The English Mastiff is a large breed of dog which descended from the ancient Alaunt and Molosser. This breed of dog goes up more than 300 pounds. I am sure you really need lots of pet supplements and dog food for something like this. Take the English mastiff bitch owned by Tom Scott of East Lake, Leicestershire, England for example. It set the world record as the heaviest living dog with a weight of 286 pounds last August 18, 1999. But in 1989 The Old English Mastiff owned by Chris Eraclides of London named Zorba weighted 343 pounds.