A flock from a turkey farm is presented with a mysterious illness. Several dead birds are notable, mostly younger animals.

Sick turkeys are listless, with drooping wings, unkempt feathers, yellow droppings. Sick older birds are emaciated.

Necropsy shows a yellowish green, caseous exudate in the ceca, cecal ulcerations and thickening of the cecal wall.

A typical liver looks like the image below.

What is the diagnosis?

Click here to see image

Click here to see image

Sorry.  You chose C, but the correct answer is B. Histomoniasis

This is histomoniasis; the combination of characteristic "bull's-eye" lesions on liver and cecal changes are pathognomonic.

Caused by protozoan Histomonas meleagridis, transmitted in eggs of cecal nematode Heterakis gallinarum.
Expect a depression/diarrhea presentation.

Expect to see more sudden death with necrotic enteritis caused by Clostridium perfringens.
Follow this link to see the so-called "Turkish towel" intestinal pseudomembrane of necrotic enteritis.

Signs of avian spirochetosis are highly variable, may be absent: see listlessness, shivering, increased thirst, green/yellow diarrhea with increased urates early on. Caused by a tick-borne Borrelia. Look for characteristic enlarged, mottled spleen with petechial hemorrhages, similar to Marble spleen disease of pheasants.

Expect depression, bloody droppings, substantial mortality with hemorrhagic enteritis of turkeys.
Follow this link to see hemorrhagic intestines. Follow this link to see characteristic enlarged spleen.

Expect diarrheal presentation with coronaviral enteritis of turkeys but NOT the characteristic cecal/liver lesions described on necropsy above.

For a good visual resource key poultry diseases, see the Cornell Atlas of Avian Diseases.

Ref: The USGS, Field Manual of Wildlife diseases, pp. 268-70.