one area either stimulate or inhibit the secretion of a hormone in the other organ via positive and negative feedback loops.
- The brain: The hypothalamus produces kisspeptin, which triggers gonadotropin-releasing hormone (GnRH). It travels to the anterior pituitary and stimulates the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
- The gonads: LH and FSH stimulate the male testes to produce sex steroids, peptide hormones, and spermatozoa. The testosterone produced provides “negative feedback” to the hypothalamus and pituitary — telling those structures to turn down production and thereby regulating the system.
This regulatory system maintains the required levels of hormones for the stimulation of testicular function. Targets for sterilization and contraception occur throughout the system.
Beyond castration: new methods of male sterilization and contraception
Traditionally, surgical castration has been the go-to method for managing unwanted behaviors and controlling pet populations.
“It’s amazing that for 9000 years castration has remained the primary method for sterilization of male pets and livestock, with essentially no new technology having been seriously adopted,” said lead author Rex Hess, Ph.D., Professor Emeritus at the College of Veterinary Medicine at the University of Illinois. “This review was written to raise awareness about the need for more scientific effort to develop alternatives.”
The authors note that male sterilization research in animals has gone through several phases starting with surgical castration, which is still common today. Cutting or crushing the spermatic cord was later practiced in farm animals such as sheep and goats.
Since the 1960s, chemical sterilization has been studied in many mammals. The toxic effects of the chemicals and side effects have made chemical sterilization challenging to use in domestic animals, but several chemical sterilization products have been produced for male rodents. More promising has been the injection of chemicals into the testes or associated tissues, which can produce a local response without a systemic effect.
The latest alternatives to male animal castration involve hormone treatment, immune-castration, and gene therapy.
A focus on dogs: Surgical sterilization without affecting hormones
Castration or neutering has been the most common method to sterilize dogs. Removal of the testes has the benefit of eliminating or reducing diseases associated with this organ or those influenced by testosterone, such as enlarged prostate. Behaviors such as roaming and urine marking are also reduced in castrated dogs. However, research has revealed evidence for significant risks associated with castration including increased incidence of cancers, orthopedic conditions, and endocrine diseases. For more details, see our webpage on the impact of spay and neuter on health.
To maintain normal hormone levels, dogs can be sterilized without removing the testes. A vasectomy, in which the tubes carrying sperm (vasa deferentia) are cut, has become a common gonad-sparing sterilization method in dogs to address the health concerns of castration. A plug to block the vasa deferentia or ligation of the testicular artery will also result in sterility.
Non-surgical alternatives to castration for dogs
Interest in exploring alternatives to castration of dogs has grown over time, leading veterinarians and scientists to test other methods of sterilization.
- Chemical Castration: Injectable agents (such as calcium chloride dihydrate) can induce permanent infertility when targeting the testes, epididymis, and/or vas deferens. These methods aim to provide a less invasive alternative while ensuring long-term or permanent effects like traditional castration.
- Hormonal Contraception: Drugs like deslorelin implants (Suprelorin®) and other GnRH analogs can suppress testosterone production, which can help manage behaviors related to testosterone. The effect is temporary contraception, with new implants required at regular intervals.
- Immunological Castration: Another promising method is immunological castration, which works by stimulating the immune system to produce antibodies against the specific target proteins. This method could prevent male sexual behavior and may also be reversible depending on the treatment protocol used. More research on pets is needed.
- Gene Editing: This technology can inactivate any of the genes related to the male reproductive system. It has been used in pigs using CRISPR/Cas9 technology, but much more research will be needed to determine the best targets and deal with ethical issues of genetic manipulation of the reproductive system.
These alternatives offer various benefits, including potentially fewer side effects and less recovery time compared to surgical options. They also provide options for pet owners who may be hesitant to pursue surgery for various reasons, such as anesthetic risk, or in resource-restricted locations. The development and adoption of these methods could significantly impact how we manage canine reproductive health and behavior in the future.
To stay abreast of non-surgical methods of contraception or sterilization in dogs, visit the Alliance for Contraception in Cats and Dogs.
