Pershing Square Holdings lost 7.3 percent in October, the firm, which invests roughly $16 billion for state pension funds, endowments and wealthy investors said on a Web site. The trouble was largely related to a 47 percent tumble in the stock of Valeant, a drug company Ackman added to his concentrated portfolio earlier this year.

But another one of Ackman's big bets on Platform Specialty Products also soured when it lost roughly 20 percent in the last month.

Last year Pershing Square Holdings gained 40 percent.

(Reporting by Svea Herbst-Bayliss)