It is a relatively inexpensive task to collect up fresh droppings and have a vet/vet school perform a fecal float to make a definitive Dx. If either the H.M. protozoan, or vector or other `flagellates' are ID'ed, then it would be best to treat all with Valbazen. Take chook droppings as well. They are the common asymptomatic reservoir (however, they can develop full blown symptoms): http://en.aviagen.com/assets/Tech_C...es/English/AviagenBrief_MaleHealth_June09.pdf Good reference: http://people.upei.ca/sgreenwood/SJG-VPM_122-Protozoa_Parasites-2012.pdf Yellow droppings? A brooding hen can eat a bad egg from her nest and then squirt a yolk colored modern art masterpiece in the run the following morning. Also seen in: Cholera/Typhoid/Erysipelas http://msucares.com/poultry/diseases/diseases.html Can HG/M actually cause the head to `turn black'? Usually, this occurs if the disease has resulted in significant deoxygenation of the blood (other reference mentions this results in secondary infections of end-stage disease preceding death). Conditions of every flock are different, and the health of individuals in each flock can result in a wide range of severity (with some diseases). Other cause of `Blackhead'? Sparring injuries: 
Since Pox was mentioned, I'll relate our recent experience. In late October our 7.5yr. old tom and his two 1yr. old male offspring were spending considerable time sparring (not unusual). A few days later we noticed that the tissue of the heads was swelling with no discoloration whatsoever. The first `scabbing' was observed around the base of the beaks. The swelling became so severe that the oldest tom was completely blind and the two younger ones were very nearly so. Early stage in the two younger toms (they quit fighting and pretty much cooperated in getting to the food and water): (click for larger images): 
Nearly two weeks later (one of the young toms): 
The oldest tom developed the wet form (yellow thin swellings in mouth/throat and, though tube fed for three days (couldn't get to food/hard time swallowing), he didn't make it. The younger toms fully recovered. The two hens never showed any sign, the two year old tom and 10 month old jake both had a couple of small scabs on caruncles and none of the chickens were affected. The sparring probably allowed the virus purchase.
Since Pox was mentioned, I'll relate our recent experience. In late October our 7.5yr. old tom and his two 1yr. old male offspring were spending considerable time sparring (not unusual). A few days later we noticed that the tissue of the heads was swelling with no discoloration whatsoever. The first `scabbing' was observed around the base of the beaks. The swelling became so severe that the oldest tom was completely blind and the two younger ones were very nearly so. Early stage in the two younger toms (they quit fighting and pretty much cooperated in getting to the food and water): (click for larger images): Nearly two weeks later (one of the young toms): The oldest tom developed the wet form (yellow thin swellings in mouth/throat and, though tube fed for three days (couldn't get to food/hard time swallowing), he didn't make it. The younger toms fully recovered. The two hens never showed any sign, the two year old tom and 10 month old jake both had a couple of small scabs on caruncles and none of the chickens were affected. The sparring probably allowed the virus purchase.
