In the compound diet, the content of protein is too low, especially the animal protein is insufficient, which can not meet the needs of the body; The protein quality of feed is poor; The lack of methionine, lysine and tryptophan will lead to protein deficiency. When ducks suffer from chronic dyspepsia or other gastrointestinal diseases, malnutrition such as protein's disease will also occur due to the decrease of digestive absorption rate.

Lack of protein will lead to slow growth, gradual emaciation, weight loss, reduced egg production, decreased egg weight and egg quality. Lack of various amino acids can cause different symptoms. When lysine is deficient, growth and development stagnate, emaciation, poor bone calcification and subcutaneous fat decrease; When methionine is deficient, the growth and development are hindered, the muscles atrophy, the feathers are dim, and the liver and kidney function are incomplete, which makes the deficiency of choline or vitamin B 12 more serious; When arginine is deficient, the male duck's sperm is inhibited, its reproductive ability is lost, its growth and development are hindered, its weight is rapidly reduced, and its wings and feathers are curled. When tryptophan is deficient, the growth is blocked, which is also one of the reasons for the smooth tendon.