Aggressive dogs represent a serious risk to human health, tragically causing fatalities in some cases. The development of aggression can also impact on the welfare of dogs themselves, often resulting in the break-down of the human-pet bond, euthanasia or relinquishment. Research into factors which influence the development of aggression is therefore very important. One type of research commonly used is epidemiology. This type of study looks at populations of dogs with the aim of identifying common factors which might help explain the development of aggression. A number of approaches have been used in epidemiological research, varying both in the types of population studied and the factors measured. These different approaches add to the understanding of the problem and give us valuable new insights. For example, a number of studies have investigated the occurrence of dog bites by looking at information on hospital admissions^1,2. Interesting recent research has also looked at potentially preventable husbandry factors in a series of fatal dog bite cases in the USA³ (nicely summarised and discussed in these blogs^4,5). This type of study is crucial in informing us about the specific circumstances in which the most serious aggressive incidences occur.

Other populations of dogs that have been studied include cases referred to specialist behaviour clinics^6,7 or dogs relinquished to shelters⁸. These studies highlight the impact on dog owners, with aggression being the most common reason for people to seek specialist help, and an important reason for abandonment. The great value of these types of study is that they can include a detailed evaluation of the specific circumstances or contexts in which aggression occurs.

A further epidemiological approach is to use more general populations, such as owners visiting first opinion veterinary practices⁸, or surveys of dog owners in the general population^9,10. These populations provide information about factors which may be important across a broader range of dogs or dog owners. We took this approach in two recently published papers investigating aggression in UK dogs. Our interest was to examine potential risk factors for dogs showing any aggression either to other dogs¹¹ or people¹². Dog owners were asked to fill in a questionnaire about one of their dogs. We asked them whether their dog barked, lunged, growled or bit in a number of situations. These were: when meeting other dogs when out for walks; with other dogs within a household; when meeting unfamiliar people when out of the house; when meeting unfamiliar people entering the house, or when with family members. We were interested in how common it was for aggression to occur in these different situations, and whether the same dogs showed aggression in multiple situations. We also went on to look at potential risk factors for aggression by comparing the characteristics of dogs which showed aggression with those which did not – and I’ll come back to that part in a later blog post.

How common is aggression in UK dogs?

Questionnaires were distributed to just under 15,000 dog owners in a range of different situations: veterinary practices, dog shows or similar events, agricultural or horse shows, directly to dog walkers, pet stores, and a range of other locations. Just under 4000 questionnaires were returned to us completed (thank you so much lovely dog owners!), and these gave us an idea of the proportion of dogs showing aggression. The most common context in which aggression occurred was towards other dogs on walks (22% of respondents)¹¹, and the least common was aggression to family members (3%)¹² – numbers and percentages for all the situations we investigated are shown in the table below.

Situation in which aggression occurred	Number	Percentage
Towards family members12	126	3.2
Towards unfamiliar people entering the house12	258	6.6
Towards unfamiliar people when outside the house12	197	5.1
Towards other dogs when out on walks11	871	22.4
Towards other dogs in the household11	326	8.4

Although we distributed questionnaires as widely as possible, it is important to interpret these numbers with a bit of caution, because the owners who participated were not necessarily representative of the total UK dog population. For example, those not registered with a vet or who lived in remote areas were unlikely to have seen the survey. However, these numbers give us an idea about the relative prevalence of different types of aggression – and particularly highlight that aggression between dogs is a worryingly common problem, something that those working in dog behaviour are probably well aware.

Do individual dogs show aggression in multiple situations?

There is a common perception that aggression is a fixed characteristic of particular dogs – people often think that dogs are either ‘safe family dogs’ or ‘nasty / vicious dogs’ based on traits inherent to the breed or the dog itself. However, our studies highlighted that dogs were rarely aggressive in more than one situation: co-occurrence of aggression between contexts was remarkably low. This tends to suggest that dogs learn to show aggression in particular situations through learning. Hence, whilst some characteristics of personality may be important in the development of aggression, the unique learning experiences of each individual dog is also likely to be very important.

This has two important implications: dog owners and members of the public need to be aware that any dog could potentially show aggression, even where it has never done so in other situations. Secondly, dogs which have shown aggression in one situation are not necessarily ‘dangerous’ when in other contexts – an important factor in the assessment of animals, for example in re-homing centres.

References

1. De Keuster, T., Lamoureux, J., Kahn, A., 2006. Epidemiology of dog bites: a Belgian experience of canine behaviour and public health concerns. Vet. J. 172, 482-487.
2. Morgan, M., Palmer, J., 2007. Dog bites. Br. Med. J. 334, 413-417.
3. Patronek, G.J., Sacks, J.J., Delise, K.M., Cleary, D.V. and Marder, A.R. (2013). Co-occurrence of potentially preventable factors in 256 dog bite-related fatalities in the United States (2000-2009). J Am Vet Med Assoc. 2013 Dec 15; 243(12):1726-36. doi: 10.2460/javma.243.12.1726.
4. National Canine Research Council (2013). Potentially Preventable Husbandry Factors Co-occur in Most Dog Bite-Related Fatalities
5. Cattet, J. (2013) New study sheds light on serious to fatal dog bites
6. Bamberger, M., Houpt, K.A. (2006). Signalment factors, comorbidity, and trends in behavior diagnoses in dogs: 1,644 cases (1991-2001). J. Am. Vet. Med. Assoc. 229, 1591-1601.
7. Fatjo, J., Amat, M., Mariotti, V.M., de la Torre, J.L.R., Manteca, X., 2007. Analysis of 1040 cases of canine aggression in a referral practice in Spain. Journal of Veterinary Behavior-Clinical Applications and Research 2, 158-165
8. Guy, N.C., Luescher, U.A., Dohoo, S.E., Spangler, E., Miller, J.B., Dohoo, I.R., Bate, L.A., 2001. Risk factors for dog bites to owners in a general veterinary caseload. Appl. Anim. Behav. Sci. 74, 29-42
9. O’Sullivan, E.N., Jones, B.R., O’Sullivan, K., Hanlon, A.J., 2008. The management and behavioural history of 100 dogs reported for biting a person. Appl. Anim. Behav. Sci. 114, 149-158.
10. Hsu, Y., Sun, L., 2010. Factors associated with aggressive responses in pet dogs. Appl. Anim. Behav. Sci. 123, 108-123.
11. Casey, R.A., Loftus, B., Bolster, C., Richards, G.J. and Blackwell, E.J. (2012). Inter-dog aggression in a UK owner survey: prevalence, co-occurrence in different contexts and risk factors. doi: 10.1136/vr.100997
12. Casey, R.A., Loftus, B., Bolster, C., Richards, G.J. and Blackwell, E.J. (2013). Human directed aggression in domestic dogs (Canis familiaris): occurrence in different contexts and risk factors. doi: http://dx.doi.org/10.1016/j.applanim.2013.12.003