Chitosan was tested for use as an ingredient for domestic animal feeds. (1) No abnormal symptom was observed with hens and broilers by feeding <1.4 g of chitosan/kg of body weight per day for up to 239 days, and with rabbits by feeding < 0.8 g of chitosan/kg of body weight per day for up to 239 days. (2) Both chitin and chitosan were digested 35-83% by rabbits and 88-98% by hens and broilers. (3) An increase in the serum cholesterol, triacylglycerol, and free fatty acid values of these domestic animals fed cholesterol-additive diets was suppressed by feeding 1.2-1.4 g of chitosan/kg of body weight per day for hens and broilers and 0.7-0.8 g of chitosan/kg of body weight per day for rabbits, but not by feeding chitin. (4) Hen's appetite and egg-laying rate decreased by feeding an excessive amount of chitosan for a long term (3.6-4.2 g of chitosan/kg of body weight per day for 189 days) because of incomplete digestion of chitosan. © 1990, American Chemical Society. All rights reserved.