Data says the notion is nuts
Does castration really make male dogs less dangerous?
The historical record says it does not.
That castration should make male dogs safer has been presumed since 1923, when the American Veterinary Medical Association first approved the safety of the surgical procedure for dogs. But the presumption has been surprisingly little studied, and what research data there is turns out to be at best ambiguous.
Writers about animal husbandry have recognized since Biblical times that castrating bulls to produce oxen and castrating stallions to produce geldings yields more tractable animals, better suited to most work, much less likely to injure the humans handling them.
Castrating human males to make eunuchs has similar results, though eunuch warriors have often won distinction, including the 15th century Chinese Muslim admiral Zheng He.
“Much of our experience with the effects of castration on behavior has been with livestock––cattle and horses. We do see substantial impacts in behavior. We also see this with cats,” summarized then-American SPCA science advisor Steve Zawistowski at the 2013 Alliance for Contraception in Cats & Dogs conference in Portland, Oregon.
But among dogs, Zawistowski added, “There have been studies by James Serpell and Anthony L. Podberscek, and by Illana R. Reisner, among others, showing that castration has a limited and variable impact on aggression.”
Zawistowski, who served 25 years with the ASPCA, has since retired.
Castration & attacks
K.A. Gershman, Jeffrey J. Sacks, and J.C. Wright reported in the journal Pediatrics in 1994, based on 1991 Denver dog bite data, that non-castrated male dogs are about 2.6 times more likely to bite people than the average dog. As the data was collected three years after Denver banned pit bulls, it cannot be extrapolated to pit bull behavior.
The Gershman, Sacks, and Wright finding has been widely amplified. But if non-castrated male dogs were 2.6 times more likely to bite at all times, in all places, dog bites in the U.S. should have steeply dropped since 1960, when the first surveys of sterilization frequency found that barely 1% of the U.S. dog population had been sterilized.
The historical record
In 1960 there were about 611,000 dog bites resulting in medical treatment, according to the first Centers for Disease Control estimate of the incidence of severe dog bites. There had been an average of under one dog attack fatality per year in the U.S. during the preceding three decades. The U.S. dog population was about half of the present number. Under 1% were pit bulls, but pit bulls had killed nine people in 30 years. Dobermans, then the most feared breed, had killed two people.
The hypothesis that castration makes dogs safer seemed to hold up for about 25 years. By 1985 about half of all dogs in the U.S. were sterilized, according to several different surveys, while the CDC found that dog bites requiring medical treatment had dropped to 586,000. But pit bulls were up to 2% of the U.S. dog population, and fatal dog attacks had increased to an average of 10 per year, including five fatalities per year inflicted by pit bulls.
From 0.5 dead per year in 1960 to 40+ now
More than 70% of the dogs in the U.S. were sterilized by 1991, and more than 80% today, exclusive of pit bulls, among whom the sterilization rate is circa 25% or lower. Pit bulls are now 5.6% of the U.S. dog population. (See 2018 dog breed survey: at least 41% of U.S. pit bull population are seeking homes.) Dog bites requiring medical treatment have increased to more than 4.5 million per year. Fatalities in the present decade are averaging nearly 40 per year, with an average of 30 inflicted by pit bulls. (See 57 dog attack deaths & 645 disfigurements in 2017, led by pit bulls.)
About two-thirds of the fatal and disfiguring dog attacks occurring in the U.S. during the past 33 years have been by pit bulls. The low rate of sterilization among pit bulls contributes mightily to the repeated finding that the majority of fatal and disfiguring dog attacks are by non-castrated male dogs. But about two-thirds of the fatal and disfiguring attacks by castrated male dogs are also by pit bulls.
Particularly telling is that dogs rehomed from animal shelters and rescues have killed 49 people from 2007 to mid-2018, all of the dogs either castrated or spayed, and all having passed behavioral screening. Among those dogs have been 37 pit bulls, four Rottweilers, three bull mastiffs, and one Akita, one boxer, one “golden retriever” who may have been a pit bull mix, one husky, and one dog of unknown breed.
Excluding pit bulls from the data removes any distortion due to pit bull proliferation. But even with pit bulls excluded, today’s mostly sterilized dogs appear to be about a third more likely to inflict a bite requiring medical treatment than the unsterilized dogs of 1960.
Little research on effects in normal dogs
“There is little research into the effect of neutering in pet dogs who do not have a pre-existing behavioural problem,” summarized N. C. Guy and six corresponding authors in the September 2001 edition of Applied Animal Behaviour Science. This is still true.
