Occurrence: Worldwide. Species affected: All. Age affected: All.

Causes: Deficiency of vitamin A in the diet. May occur when the vitamin is oxidised by rancid fat in the diet, and neomycin, a common antibiotic, decreases the absorption of vitamin A.

Effects: Caseous eye (no odour), emaciation, weakness, ruffled feathers, incoordination, eyelids stuck together (sicca), watery discharge from throat (roup), nostrils or eyes can be seen in young bird...