My Pokémon Ranch was released in early 2008, and is compatible with Pokémon Diamond and Pearl. Following the release of Pokémon Platinum later that year, an update was released for Japanese players. The update, available for download in Japan since November 5, 2008, allowed the Platinum-exclusive formes for Giratina, Shaymin, and Rotom to be stored on My Pokémon Ranch, along with several other new features.
"I am wondering if there will be a Pokémon™ Platinum Version update for Pokémon™ Ranch?"
"I'm afraid there are currently no plans to make My Pokemon Ranch compatible with Pokémon Platinum Version, but we'll let you know if anything changes.