Among the studies that have been done, J.C. Neilson, R.A. Eckstein, and Benjamin L. Hart of the Veterinary Medical Teaching Hospital at the University of California at Davis reported in 1997 that about a third of 57 mature male dogs were less aggressive toward family members after castration. The other two-thirds were not.
“Castration was most effective in altering objectionable urine making, mounting, and roaming. Castration may be effective in decreasing aggression in some dogs,” Neilson, Eckstein, and Hart reported, “but fewer than a third can be expected to have marked improvement.”
Hart and S.G. Hopkins had reported 21 years earlier that castrating dogs did not appear to reduce either territorial or fear-related aggression.
Serpell and Podberscek in 1996 reported a significant positive association between neutering and aggression among English cocker spaniels, though the effect was strongest in females.
“Many of the breeds showing up as most aggressive in these studies were small breeds,” observed Zawistowski. “If castration reduces testosterone levels, this might result in reduced confidence and perhaps a reason for fear biting.
“I think that attacks by larger dogs, whether they are pit bulls, Rottweilers, or whatever, appear more like predatory attacks than dog-versus-dog social aggression,” Zawistowski added, “based on reports that I have read for court cases, and videos of such attacks.”
As making male dogs safer appeared to be a persuasive argument for castration, contributing to population control, the presumed behavioral benefits of castration were little questioned by the humane community, but may have undercut enthusiasm for injectible chemosterilants, such as Zeuterin, and indeed for any non-surgical sterilization method which does not reduce testosterone production.
“While surgical neutering virtually eliminates testosterone, Zeuterin lowers testosterone by about half,” acknowledged the web site of Ark Sciences, the Zeuterin distributor, when the product was reintroduced in 2014. “Based on feedback from animal caretakers and dog owners, zinc neutering has suppressed mating behaviors and calmed the dogs down. The U.S. Food & Drug Administration allows the following statement about zinc gluconate: Like surgical castration, it may or may not suppress mating behaviors.”
The Zeuterin formulation was originally marketed by Addison Labs in 2003 as Neutersol. According to Ark Sciences, Addison Labs “overestimated the growth in demand and created too much inventory. The excess inventory expired in two years and the manufacturer went unpaid, shutting down production.”
Ark Sciences acquired the Neutersol distribution rights in 2011, reintroduced the product as Esterilsol for international markets, and brought it back to the U.S. in 2013 as Zeuterin––but it was off the market again by early 2016.
The most promising rival to Zeuterin, among injectable chemosterilants, is calcium chloride injection––a very cheap, simple technique that has rapidly gained favor abroad for population control use, and is now under study in the U.S. for dog population control by organizations including Spay FIRST! of Oklahoma.
Spay FIRST! in recent years has focused on preventing the severe testicular swelling that has often followed use of all injectable chemosterilants. Keeping ANIMALS 24-7 apprised of progress, Spay FIRST! founder Ruth Steinberger is optimistic that some changes in the formulation of the injected solution and the technique of injecting it will eliminate the problems, without reducing the efficacy of calcium chloride in reducing testosterone and sperm production.
Becoming interested in the potential of calcium chloride as a chemosterilant in 2007, the California-based Parsemus Foundation has funded studies by animal reproduction specialist Raffaella Leoci of University Bari Aldo Moro in Italy.
Leoci’s work suggested that calcium chloride may have a significant advantage over other currently available chemosterilants, apart from cost, because it more effectively reduced testosterone production by the injected animal. Indeed, Leoci claimed, calcium chloride injections may cut testosterone levels twice as much as the 40-to-50% drop claimed for Zeuterin.
This may prevent some behavioral problems that are common causes for dogs being surrendered to animal shelters, including inappropriate mounting and marking.
But Leoci, the Parsemus Foundation, Spay First!, and Planned Pethood Plus have all been cautious, if hopeful, about equating reduced testosterone with making dogs less dangerous.
“ACC&D stands for the Alliance for Contraception in Cats & Dogs, not the Alliance for Behavioral Modification in Cats & Dogs,” Zawistowski reminded the ACC&D conference on June 22, 2013.
“If we allow ourselves to become sidetracked by concerns about behavioral effects, as legitimate as these concerns are, we may tend to lose our focus on the primary issue that ACC&D exists to address, which is to reduce the numbers of the animals whose behavior concerns us. If nothing else, reducing the numbers of these animals on the streets and coming into our shelters will reduce the numbers of animals whose behavior raises public concern and may require our efforts to modify.”
