Pfizer's animal health unit on Monday filed plans with regulators for its initial public offering of stock.

The drug company had announced plans to spin off the unit through an IPO in June. The new company, which makes animal vaccines and medicine, will be called Zoetis.

Plans filed with the Securities and Exchange Commission call for Pfizer to sell as much as 20 percent of the new company to the public.  The filing did not give a price range for the shares that will be sold. The IPO is expected to take place next year.

The unit has about $4.2 billion in annual revenue, according to recent filings.

The animal health unit employs about 250 people in North Carolina, 160 of those in Durham at its global poultry headquarters. Many of those workers became Pfizer employees in 2007 when the drug giant bought Embrex, a Durham company that made poultry vaccines.