Since the initial announcement about the intended combination on March 9, 2010, both companies have worked diligently to create the proposed animal health joint venture, including submitting requests for the required antitrust reviews. The companies are discontinuing their agreement primarily because of the increasing complexity of implementing the proposed transaction, both in terms of the nature and extent of the anticipated divestitures and the length of time necessary for the worldwide regulatory review process. Merck and sanofi-aventis mutually determined that ending their plan is in the best interests of both companies and their respective shareholders, as well as the employees of Merial and Intervet/Schering Plough.

As a result of termination, both Merial and Intervet/Schering-Plough will continue to operate independently. The termination of the agreement is without penalty to either party and each party is responsible for its own expenses. 

—From Merck press release