Continued Zawistowski, who holds a Ph.D. in behavioral genetics and is on the ACC&D board of directors, “Inasmuch as we know that dogs are morphologically and physiologically the most varied of any mammal species, especially those dogs whose physiognomy has been the most altered by humans through selective breeding for specific traits, it would not be surprising if they showed variable responses to different drugs,” including zinc gluconate, calcium chloride, and other chemosterilants for male dogs.
Specifically, Zawistowki said, dogs bred to display predatory behavior may have a different response to either castration or chemosterilants than dogs whose “aggressive” behavior has origins in social conduct.
“In any species in which this has been examined, including dogs, fish, and poultry, enhanced aggression is among the easiest traits to breed for. This is due to the fact that high levels of aggression are usually not adaptive, and there is latent genetic variation available. The alternative––the ability to select for tameness––is also true,” Zawistowski said.
Charles Vreeland says
Can you give the citation for the 80% altered percentage nationally? Thanks! Just want to provide some explanation for the reduction in intake many shelters have been experiencing over the last five to six years.
Joyce Briggs says
Thank you, Merritt, for bringing attention to the important topic of castration and behavior in the context of new alternatives for non-surgically neutering dogs. As pet owners, veterinarians, and shelters get new chances to consider alternatives, it is important that new fertility control options are judged against realistic rather than mythic standards for behavior change with castration.
I appreciate you quoting Dr. Stephen Zawistowski, a well-regarded expert in this area. I’d like to emphasize that there are many different subcategories of dog “behavior,” and even many subcategories of dog “aggression,” whether that aggression is directed toward humans (the focus of this article) or other animals. This is but one reason why it is—and will continue to be—difficult to establish a correlation between sterilization, levels of sex hormones, and aggressive behavior.
As you point out, research on this topic, particularly based on objective analysis rather than owner reports, is limited. Given the difficulty in measuring behavior differences between intact and castrated dogs, the difference in behavior between dogs treated with injectable Zeuterin or a calcium chloride-ethanol solution, which both result in partial reduction of testosterone, is likely to be very difficult to compare (indeed no studies so far have) and variable dog to dog.
The relatively new option for dog sterilization by the FDA approved commercialized product, Zeuterin, and the compounded formula made with calcium chloride prompt many questions by pet owners, shelters and veterinarians. ACC&D’s resources on these are comprehensive and science-based; we have no financial interest in any product. They can be found at http://www.acc-d.org. I encourage your readers to learn more about these new methods for extending humane population control to more dogs.
President, Alliance for Contraception in Cats & Dogs
Merritt Clifton says
We agree with Joyce Briggs that “It is important that new fertility control options are judged against realistic rather than mythic standards for behavior change with castration.” Her next statement, however, that “There are many different subcategories of dog ‘behavior,’ and even many subcategories of dog ‘aggression,’ whether that aggression is directed toward humans (the focus of this article) or other animals,” is both true in gist and widely misinterpreted. Advocates for pit bulls and other dogs of fighting ancestry commonly misstate this as an assertion that canine aggression toward humans is a behavior entirely different from canine aggression toward other animals, or specifically other dogs, and that therefore aggressive behavior toward humans can somehow be bred or trained out of dogs of fighting ancestry, even if “animal-aggressive” or “dog-aggressive” behavior continues.
This erroneous belief has had tragic consequences for well over 100 years, promulgated by, among others, professional dogfighter John P. Colby, of Newburyport, who produced his first pit bull litter in 1889. Soon thereafter Colby began selling pit bull pups he deemed unfit for fighting as pets, promoted with photos of the pit bulls with small children. The Boston Globe on December 29, 1906 reported that police shot one of Colby’s dogs, who mauled a boy while a girl escaped. Undaunted, Colby continued to promote his culls as pets. On February 2, 1909 the Globe described how one of Colby’s dogs killed Colby’s two-year-old nephew, Bert Colby Leadbetter. Even this incident, however, did not stop Colby, who went on to cofound the Staffordshire Club of America, and to the end of his life continued to promote the pernicious myth that “dog aggression” or “animal aggression” is somehow different from aggression toward humans. Colby thereby laid the foundation for pit bull advocacy that continues to this day.
Literature produced by dog behaviorists and legislation drafted by public policy makers has historically treated ordinary dog bites and those of more severe consequence as a continuum produced by “aggressive” dog behavior. Dog training, dog guardian education, and animal control ordinances have consequently focused on preventing or restraining “aggression” in dogs, without understanding that “aggression” in non-fighting breeds may be much less the issue than the capacity for doing extreme damage in any biting incident, and that the “aggression” of fighting breeds might more accurately be described as a lack of inhibition against attacking any other species with intent to kill, regardless of the size, species, or behavior of the target.
