I have read that the dog brain weights a 1/125 of the total mass of the animal, with slight variations on this figure for the biggest or smallest breeds.
Most dogs breeds have roughly the same intelligence level, but how can it be so if the mass of the brain varies so much among breeds?
I mean, I have a small Chihuahua and her brain must weight around 20 grams, while the brain of a Great Dane weights more or less 450 grams.
How can they be more or less as smart if the big dog brain it's at least 22 times more massive than the one of the small dog?

Is it a matter of proportion? I'm assuming the individual weight and size of the neurons to be the same, so in absolute numbers, my Chihuahua has much less neurons than the Great Dane. How can she, with less neurons, be as smart, rich and complex as any other dog?

Great question! Take a look at the link below, it is in many ways similar to the question is a whale smarter than a human or a parrot vs a deer. Bottom line it's not the size or weight of the brain that is important, rather the number of neurons and synapses with the resulting complexity. That is I assume the same in small and big dogs.

http://www.smithsonianmag.com/science-n … 27/?page=1