Why do dogs walk around in a circle before lying down?

Circling is innate behaviour

The most probable reason why many dogs circle before they lie down is that their ancestors did so in the wild. You just can’t beat a good nights sleep and simply by circling  around in an area of grass would create a more level, softer surface for lying on. If the area was covered in snow or leaves, circling would similarly soften and level the spot.

The behavioural effects of castrating male dogs (Neutering)

Having your dog neutered is not a decision that you should take lightly, after all there is no going back once the deed is done! Before proceeding you should consider the effects that castration may have on your dog’s behaviour.

The castration of male dogs will stop the production of the hormone testosterone. This might be beneficial when treating unwanted behaviours that are more likely in males than in females. Urine marking, roaming away from home to track down bitches in heat, inappropriate sexual behaviour, and inter-male competitive behaviour. In contrast, and contrary to popular belief, castration does not “calm a dog down”, since excitable and unruly behaviours are seldom influenced by testosterone.