Zoo officials had previously said the USDA would investigate along with the Association of Zoos and Aquariums, an accrediting agency.
USDA spokesman Dave Sacks says investigators will be looking for violations of the Animal Welfare Act, which governs the treatment of animals in public exhibits.
Maddox Derkosh, of Whitehall, bled to death when he was attacked by the dogs after falling off a wooden rail on an observation platform overlooking the exhibit at the Pittsburgh Zoo & PPG Aquarium.
Sacks says there is no timeline for the investigation, though any violations found will be made public.
