I’ve not long come across a case of a middle-aged dog that had suddenly become unaccustomedly grumpy and started snapping at its poor owners.
This was uncharacteristic, as it had no previous history of behavioural problems. There were no other obvious clinical signs – perhaps it had become lazy of late, but there was nothing to put your finger on.
I recalled having attended a CPD event a while before when the speaker mentioned hypothyroidism leading to aggression. I thought this was worth a punt, and low and behold it had a very high thyroid-stimulating hormone level and very low thyroxine result. Our friend is now on thyroid supplementation and is much happier, although at the time of writing some two to three months into therapy, it was not completely better.
So, it may be worthwhile considering a blood profile when presented with signs of aggression in middle-aged dogs.