Ackman's Pershing Square Capital Management is trimming 16.85 million shares from his position in Zoetis, with a price range of $46.75 to $47, the Times reported. The sale would bring Ackman's holding to 25 million shares, according to the report. Zoetis's stock is down almost 3 percent this year, closing at $46.56 a share Tuesday.
Ackman took a $1.5 billion stake in the former animal health arm of Pfizer in November 2014, the Times reported. Shares of the Zoetis are up nearly 16 percent since then.
William Doyle, a representative from Pershing Square who was elected to the Zoetis board of directors last year, will step down from his position this week, according to the Times.
It's been a tough year for Pershing Square. The fund is down more than 26 percent in 2016, largely due to its position in the embattled pharmaceutical giant Valeant. The company is under federal investigation because of drug pricing policies.