The capacity for doing extreme damage is coupled in dogs of fighting lineage, e.g. pit bulls, bull mastiffs, Rottweilers, and their mixes, with the tendency among breeds produced to fight to explode from calm to all-out attack for an obvious reason, in that the dog who hesitates in a fight to the death will soon be killed.
As Joyce Briggs mentioned in passing, at least 15 common dog behaviors may be considered aggressive, and may result in biting, but most are rarely involved in fatal and disfiguring attacks on either other dogs or other species, including humans.
Among these “aggressive” behaviors are play-chasing; the air-biting & growling of two dogs who are just becoming acquainted; enthusiastically greeting a person by leaping up on the person or putting paws up; trying to steal food; barking, even when the barking is just a friendly hello; fear-biting; defense of food; growling at a perceived territorial intruder; irritability at being suddenly awakened (mostly seen in older dogs); assertion of dominance; and response to pain, either acute or chronic.
Defense of pups by a female dog was identified in early Dog Bite Prevention Week literature (1955-1961) as the most single common cause of bites, very distantly followed by rabid behavior.
Studies published from the mid-1930s into the 1960s consistently identified female dogs as most likely to bite.
Fatal and disfiguring attacks were then so rare, occurring at the rate of less than one non-rabid fatality per year 1851-1971, that no one even tried to study them before the late 1960s. Yet during most of that time the national dog sterilization rate was zero, rising from about 1% to about 10% after 1960.
Neither defense of pups nor rabies is commonly seen now in either the U.S. or Canada, where the rate of sterilization of female dogs reached circa 70% in the early 1990s, while canine rabies was eradicated from the U.S. by the early 21st century.
Predatory behavior, more than classically aggressive behavior, appears to be commonly involved in fatal and disfiguring attacks by wolf-like dogs, such as wolf hybrids, huskies, Akitas, Malamutes, German shepherds, and their mixes.
But by far and away the aggressive behavior most often involved in fatal and disfiguring dog attacks in the U.S. and Canada today, whether the victims are human or animal, is the characteristic behavior of pit bulls and other breeds of fighting ancestry, associated with hair-trigger reactivity to stimulus and the capability of doing catastrophic harm in a first-ever biting incident.
Tony Solesky says
As usual an excellent read
Ruth Steinberger says
Merritt and Beth as usual thank you for a great piece and for noting Spay FIRST’s extensive work in this field.
Neutering male dogs doesn’t eliminate all poor behaviors, or make a “pet” of a particular dog, any more than castrating a horse eliminates the possibility that the horse may kick someone. Genetics, training and lifestyle all come into play. But so does testosterone.
First and foremost, castrated male dogs don’t seek females in estrus (most ultimately ignore the scent), and that eliminates or reduces many problems including the annoyance of dogs that even destroy walls to get loose and roam, some to be found miles from home and some never to be found at all. Neutering absolutely reduces the likelihood of a dog lifting a leg on furniture. If the dog was a rescue dog, having nice behavior may help him remain rescued. Undesirable behavior will not.
But all of those points presume that a dog will be around furniture or see the inside of a house, or be cared for in some way. Globally most will not.
When a female street dog goes into estrus and there are a large pack of males attracted to and following her around (as a pack), fighting with each other, the entire presence is intimidating to people nearby. Add in a perceived or real threat of rabies (and other factors) and the historic response has been lethal culling. Spaying the female is obviously ideal. But if it is significantly cheaper and easier, eliminating the precursor to this scene has value to the dogs.
The combination of circumstances that befall street dogs, and end up with people wanting to eliminate them, are why Spay FIRST! has continued our hands on research to determine an effective, safe and easily duplicated process for the application of calcium chloride.
The overwhelming number of street dogs are in developing nations. Calcium chloride is a compounded product made of two ingredients (calcium chloride and generally ethanol) that are too common to be patented, it can provide global availability for non surgical neutering at a very low cost. No one owns calcium chloride, so everyone owns calcium chloride, so to speak. Veterinarians can use it virtually everywhere, and for simply the cost of the ingredients.
While pit bulls are skewing data and our national conversation, there is a difference in the expectations of behavior between a castrated vs uncastrated male dog. I know this from the ones at my house. Giving homeless dogs the best chance they can have to simply “get along” is the value of neutering or using a non-surgical neutering product for male dogs.