“…Valine, leucine, isoleucine, glycine, phenylalanine and tyrosine deficiency produce concave feathers, the feathers bending upwards from the body (Robel, 1977); lysine deficiency produces depigmentation (Fritz et al, 1946;Sanders et al, 1950) of turkey feathers and low arginine in the presence of normal lysine or methionine results in feathers with a retained sheath, loose barbules and thin rachis (Sanders et al, 1950). Lysine deficiency has been suggested as a cause of depigmentation of the feathers of psittacine birds (Harrison, 1984) but experimental work in cockatiels (Nymphicus hollandicus) has failed to confirm this (Roudybush and Grau, 1985).…”