A branch of the H5N1 bird flu family tree that hadn't previously been seen in cattle has now been detected in dairy cows.

Nearly 119,000 birds have been culled at a farm in California after a bird flu called H5N9 was detected among the poultry

The detection indicates that distinct forms of the virus known as Type A H5N1 have spilled over from wild birds into cattle at least twice. Experts said it raises new questions about wider spread and the difficulty of controlling infections in animals and the people who work closely with them.

What you need to know about bird flu. Public health experts are closely watching avian influenza, which has affected chickens and cows and sickened some Americans.