I've heard that English Mastiffs aren't precisely the same as Neopolitan Mastiffs, though of course there are similarities. (Drool, among other things.
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I've heard that Neos are livelier, less aloof, and more aggressive guarders, but every Neo that I have met seemed very much like an English--a big baby, but definitely a good watch dog.
All the Great Danes I've met have been sweethearts--but they too can be good watchdogs.
I could be wrong, but on the whole it sounds like Danes do not live *quite* as long as mastiffs.
I've always heard that mastiffs live 8-10 years. Our first lived 10 1/2.
Our second only 7 1/2.
Our third is going strong at 3 and 1/2.
One quality that both Neos and Danes share: Danes can come in the beautiful blue-grey color that so many Neos have. I've seen mahogany Neos, they are gorgeous too.