Standard spay and neuter surgery can have negative impacts on a dog’s health. What are some alternatives options?
In the United States, broad scale pet sterilization has been advocated to decrease pet overpopulation and euthanasia rates at shelters. This practice has become standard, with shelter animals being sterilized before adoption and most pet owners spaying or neutering their animals even if not adopted from a shelter. The decrease in the number of pets entering shelters (estimated at six to eight million currently, down from 13 million in 1973), and the resulting decrease in euthanasia rates, are cited as successful outcomes of spay/neuter programs.1,2 However, removing an animal’s reproductive organs can have adverse effects as well as benefits. This article looks at some alternatives to spay and neuter surgery.
Pros and cons of gonadectomy
In the US, sterilization involves removal of the reproductive organs (gonadectomy), usually through ovariohysterectomy (spay) of females and orchiectomy (castration) of males. These procedures eliminate the hormones produced by these organs.
While gonadectomy makes it impossible for the pet to reproduce, what other impacts does a lack of sex hormones have on the pet? Research projects to answer this question first evaluated the difference between early and later gonadectomy, usually supporting the early sterilization practice of sheltered pets.3,4 More recently, research has broadened to compare large numbers of gonadectomized dogs with intact dogs.5,6
This area of study is relatively new, but the research indicates that gonadectomy confers a mixture of benefits and adverse effects, depending on age at neutering, breed and sex.7 Eliminating sex hormones has the positive effect of reducing mammary, ovarian and testicular cancers, pyometra, perineal and inguinal hernias, prostatitis, benign prostatic hyperplasia, prostatic cysts and squamous metaplasia of the prostate. Intact dogs have a higher incidence of infectious disease and sterilized dogs have higher cancer rates, with the latter often reported as having longer lifespans.8 On the other hand, gonadectomized dogs have been reported to have a higher incidence of obesity, urinary incontinence, urinary calculi, atopic dermatitis, autoimmune hemolytic anemia, hypoadrenocorticism, diabetes mellitus, hypothyroidism, immune-mediated thrombocytopenia, inflammatory bowel disease, hip dysplasia, cranial cruciate ligament rupture, aggressive and fearful behavior, cognitive dysfunction syndrome, prostate adenocarcinoma and transitional cell adenocarcinoma.6,9-12 Musculoskeletal issues may be especially significant for large breed dogs gonadectomized before they have finished growing, as bone physeal closure is delayed.
A significant contributor to the negative health impacts of removing the gonads in dogs is that the natural hormone feedback mechanisms become unregulated. Normally, the pituitary gland releases luteinizing hormone (LH), which then stimulates the production of steroid hormones from the gonads. Without the gonads, there is no feedback signal to reduce production so LH concentrations remain very high for the remainder of the dog’s life. Receptors for LH are present in the urinary tract, skin, thyroid, blood vessels, ligaments, bone, synovium, immune cells and brain.12 Elevated LH concentrations resulting in activation of these receptors may predispose gonadectomized dogs to developing the health problems listed previously.
Alternative options to traditional spay/neuter
Responsible pet ownership
It is interesting to note that while gonadectomy is viewed as the standard in the US, it is relatively uncommon in other regions of the world. In Norway and Sweden, for example, there are virtually no stray dogs and neutering is very uncommon, usually only allowable due to health concerns.13
To avoid unwanted pregnancies, responsible pet owners of intact dogs must take special precautions. Females go into heat for a few days once or twice a year and need to be confined in an area without access to intact males. Male dogs should not be allowed to roam freely, as they are incredibly persistent in reaching a female in heat.
Other issues to consider include females bleeding while in heat; behavior changes that may be triggered by changing hormones; the logistics of having both male and female intact dogs in the same house; and health monitoring for diseases of the reproductive organs. Responsible dog owners are expected to manage these issues.
Not all pet owners are ready to keep an intact dog and guarantee that no unwanted pregnancies will occur. Luckily, there are options that will ensure a dog is incapable of reproducing while keeping his/her natural gonadal hormones to protect his/her health.
Females: A hormone-sparing option that sterilizes a female dog involves conducting a hysterectomy (also called ovary-sparing spay or partial spay) by removing the uterus and leaving the ovaries intact. It is important to remove all the uterus to ensure that stump pyometra does not occur.
After the procedure, the female dog is sterile and bleeding is eliminated. The female will still go into heat due to the influence of hormones produced by her ovaries, possibly showing behavioral changes around this time.
Ovarian cancer is often cited as an argument for removing ovaries — but ovarian cancer is rare, and the small risk does not outweigh the health benefits of preserving hormones. However, the dog should be monitored for mammary tumors after middle age. An owner can do this when he/she rubs the dog’s tummy. These tumors are usually benign but should be removed promptly. Veterinarians may wish to establish/offer mammary examination as part of annual wellness checkups for senior dogs.
Tubal ligation has also been practiced in dogs, but pyometra remains an issue, as well as bleeding during heat, making ovary-sparing spay a better option.
