Pfizer Inc said on Wednesday it will spin off its majority stake in animal health business Zoetis Inc to shareholders by allowing them to swap Pfizer stock for Zoetis stock at a 7 percent discount.

Pfizer, the largest drugmaker, sold Zoetis shares in an initial public offering in February that raised $2.2 billion. Pfizer retained an 80 percent stake in Zoetis after the IPO and now plans to unwind that, starting with this offer.

The offer would allow shareholders to exchange $100 worth of Pfizer stock for $107.52 worth of Zoetis stock.

Pfizer said the offer is expected to add to its earnings starting in 2014.

Zoetis shares were priced at $26 in the IPO and closed their first day of trading at $31.01. On Tuesday they finished at $33.04.

Pfizer owns 400,985,000 shares of Zoetis Class B common stock that it will convert to Class A shares for the exchange.

Pfizer shares were trading at $29.45 in premarket activity, up from a Tuesday close at $28.78.

(Reporting by Caroline Humer; Editing by Gerald E. McCormick and John Wallace)