This is a great question, and is not the easiest to answer because there are a lot of reasons, so we need to break it down into bits so that you can understand where YOUR dog is coming from. If you’d prefer to watch a video of this blog, here’s a link, otherwise carry on reading!
So firstly, let’s look at the question:
Why is my dog aggressive towards other dogs?
Most often we’re thinking about behaviour on walks, but it can apply in the home as well – and it’s also relevant when we look at why our dogs may be reactive to humans as well.
So here’s the thing: There’a a circuit in our dog’s brain and when that circuit is switched on we see aggressive behaviour. (Berthoud, H.-R. and Münzberg, H. 2011). This part of the brain is super ancient and is just worried about survival – you’ve probably heard all about fight or flight and it’s all about this. However, dogs are a social species and before domestication their ancestors lived in family groups. Since domestication we’ve done hundreds of generations of selective breeding , so switching this on is really difficult. Everything about our dogs is geared towards resolving conflict, so you don’t need to stress about switching this circuit on, but it is helpful to understand it.
So what does cause that circuit to switch on?
Think about the bucket analogy. Everything that is happening to our dogs is fulling the bucket – good things and bad. Big things like pain, or something scary, fill the bucket a lot, small things do too, and good things like exciting play time fill the bucket too. We can look at filling the bucket as being the thing that could switch on the circuit.
The bucket is just an analogy for various chemicals in the brain such as serotonin, dopamine and cortisol. And here’s the thing! Geeky studies found that the level of blood cortisol was significantly higher in dogs showing aggression than those that weren’t and that the reverse was the case for the levels of serotonin (Çakiroǧlu et al., 2007). What does this mean? That these chemicals in the brain are what switches on that circuit!
Now, we know that for some dogs, switching the circuit on is harder than for others.
And there are a number of reasons for that.
1. Genetic Predisposition
Genetics are HUGE. Where one or both of the parents shows fearfulness / aggression, then the puppies are far more likely to – simple! (Mikkola et al., 2021) – amongst others. Breeding dogs for temperament rather than looks would be a great idea, but that’s a whole other topic.
2. Previous Experience
Traumatic experiences can greatly increase the reactive responsive of our dogs to others – if our dog has had a bad experience with a dog in the past it will impact their reactions in the future.
3. Health problems
Again, HUGE. Imagine you’re in pain, you don’t really want anyone you aren’t totally comfortable with near you and maybe not even them!
4. Lack of, or inappropriate socialisation
Dogs know how to interact with other dogs, however, lack of experience of novel dogs, experiences etc means that new dogs can be super scary. Unfortunately, all to often “socialisation” is taken to mean unrestricted play with as many dogs as possible which can lead to bad experiences (see point 2!).
5. Cues from the other dog (or person!)
Our dogs’ communication is really complex and may be subtle but they are experts and reading both each other’s faces and bodies and human faces (Racca et al., 2009).
Come on! Answer the question!
Why is my dog aggressive towards some dogs but not others on walks?! Or even, why is my dog aggressive to one particular dog?
Now we know why dogs over react to other dogs at all. Why some dogs not others.
Firstly, let’s consider that circuit which is needing switching on – or the bucket.
On a walk, things are happening to your dog and around your dog all the time, so it may be that these experience are adding up. In actual fact, their bucket may still be filled up with things that have happened over the last few days! Remember that this includes things like pain, itchiness, other dogs they have encountered etc. The dog who walks past some dogs before the bucket overflows has a bigger bucket than the one which reacts straight away.
Secondly, let’s look at the dog’s prior experiences, combined with the fact that we know that dogs recognise other dog’s faces (Racca et al., 2009). Let’s say that your dog had a bad experience with a big, white, fluffy dog. That can mean that big, white, fluffy dogs can be a problem in the future, or even big dogs, or white dogs, or fluffy dogs. Or all 3!
Thirdly, what about the cues from the other dog. Or it can be a lack of cues! Black dogs and short faced dogs can be difficult for other dogs to read as their facial expressions are less clear. Or it can be that the cues from the other dog are shouting “back off!”, which in turn is bucket filling for our dogs. If it’s one particular dog your dog struggles with, there could be a history of “back off!” body language – and we know that our dogs can recognise individual other dogs.
Finaly, don’t forget the cues your dog is picking up from the person (or people with the other dog!) Children, for example, can be hugely bucket filling for our dogs as they are so unpredictable.
What can we do about it?
Tip 1: Manage your dog’s bucket. Control what’s going into it, work on making it bigger and make sure there’s a big hole in the bottom so that your dog knows how to calm down more quickly.
Tip 2: Work on growing your dog’s confidence! Make sure that the experiences they have are varied and positive and that you avoid putting them in fearful situations like the plague.
Tip 3: Learn about dog body language here
For further help book a free 30 min call.
References
Berthoud, H.-R. and Münzberg, H. (2011) ‘The lateral hypothalamus as integrator of metabolic and environmental needs: From electrical self-stimulation to opto-genetics’, Physiology & Behavior, 104(1), pp. 29–39. doi:10.1016/j.physbeh.2011.04.051. Çakiroǧlu, D. et al. (2007) ‘Relationship between the serum concentrations of serotonin and lipids and aggression in dogs’, Veterinary Record, 161(2), pp. 59–61. doi:10.1136/vr.161.2.59. Mikkola, S. et al. (2021) ‘Aggressive behaviour is affected by demographic, environmental and behavioural factors in Purebred Dogs’, Scientific Reports, 11(1). doi:10.1038/s41598-021-88793-5. Racca, A. et al. (2009) ‘Discrimination of human and dog faces and inversion responses in domestic dogs (canis familiaris)’, Animal Cognition, 13(3), pp. 525–533. doi:10.1007/s10071-009-0303-3.