"Some of these farmers are running their fans and cooling cells non-stop but are still losing a lot of birds," Stephen Stone, a University of Arkansas agricultural extension agent in Lincoln County told The Morning News.

Eddie Beard of Lincoln County said he lost 100 chickens from a house of 45-day-old birds on Wednesday, and 350-400 altogether from eight houses total.

"From about six or seven in the morning until about 10 or 11 at night, I've been running fans nonstop in the houses," Mr Beard said. "During the summer, we usually use two to two and a half times more electricity than normal."

Losing chickens to heat stress is not a new problem for poultry farmers. But Mr Stone said the recent practice of growing larger birds has compounded the problem. As a chicken grows larger, it is less able to handle high temperatures, he said.

Even a slight difference in the weight of a chicken can have a significant impact on its ability to endure heat.

Mr Stone said that one neighbouring farmers had reported collecting 200 dead birds from a house in one day and another, whose chickens were younger, collected only 40.

The heat is also making it hard for the chickens to put on the additional weight that the poultry companies want, Mr Stone explained, as the birds have less appetite on extremely hot days.

"Each farmer is on a different production schedule, so the farmers who are just getting chicks aren't having this problem," Mr Stone said.

He added that one farmer had experimented with a new way to cool the house by laying sprinkler hose on the roof and turning on the water.

"He said it helped but he still couldn't get the temperature where it needs to be," Mr Stone told the newspaper.