Two Blackhead Disease Outbreaks in Commercial Turkey Flocks Were Potentially Exacerbated by Poor Poult Quality and Coccidiosis.

Field visits at two different farms suggest a correlation between commercial turkey (Meleagridis gallopavo) flocks having increased mortality from blackhead disease (histomoniasis) if they suffer from poor poult quality at placement and coccidiosis (Eimeria spp.) before age 6 wk. In both cases, the flocks were all-in/all-out with curtain-sided houses and received a coccidiosis vaccine on day of hatch. At Farm I 2018, poults from different hatcheries were placed in two houses on the same farm (Houses 1 and 2). House 2 had poults considered poor quality and suffered from mortality associated with coccidiosis at 2 and 4 wk of age. At 8 wk, blackhead disease was diagnosed in both houses by postmortem examination. House 2 had mortality of >2000 poults, and the subpopulation of necropsied poults had gross lesions characteristic of histomoniasis. Gross lesions associated with blackhead disease were only found in eight poults in House 1, which was populated with good-quality poults and did not have a second spike in mortality due to coccidiosis. The Farm II 2020 poults were delivered from the same hatchery onto a three-house farm (Houses A, B, and C). House C had poults that were considered poor quality and had mortality associated with coccidiosis at 3 wk of age. At 8-9 wk, House C had mortality approaching 1000 birds, with all poults examined postmortem having clinical signs of blackhead disease. Houses A and B were populated with good-quality poults and had no diagnosed mortality from coccidiosis or blackhead disease. The similarity of these two cases suggest that poult quality at placement coupled with coccidiosis before 6 wk of age can influence the severity of blackhead disease in commercial turkey flocks.