I think it depends on what breed the dog is. For example it might be more informative to list a large teacup Chihuahua`s weight in grams. That would tell you the large Chihuahua`s weight relative to other large Chihuahuas. On the other hand a large Old English Mastiff`s weight given to the closest kilogram would tell you plenty about the dog`s size compared to other large dogs of that same breed.
However I think the correct answer is kilograms.