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FactCheck: Are restricted dog breeds inherently more dangerous than all the rest?

TheJournal.ie’s FactCheck does some digging into a perennial debate that has flared up in Ireland in recent weeks.

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ONE OF THE most controversial news stories of the last fortnight has been around the erection of signs in public parks in Co Meath, listing the 10 breeds of dog deemed “restricted” in Ireland.

On Sunday 8 May, Meath County Councillor Alan Tobin wrote on Facebook that he welcomed the signs, and the restriction of the breeds. He added:

As a dog owner I’m absolutely delighted that signs I’ve asked for, with pictures, showing the dangerous breeds of dogs have been erected over the past week. It still amazes me that some people think these dogs are ideal family pets.

His comments provoked outrage and some support, and the substance of his claim – that restricted dog breeds are “dangerous” and not appropriate family pets – was hotly disputed.

One reader, Jana in Dublin 15, got in touch to ask us to find out the truth.

Remember, if you see an assertion that doesn’t sound right, email factcheck@thejournal.ie.

Claim: Restricted dog breeds are inherently more dangerous than non-restricted dog breeds
Verdict: Mostly False.

  • There is mixed scientific evidence on whether breeds restricted in Ireland are disproportionately likely to bite, and in the case of some breeds, virtually no evidence
  • Virtually no evidence that their behaviour is genetically ingrained and inherent to them (rather than socially and environmentally determined)
  • No evidence to show that restricted dog breeds are physically more capable or apt than other large breeds to inflict serious damage when they do bite, although there is no scientific research either way in this specific area, and so this is potentially subject to change.

The Facts

13173787_1094453353945648_6739222994702736572_n Source: Alan Tobin via Facebook

Eleven dog breeds were first restricted in Ireland under the 1991 Control of Dogs Regulations, signed by then Environment Minister Pádraig Flynn.

The rules came in the wake of public debate following a May 1991 attack by an American pitbull on six-year-old girl Rucksana Khan in the English city of Bradford.

The 1998 Control of Dogs Regulations designated 10 breeds restricted, meaning they must be muzzled, kept on a leash and wear a collar bearing their owner’s name and contact information, at all times in any public place.

That action removed the bulldog from the list of restricted breeds, but retained the restriction on the following breeds:

American Pit Bull Terrier; Bull Mastiff; Doberman Pinscher; English Bull Terrier; German Shepherd (Alsatian); Japanese Akita; Japanese Tosa; Rhodesian Ridgeback; Rottweiler; Staffordshire Bull Terrier.

This remains in place.

Are those dogs more dangerous than others?

Dog bite statistics which specify dog breeds are extremely limited in Ireland.

There is only one paper published in a peer-reviewed journal which measures it – by Edmund O’Sullivan from the Veterinary Department of Cork City Council (and others) in 2008.

He studied 234 dog bite incidents in Cork in 2004-2005, and the dogs found to have bitten their owners or unfamiliar adults were (with restricted dogs in italics):

  • Collie (42 incidents), Terrier breeds (31), Cocker/springer spaniel (22), Jack Russell (20), German shepherd (20), crossbreed dogs (12), golden retriever (6), daschund (5).

However, the authors do not attribute that prevalence of biting to the dog’s breed itself. But rather, simply, to how many of them there were around.

The most popular dog breeds in Cork at that time were (in descending order, with restricted dogs in italics):

  • Collie, terrier breeds, labrador, Jack Russell, cocker/springer spaniel and crossbreeds.

And these were the breeds with the highest bite rate (taking into account their actual prevalence in the locality):

  • Papillon, Brittany spaniel, Kerry blue terrier, Newfoundland, weimaraner and Pekingese.

The dog breeds with the lowest bite rate:

  • Cavalier King Charles, beagle, bichon frise, Staffordshire bull terrier, samoyed and Pyrenean mountain dog.

The paper concluded that:

The data…indicates that the breeds frequently reported for biting were popular breeds, rather than breeds with a greater propensity to bite.

This finding appears to reflect a lot of international scientific research on the subject.