Males: For male dogs, a vasectomy sterilizes while sparing testosterone. The procedure involves severing or ligating the vas deferens, the duct that transports sperm. The procedure is quick, less invasive than castration, and not difficult for veterinarians to master.
What are the downsides of testicular preservation? Leaving the testicles and hormones intact means that testicular cancer, perianal gland tumor, and enlarged prostate may occur — but if they arise later in life, they are typically treated via castration. In such a case, the dog’s health still benefitted from years of natural hormones prior to castration. Also, prostate enlargement can now be treated non-invasively with finasteride (Proscar®, Merck) or by using pulsed electromagnetic therapy.14 Hormones will also influence the male dog’s behavior and interest in females in heat, a complex issue discussed below.
Other experimental approaches: The epididymis is the sperm maturation and storage area, making it an ideal target for hormone-sparing sterilization procedures. Injection of a necrotizing agent, such as calcium chloride in alcohol, can effectively disrupt the ability to produce sperm. Leoci and colleagues reported success with this non-surgical approach using ultrasound guidance (personal communication, 2018). The dogs retained normal hormone profiles, yet were sterile. Other options, such as epididymal ligation15 or therapeutic ultrasound,16 are promising approaches that require more refinement for use in companion animals.
Parsemus.org offers information on hormone-sparing options, including extensive online training material for veterinarians on ovary-sparing spay.
An ethical dilemma
Questioning whether gonadectomy is really in the best interest of the dog has raised the hackles of many veterinarians and organizations who work hard to sterilize animals in the US to reduce pet overpopulation. Interpretation of research results has been hotly debated, with many arguing that differences in the long-term health of gonadectomized dogs are negligible, and others arguing that they are serious enough to reconsider the wisdom of widespread spay/neuter programs.
The issue represents a common ethical dilemma – is the welfare of the population more important than the welfare of the individual? In other words, is the positive impact of gonadectomy on reducing pet overpopulation more important than the possible negative impact on an individual dog’s long-term health and welfare?
Stepping back from the debate, it is not surprising that the loss of natural gonadal hormones has significant health implications for the dog. As veterinary practitioners, it makes sense for us to understand and discuss the pros and cons of gonadectomy with clients when decisions about sterilization are made. This individualized approach is supported by the American College of Theriogenologists.10
This doesn’t require locking into adversarial positions or giving up spay/neuter. Fortunately, there are a number of alternative methodologies to consider, including methods for sterilizing dogs while maintaining hormone levels. The next step is to evaluate the different options available to the dog owner or adopter, and determine the best option for the particular dog and situation.
A note on behavior
Gonadal hormones can have behavioral effects, and hormone-sparing options are appealing to dog owners who do not want changes in behavior (e.g., for performance or hunting dogs). On the other hand, many express the concern that leaving dogs with natural hormone levels will produce undesirable behaviors. This sentiment is common in animal welfare and rescue/shelter communities, with the rationale that dogs may display more inter-male aggression, urine marking, mounting and roaming, which may result in owners abandoning or returning their pets and thus increasing shelter populations.
We are beginning to understand that behavior is under the influence of a number of psychological and physical stimuli, and that no simple straight-line relationship between hormones and undesirable behaviors exists. For example, eliminating testosterone may not make a dog less aggressive. In fact, a recent large survey reported that gonadectomized dogs did not differ from intact dogs in terms of aggression directed toward familiar people or pets, and they actually showed higher levels of aggression toward strangers.5 Dog aggression is a main reason for relinquishment to shelters17 and neutered male dogs were more often surrendered for such behavioral reasons.18 Gonadectomized dogs may also develop more anxiety and fear, and show more cognitive decline than intact dogs.19,20
The dog’s age, breed, personality and environment will impact his/her behavior. When choosing a hormone-sparing method, if a dog evidences behavioral issues later, traditional spay or neuter can then be considered. Keep in mind that castration of adult male dogs may decrease reproductive-related behaviors (urine marking, mounting and roaming) but impacts on other behaviors are variable.21
As our understanding of the long-term health consequences of gonadectomy in dogs grows, the demand for alternative options increases. Unfortunately, the supply of practitioners experienced in alternatives has not met the demand. In most veterinary schools in the US, students are not taught how to do hysterectomy or vasectomy, and the number of veterinarians making these options available is small. At the 2017 AVMA conference, 81 veterinarians were surveyed about the use of nontraditional sterilization methods. Only 7.4% percent reported performing hysterectomies or vasectomies in dogs, whereas 73.4% reported discussing long-term health risks of traditional spay and neuter with dog owners prior to surgery.
Parsemus Foundation is doing its part to encourage education, dialogue and communication with pet owners and practitioners. Their website offers information on hormone-sparing options, including extensive online training material for veterinarians on ovary-sparing spay. They also maintain a list of veterinarians who offer alternatives to traditional spay/neuter; many have reported receiving referrals from this service. Parsemus Foundation envisions a win-win future, when veterinarians offering choices are sought out by dog owners and adopters who want the most appropriate method of sterilization for their individual pets.
