Abstract

Since 2010, an enigmatic new form of acute mortal-ity in broilers has been observed in Belgium and the Netherlands. Field reports indicate that dying birds are hyperthermic with body temperatures of up to 46°C. In addition, the underlying litter temperature increases by 2 or more degrees Celsius. Affected birds are typically the heaviest males in fast-growing flocks. Mortality var-ies from 1 to 3 % during 1 to 3 consecutive days, mostly at 20 to 30 d of age, but may occur across the 14- to 42-d range. Occasionally, cortical blindness has been observed in birds from affected flocks. The only post-mortem findings are empty crops and intestines. En-larged livers and degenerated breast muscles are found in some cases. Compared with unaffected broilers, peri-odic acid-Schiff staining of the liver of affected broilers