Police raids on dangerous dogs Source: PA WIRE

A 2008 study in the journal Applied Animal Behaviour Science summarised the three main reasons why larger dog breeds, often considered “dangerous”, are over-represented in research on dog bites and aggression (and therefore in the public consciousness):

  • “Most dog bites go unreported unless medical attention is sought (which may be more likely with larger breeds that have the ability to inflict more serious injury)”
  • “The total number of dogs of a given breed in the local community is seldom known, so the degree to which that breed is over-represented among reported dog bites is usually undetermined”
  • “In many cases the breed of dog involved cannot be verified”

That study used an animal behaviour questionnaire to measure the aggression levels of 5,312 dogs from 36 different breeds. With breeds restricted in Ireland italicised, here’s what it found:

  • Most aggressive towards (human) strangers: Dachshunds, Chihuahuas, Doberman Pinschers, Rottweilers, Yorkshire Terriers and Poodles
  • Most aggressive towards their owners: Basset Hound, Beagle, Chihuahua, American Cocker Spaniel, Dachshund, English Springer Spaniel and Jack Russell Terrier (none of which are restricted in Ireland)
  • Most aggressive towards other dogsAkita, Boxer, Australian Cattle Dog, German Shepherd, Pit Bull, Chihuahua, Dachshund, English Springer Spaniel, Jack Russell Terrier and West Highland White Terrier

Short-haired-Dachshund A short-haired daschund, the breed found most aggressive towards strangers in one study. Source: Wikimedia

There is plenty of research which identified a higher prevalence of biting and aggression among breeds often considered dangerous, although most do not necessarily attribute that behaviour to breed itself.

A Dutch study from 2010 took into account the popularity of various breeds, and found that these were the top six most bite-prone breeds (in descending order):

  • Rottweiler, Doberman, German shepherd, Belgian shepherd, Bouvier des Flandres (also known as the Flanders cattle dog), Jack Russell, Golden retriever, Labrador retriever, Yorkshire terrier, Maltese.

However, the authors called for policies that encouraged education (particularly of children, who are especially vulnerable to facial bites due to their stature), and opposed breed-based strategies to avoid injury.

1991 study in the French city of Lyon found that 10 veterinary clinics reported 102 dog bites and scratches during 1987 and 1988.

Half of those (51) came from German shepherds.

However, the study does not list any other dog breeds, or state what the overall prevalence of German shepherds was in that area at that time. So very little can be concluded from it, in that respect.

A 1994 study found 178 dogs reported for biting for the first time in Denver, Colorado during 1991. A further 178 dogs with no biting history were randomly chosen from the same neighbourhoods, in order to give a representative sample of dog breeds in the locality.

denver Source: John Wright/Journal of the American Academy of Pediatrics

Five out of 12 breeds were more likely to have bitten than not to have bitten:

  • German Shepherd, Chow Chow, Collie, Akita, and Doberman Pinscher.

However, only the findings for German Shepherds (restricted in Ireland) and Chow Chows (not restricted) were statistically significant.

One important disclaimer about this study is that pit bulls were not included, as they were banned entirely from the city of Denver at the time.

A 2006 study from Austria looked at dog bites on children over a 10-year period and came up with the following “risk index”, which took into account each breed’s popularity in the locality of the study.

austriastudy Source: Johannes Schalamon/American Academy of Pediatrics

The top two breeds (German shepherd and Doberman) are restricted in Ireland.

Spitz is a group of breeds with shared ancestry, which includes some huskies, the Akita (restricted in Ireland), the chow chow, and many others.

Out of the top 18 breeds specified, only three are restricted by law in Ireland, although those three are all in the top 10.

And conversely, of the 10 breeds restricted in Ireland, only three featured among the 18 most bite-prone breeds in this study.

Even among the studies we reviewed which found that certain breeds were more bite-prone than others (taking account of their popularity), only one identified the dog’s breed as the primary contributing factor to aggressive behaviour.

Kennel Club's Safe and Sound Quality Kitemark Resource launch A school pupil in England during a course on interacting safely with dogs. Source: GEOFF CADDICK/PA

Almost all emphasised the greater importance of proper dog training and education for owners and children on awareness of signs that a dog was agitated, territorial or fearful.

Not neutering dogs was also found to be a significant, preventable contributing factor for bites, in several studies.

A major 2009 study in the journal of Plastic and Reconstructive Surgery reviewed five years’ worth of dog bite admissions to the Children’s Hospital of Philadelphia.

It found that the breeds most commonly identified in the biting incidents were:

  • Pit bull (137 bite victims), rottweiler (24), pit bull mix (13), German shepherd (10), German shepherd mix (9), Akita (8), cocker spaniel (8), rottweiler mix (4).

Four out of five of these breeds (pit bull, rottweiler, Akita, German shepherd) are restricted in Ireland.

However, this study (again) did not reference those figures to the overall popularity of each breed within the community being studied.

So it has limited value in finding out how bite-prone each breed is. Also, the single largest group of dogs (282 bite victims) found by the study were those whose breed could not be determined.

