Petco Holdings Inc is exploring the possibility of being acquired by PetSmart Inc, according to people familiar with the matter, in a merger that could create a company that accounts for more than half of the U.S. pet supply industry’s revenues. The preliminary talks between the two private equity-owned companies come after PetSmart ruled out a deal with Petco last year in favor of a sale to a buyout consortium led by BC Partners Ltd for $8.7 billion, including debt.