State animal and human health experts in three states who work closely with veterinarians and farmers said the government tally is likely an undercount because farmers are fearful of the economic hardship brought by a positive test, including being restricted from selling their milk or cattle for weeks.

U.S. farmers’ testing refusal skews bird flu count

Dairy producers fear economic losses from positive tests, but health officials say testing is key to limiting human spread

The U.S. avian flu outbreak in dairy cattle is much larger than official figures suggest, due to farmers' reluctance to test their animals and risk the economic consequences of a positive result, according to interviews with dairy experts, veterinarians and farmers in six states with known cases.