Shares of Ackman's publicly traded vehicle Pershing Square Holdings, which trades in Amsterdam, dropped by around 10% on Tuesday to just over $13. The steep fall has to do with Valeant Pharmaceuticals, which was Pershing second largest equity position. Shares of Valeant plunged more than 45%, or $32 a share, to around $37 on Tuesday, after the company cut its earnings guidance and spooked the market.