Controlling coccidiosis helps prevent histomoniasis in broiler pullets

The incidence of histomoniasis, commonly known as blackhead disease, is increasing in Southeastern US broiler-breeding operations — and young breeders 25 to 30 weeks old seem particularly susceptible, C. Stephen Roney, DVM, clinical associate professor at the University of Georgia’s Poultry Diagnostic and Research Center reported at the 2018 Western Poultry Disease Conference.

Based on data he’s collected, Roney said blackhead disease prevention requires producers to pay close attention to pullet-house floor management, coccidiosis vaccination and worm-control programs. Recent outbreaks have resulted in mortality rates as high as 6% and egg production suffers in birds that survive infections.

Post-outbreak treatment options are very limited. A combination of the Food and Drug Administration’s nitroimidazole antihistomonal ban in the 1990s, recent voluntary manufacturer withdrawals of phenylarsonic acids and parasitic worm drug resistance creates a “perfect storm of therapeutic inadequacy,” he said.

Histomoniasis infects breeding broiler pullets when egg production begins to peak. Postmortems of infected chickens reveal oocysts and cecal cores of Eimeria tenella, the parasite responsible for hemorrhagic coccidiosis.

Liver lesions typically found in turkeys with blackhead disease may or may not be present, Roney said.  He thinks E. tenella infection predisposes broilers breeders to Histomonas meleagridis, the parasite that causes blackhead disease.

Citing poor pullet immunity as a possible reason why infected birds succumb to the disease, Roney also faulted genetic programs aimed more at meat production than disease resistance.