NEW YORK - Drugmakers Merck & Co and Schering-Plough Corp have received requests from U.S. antitrust regulators for more information on their proposed blockbuster merger.

Despite the second request from the Federal Trade Commission, the companies said on Monday they still expect the deal to close in the fourth quarter.

A Schering-Plough spokesman said the FTC request was primarily related to the companies' animal health businesses. Merck previously said it was exploring divesting its stake in its animal health venture with Sanofi-Aventis (SASY.PA) or selling a similar unit at Schering as part of the planned merger.

The companies said they had anticipated the FTC request and would cooperate fully.

Merck's acquisition of Schering, pegged at $41.1 billion when it was announced in March, would unite the makers of the cholesterol drugs Zetia and Vytorin.

Linda Bannister, a pharmaceutical analyst at Edward Jones, said she was not overly concerned about antitrust obstacles to the deal.

I think the issue is related to the animal health business specifically, Bannister said. I think there are plenty of other big pharma companies that are willing to take a look at those assets.

She added, I would be surprised if the merger doesn't close as planned.

Merck shares were down 49 cents, or 1.9 percent, to $25.42 in morning trading on the New York Stock Exchange. Schering was off 23 cents, or 1 percent, at $23.57, also on the NYSE. (Reporting by Lewis Krauskopf; Editing by Lisa Von Ahn and John Wallace)