(Reuters) - The European Commission on Tuesday said it had opened an antitrust investigation into possible breaches of EU competition rules by U.S. pet products maker Zoetis.

The EU's executive said Zoetis was seen to have prevented the market launch of a novel biologic medicine used to treat chronic pain in dogs, which would have been a competitor for its 'Librela' medicine.

The EU said this meant Zoetis might have engaged in "exclusionary behaviour" by terminating the development of an alternative product that was going to be commercialised in Europe by a third party.

Librela is the first and only monoclonal antibody medicine approved in Europe to treat pain associated with osteoarthritis in dogs.

When developing Librela, Zoetis acquired another product for the same indication of pain relief, which was also in the later stages of development and would be commercialised by another company.

The commission said it was the first formal investigation into a potential abuse relating to the exclusionary termination of a pipeline product which was to be commercialised by a third party, and said it would carry it out as a matter of priority.