Australian research in 1997 controlled for population and produced this “representation ratio”, similar to the “risk index” described earlier.

australia Source: Peter Thompson/The Medical Journal of Australia

It found that the five most bite-prone breeds were the Doberman, German shepherd, rottweiler, bull terrier, and blue/red heeler (also known as the Australian cattle dog).

Three of those five are restricted in Ireland.

However, those 154 dog bite incidents only represent 43% of the total examined by the authors.

In 57% of cases, the breed of the dog involved could not be determined, a very serious problem common to many of the studies we reviewed.

Which breed is which?

Outlawing Pet Sales Source: Associated Press

A major piece of research in this regard is a 2013 study in the Journal of the American Veterinary Medical Association, which used an uncommonly wide range of official sources (police, coroner’s and animal control reports) to examine the causes of 256 dog bite fatalities in the US. It found that the most common factors were:

  • Absence of an able-bodied person to intervene
  • Incidental or no familiar relationship of victims with dogs
  • Owner failure to neuter dogs
  • Compromised ability of victims to interact appropriately with dogs
  • Dogs kept isolated from regular positive human interactions
  • Owners’ prior mismanagement of dogs
  • Owners’ history of abuse or neglect of dogs

The authors concluded that “Most DBRFs [dog bite-related fatalities] were characterised by coincident, preventable factors; breed was not one of these.”

It also found that a valid determination of a dog’s breed was made in only 17.6% of cases.

Even among studies which found dogs typically regarded as “dangerous” to be most bite-prone, many we reviewed pointed out the difficulty of accurately and reliably determining a particular dog’s breed.

This difficulty is based on the fact that breed determination is usually done by sight and measurement, rather than DNA testing, and because mixed breeding within individual dogs is so prevalent.

This has significant implications for ascertaining whether some breeds are in fact more dangerous than others, and since breed is the sole criterion in “breed-specific legislation”, this knowledge gap alone should bring into question the scientific validity of restrictions like the 1998 Control of Dogs Regulations.

Are restricted breeds more dangerous “by their nature”?

Dog stock A chihuahua biting a man's finger on the London underground. Source: PA

A major Swedish study in 2005 tested 31 breeds for several different temperamental characteristics. Here were the top 10 breeds (in descending order) in each category, with Irish-restricted ones in italics.

  • Aggressiveness:  Belgian Malinois, American Staffordshire Terrier, Parson Russell terrier, Great Swiss Mountain Dog, Australian Shepherd, Labrador Retriever, Dalmatian, Giant Schnauzer, Rottweiler, Rhodesian Ridgeback
  • Playfulness: Belgian Malinois, Flat-coated retriever, German shepherd, Rottweiler, Border collie, Labrador retriever, Giant schnauzer, Dobermann pinscher, Nova Scotia duck tolling retriever, Parson Russell terrier
  • Curiosity/Fearlessness: Labrador retriever, Parson Russell terrier, Flat-coated retriever, Belgian Malinois, American Staffordshire terrier, Rottweiler, Great Swiss Mountain Dog, German shepherd, Irish soft-coated wheaten terrier, boxer
  • Sociability: Flat-coated retriever, boxer, Labrador retriever, American Staffordshire terrier, golden retriever, border collie,  Nova Scotia duck tolling retriever, rottweiler, Australian kelpie, giant schnauzer

The study concluded that the characteristics present in the breeds were not a result of their historical origins, but of recent artificial selection (that is, selective breeding for specific purposes).

A 2006 paper applied a series of behavioural tests, in particular surrounding aggression, to 25,726 dogs from dozens of breeds.

The results were analysed on the basis of breed groups like sporting, terriers, toy breeds, hounds, etc…

Unfortunately we can’t extract the performance of any one breed from their grouping, except American pit bull terriers (APBT), who were treated as a separate group, but these are the results.

behaviourtest Source: Scot Dowd

It’s notable that the hound dog and toy dog groupings had the worst pass rate. Only one out of the 46 breeds in those two groupings is restricted in Ireland – the Rhodesian Ridgeback.

The American pit bull, pit bull group and working group (which contained five breeds restricted in Ireland) all scored significantly better than the toy and hound dog groups. The author concludes:

The current study has statistically shown, based on a defined temperament test, that the classification of dog breeds and dog breed types (breed groups), with respect to their aggressiveness toward humans is not supported scientifically.
The temperaments of animals are fundamentally and universally acknowledged to be influenced by age, sex, early socialisation, early nutrition, training, health and genetics, while [breed-specific legislation] only takes one of these factors into account.

