LITTLE ROCK, Ark. (AP) — Tyson Foods Inc. has begun killing and burying the carcasses of 15,000 hens from a flock that tested positive for exposure to a strain of the bird flu in northwest Arkansas, state officials said Tuesday.

Tyson said preliminary tests on the flock indicated the presence of antibodies for H7N3, a less virulent strain of the virus.

Routine blood tests conducted Friday found the possible exposure, said Jon Fitch, director of the state's Livestock and Poultry Commission. Further tests done by the state and the U.S. Department of Agriculture found the birds did not have active infections.