EFFECTS OF RETINOIDS ON IMMUNE-RESPONSES IN BIRDS

Vitamin A is an essential nutrient that has an influence on immune res ponses in birds. Both low and high vitamin A intakes result in impaire d immune responses. Low dietary vitamin A has been shown to cause redu ced antibody production, defective T-cell responses and reduced phagoc ytosis, and decreased resistance to infection by bacterial and viral p athogens 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 vita min A intakes that were 3-10 fold higher than NRC recommended levels.