It would appear that the genetic origins and original functions of different modern dog breeds are far less associated with their temperament and behaviour than are their recently-developed functions.

For example, some breeds restricted by law are often trained, bred (and crossbred) for the purpose of fighting, protection, and intimidation. Without proper education (especially for children) on “reading the signs” of canine territoriality, not interrupting meals, and so on, the risk of biting increases.

But it’s important to note that even studies which found restricted dogs more likely to bite did not attribute these differences solely, or even primarily, to breed (with one exception).

And the differences between breeds appears to be attributable to their current function (developed over a tiny number of generations, relative to their overall history) as guard dogs and fighting dogs, rather than any ancient, ingrained, unchangeable characteristics.

Do restricted dog breeds bite harder than others?

Pets Dogs Bites An animal behaviourist examines a Rottweiler-Husky mix. Source: Associated Press

This is a huge question. Media reports of attacks by “dangerous dogs” (especially those containing graphic photos) definitely feed into the widespread acceptance that even if certain breeds are not disproportionately predisposed to violence, when they do attack, the damage they inflict can be devastating.

This is certainly true of restricted dog breeds, but it is also true of non-restricted dog breeds.

All dogs have the capacity to bite and inflict injury, and small, non-restricted breed dogs have inflicted fatal injuries, especially on children.

Common sense would indicate that the relatively large size and strength of restricted dog breeds means their attacks have a greater capacity to inflict more serious injuries.

However, there is actually relatively little scientific research available that compares bite force across different dog breeds, and therefore would support that view of restricted dogs.

Two studies from 2008 and 2009 gathered data on the body weight and skull shapes (length and width) of 20 domestic dog breeds, and used electrodes applied to anaesthetised dogs to stimulate their maximum biting force.

In short, the results were as you might expect – the bigger the dog, the harder it bit.

Any other research in this specific area has so far also focused on size, rather than breed.

A 2009 paper published in the Journal of American Veterinary Medicine explained the unusual absence of scientific research in this specific area.

Bite force (and pressure, which is force per unit area) is technically difficult to measure in dogs. In the contrived environment of an experimental situation, it is presently almost impossible to recreate the arousal that drives a dog’s biting behaviour during a real-life attack…

It concluded:

Beyond reaffirming the obvious finding that larger dogs have the potential to inflict greater damage than smaller dogs, discussion of bite force associated with particular breeds seems to have minimal clinical relevance and may only inflame and polarise the discussion.

Conclusion

Pit Bull Police Dog An officer in New York trains a two and a half year old pit bull as a police dog. Source: Associated Press

  • Firstly, there is mixed scientific evidence on whether the 10 breeds restricted by law in Ireland are disproportionately prone to aggression and biting.

In fact, we could find no substantive mention at all of one of them (the Japanese Tosa) among the scientific evidence we reviewed.

The only reference to the Bullmastiff that we found was a paper which found it was among the least aggressive of 20 popular breeds studied.

The Rhodesian Ridgeback was found by one paper to be among the 10 most aggressive breeds (along with eight breeds not restricted in Ireland), and by another to be less aggressive than dozens of non-restricted breeds.

The third and final reference to it was in a study which found that a Rhodesian Ridgeback had been involved in one fatality in the 20-year period between 1979 and 1998 in the US – far fewer than non-restricted breeds like the collie, Labrador retriever, and Saint Bernard.

  • Secondly, accurately determining a biting dog’s breed is widely accepted as not done, more often than it is done.

By definition, this is a severe blow to the claim that certain, named breeds are more dangerous than others, and therefore undermines the scientific validity of any legislation based solely on breed.

  • Thirdly, there is no evidence to support the idea that a breed’s behaviour or temperament is determined by an ancient, ingrained “nature”.

Rather, a breed’s stereotypical characteristics are largely determined by very recent human choices about selective breeding (which, by definition, can be reversed by different human choices).

And an individual dog’s behaviour and actions (or more pointedly, reactions) are also determined by its training, socialisation, diet, and environment.

  • Finally, there is no scientific research to support the claim that dogs restricted under Irish law have a greater physical capacity to inflict damage, than other large dogs.

However, there has been no research whatsoever comparing bite force across different breeds, so this part of the ongoing argument will have to be watched carefully, and could well change in the future.

Based on the scientific evidence we’ve reviewed, though, the claim that dog breeds restricted under Irish law are inherently more dangerous than non-restricted ones, is Mostly False.

Send your FactCheck requests to factcheck@thejournal.ie

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About the author:

Dan MacGuill

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