How many dogs portraited lassie in the tv series?

In the original "Lassie" TV series, which aired from 1954 to 1973, the character Lassie was primarily portrayed by a Rough Collie named Pal. Pal was the original Lassie and appeared in the first few seasons, with his descendants continuing the role throughout the series. Over the years, several of Pal's offspring took on the role, but they were all part of the same lineage.