Keith Poulsen’s jaw dropped when farmers showed him images on their cellphones at the World Dairy Expo in Wisconsin in October. A livestock veterinarian at the University of Wisconsin, Poulsen had seen sick cows before, with their noses dripping and udders slack.

But the scale of the farmers’ efforts to treat the sick cows stunned him. They showed videos of systems they built to hydrate hundreds of cattle at once. In 14-hour shifts, dairy workers pumped gallons of electrolyte-rich fluids into ailing cows through metal tubes inserted into the esophagus.

“It was like watching a field hospital on an active battlefront treating hundreds of wounded soldiers,” he said.

Nearly a year into the first outbreak of the bird flu among cattle, the virus shows no sign of slowing. The U.S. government failed to eliminate the virus on dairy farms when it was confined to a handful of states, by quickly identifying infected cows and taking measures to keep their infections from spreading. Now at least 875 herds across 16 states have tested positive.