The suspects are part of a gang with links to South American drug cartels, the Italian news agency ANSA reported.
The gangs used large dogs, such as Great Danes, Labradors and Mastiffs, as drug mules, ANSA said. The suspects made the dogs ingest 2.8 pounds of cocaine, and then later killed them to extract the drug.
ANSA said the gang is suspected of killing about 50 dogs.
The suspects could face charges of criminal association, drug trafficking and illegal weapon possession, ANSA said.