By Tom Polansek

CHICAGO, Aug 5 (Reuters) - Zoetis Inc, the world's largest animal-health company, plans to seek U.S. approval before the end of this year to sell its vaccine against a virus that has killed about 13 percent of the U.S. hog herd.

If approved, the new drug would rival the only vaccine available so far.

Zoetis, which was spun off from drugmaker Pfizer Inc last year, expects to ask the U.S. Department of Agriculture for a "conditional license" to sell its vaccine against Porcine Epidemic Diarrhea virus, or PEDv, Chief Executive Officer Juan Ramon Alaix told analysts during a quarterly earnings call on Tuesday.

The license would allow the company to sell the vaccine directly to hog farmers while it conducts further tests.

"There will be some limitations in terms of promotional activities, but not limitations in terms of selling the product to the market," he said.

The fast-moving virus has killed an estimated 8 million piglets since it was first identified in the United States last year, pushing U.S. pork prices to record highs.

Zoetis declined to provide details on the number of pigs the vaccine has been tested on, or on the results.

The USDA in June granted conditional approval to privately held Harrisvaccines to sell farmers the first vaccine against PEDv. Still, veterinarians have warned that outbreaks will likely surge this fall and winter because the virus thrives in cold weather.

The USDA declined to comment on Zoetis' plans.

(Reporting by Tom Polansek; Editing by Dan Grebler)