Although the cause, or causes, of the hemorrhagic syndrome is not pinpointed without question, there is a great deal of evidence that the major cause is mycotoxicosis. This condition has been caused when one or more species of molds has been isolated from the flock or feed of the birds. Among the mold species found and blamed are Alternaria, Penicillium and Aspergillum.

Field cases of hemorrhagic syndrome have been observed where birds have access to mold contained in one or more of the ingredients of feed. Often, mold will grow and be harmful where conditions for it are favorable, such as when feed is spilled around waterer. Combined with warmth in the brooder, spilled mash is an ideal growth medium for molds and formation of toxins.

Research workers have demonstrated without question that fungal isolates, when experimentally added to feed or litter, will proliferate and cause a toxic sis in chickens. When anti fungal compounds have been added to damp broiler mash containing harmful fungi, chickens consumed the feed without harm.

Birds that consumed the same mash without anti-fungal compound were affected by a severe hemorrhagic condition. Also, the research workers observed that if contaminated litter remained dry so that no fungal growth occurred, there was no hemorrhagic condition. When the same litter was dampened, however, allowing the fungi to grow and secrete their toxins, a hemorrhagic condition was observed.