Zoetis Inc. said Friday that it has adopted a one-year shareholder rights plan.

These plans, often known as “poison pills”, are intended to fight off hostile takeovers.

Zoetis said the plan would enable existing shareholders a right to buy preferred stock if a person or group acquires at least 15 percent of the company’s stock and tries to buy more.

This follows a report earlier this week that activist investor William Ackman had taken a stake in the animal health company and could push for its sale. Ackman’s firm Pershing Square Capital Management LP declined to comment on the matter.

Zoetis said at the time that it did receive a call from Ackman indicating that the firm has made an investment, but it declined to comment on details of that conversation. The Florham Park, New Jersey is holding an investor day next week, where it plans to discuss its business model and growth strategies.

Shares of Zoetis fell 10 cent to close at $43.14 Friday. Its share price is up roughly 36 percent over the past 12 months.

The company makes medicines for pets and farm animals. It was formerly owned by drugmaker Pfizer Inc., which spun it off last year.