More vets are needed to turn this innovative trend into an impactful movement. To join the growing list of clinics that offer safer alternatives to traditional spay and neuter, contact firstname.lastname@example.org.
For individuals seeking a veterinarian to perform procedures beyond surgical spay or neuter, view a list of providers here.
The authors thank Elaine Lissner, founder and trustee of Parsemus Foundation, for her review of an earlier version of this paper, and advocacy for innovative and alternative methods of pet sterilization.
1Humane Society of the United States. “Pets by the numbers”. No date ; downloaded 6/27/18 from: humanesociety.org/issues/pet_overpopulation/facts/pet_ownership_statistics.html.
2Marsh P. “Replacing myth with math: Using evidence-based programs to eradicate shelter overpopulation”. 2010; Town and Country Reprographics, Inc., Concord, New Hampshire.
3Howe LM1, Slater MR, Boothe HW, Hobson HP, Holcom JL, Spann AC. “Long-term outcome of gonadectomy performed at an early age or traditional age in dogs”. JAVMA 2001;218:217-21.
4Spain CV, Scarlett JM, Houpt KA. “Long-term risks and benefits of early-age gonadectomy in dogs”. J Am Vet Med Assoc 2004;224:380-7.
5Farhoody P, Mallawaarachchi I, Tarwater PM, Serpell JA, Duffy DL, Zink C. “Aggression toward familiar people, strangers, and conspecifics in gonadectomized and intact dogs”. Front Vet Sci 2018;5:1-13.
6Sundburg CR, Belanger JM, Bannasch DL, Famula TR, Oberbauer AM. “Gonadectomy effects on the risk of immune disorders in the dog: a retrospective study”. BMC Vet Res 2016;12:278.
7Kustritz MVR. “Determining the optimal age for gonadectomy of dogs and cats”. J Am Vet Med Assoc 2007;231:1665-1675.
8Hoffman JM, Creevy KE, Promislow DE. “Reproductive capability is associated with lifespan and cause of death in companion dogs”. PLoS One 2013;8(4):e61082.
9Reichler IM. “Gonadectomy in cats and dogs: a review of risks and benefits”. Reprod Domest Anim 2007;44(Suppl. 2):29-35.
10Society for Theriogenology, Board of Directors, and the American College of Theriogenology. “Basis for Position on Mandatory Spay-Neuter in the Canine and Feline”. 2013; downloaded 6/27/18 from: c.ymcdn.com/sites/www.therio.org/resource/resmgr/docs/spay-neuter_basis.pdf.
11 Zink, C. “Spay neuter considerations to maximize health”. IVC Journal 2017;Feb. 6, 2017.
12Zwida K, Kutzler MA. “Non-reproductive long-term health complications of gonad removal in dogs as well as possible causal relationships with post-gonadectomy elevated luteinizing hormone (LH) concentrations”. J Etiol Anim Health 2016;1(1):1-11, article number JEAH-1-002.
13Sallander M, Hedhammar Å, Rundgren M, Lindber JE. “Demographic data of a population of insured Swedish dogs measured in a questionnaire study”. Acta Vet Scand 2001;42:71-80.
14Leoci R, Aiudi G, Silvestre F, Lissner E, Lacalandra GM. “Effect of pulsed electromagnetic field therapy on prostate volume and vascularity in the treatment of benign prostatic hyperplasia: a pilot study in a canine model”. Prostate 2014;74:1132-41.
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16Leoci R, Aiudi G, Silvestre F, Lissner EA, Marino F, Lacalandra GM. “Therapeutic ultrasound as a potential male dog contraceptive: Determination of the most effective application protocol”. Reprod Dom Anim 2015;50:712–718.
17Weiss E, Gramann S, Spain CV, Slater S. “Goodbye to a good friend: An exploration of the re-homing of cats and dogs in the US”. Open J Anim Sci 2015;5:435-456.
18Salman MD, Hutchison J, Ruch-Gallie R. “Behavioral reasons for relinquishment of dogs and cats to 12 shelters”. J Appl Anim Welfare Sci 2000;3:93–106.
19Hart BL. “Effect of gonadectomy on subsequent development of age-related cognitive impairment in dogs”. J Am Vet Med Assoc 2001;219:51-6.
20Kim HH, Yeon SC, Houpt KA, Lee HC, Chang HH, Lee HJ. “Effects of ovariohysterectomy on reactivity in German Shepherd dogs”. Vet J. 2006;172:154-9.
21Neilson JC, Eckstein RA, Hart BL. “Effects of castration on problem behaviors in male dogs with reference to age and duration of behavior”. J Am Vet Med Assoc 1997;211:180-2.
Dr. Linda Brent is a scientist and organizational leader with expertise in non-human primate behavior, animal welfare, non-profit management, project management, preclinical research, grant writing and scientific writing. She is a founder of Chimp Haven, Inc. – a sanctuary for chimpanzees retired from medical research – and served as its President and Director from 2002 to 2012. Dr. Brent is Executive Director for Parsemus Foundation, which funds innovative and neglected medical advancements.