Effects of retinoids on immune responses in birds

Vitamin A is an essential nutrient that has an influence on immune responses in birds. Both low and high vitamin A intakes result in impaired immune responses. Low dietary vitamin A has been shown to cause reduced antibody production, defective T-cell responses and reduced phagocytosis, and decreased resistance to infection by bacterial and viral pathogens and protozoan enteropathogens. Enhanced immune responses can be elicited by high, but not excessive, dosages of vitamin A. Optimum immune responses in growing chicks and turkeys were obtained with vitamin A intakes that were 3-10 fold higher than NRC recommended levels.