Originally Posted by Toms777
That would be pit bulls and mastiffs.
Possibly. But that would generally imply that they used both at the same time.
To take it to a different subject:
"Chicken or veal is used to make parmigiana" means that people make it with either.
"Chicken and veal is used to make parmigiana" means that people use both together in the dish.
And, of course, there is the appositive phrase, which is probably what threw the OP off:
Germans Shepherds, or GSDs, are often used by the police.
But that would properly need the commas, which might not be as apparent when someone is talking.
But at the end of the day, pits and mastiffs are different breeds.