Immune response of chicks fed various levels of zinc

Five experiments were conducted to determine the effects of zinc intake on the immune response of chicks. Ancona chicks (Experiment 1), New Hampshire (Experiment 2), New Hampshire x Leghorn (Experiment 3), and broiler chicks (Experiments 4 and 5) were fed semipurified (Experiments 1, 2, 3, and 4) or corn and soybean meal diets (Experiment 5) containing from 8 to 88 micrograms zinc/g of diet. An extra group of chicks in Experiments 1, 2, and 4 were fed a diet adequate in zinc but at an intake similar to that of chicks fed the lowest zinc level in each respective experiment. Low zinc intake (less that 28 micrograms zinc/g of diet) suppressed body weight at all times measured. The effect of zinc intake on the size of lymphoid tissues was variable, but at 5 wk of age, chicks fed 8 micrograms zinc/g of diet had smaller bursae of Fabricius and thymi than those fed additional zinc. Zinc intake had no influence on the primary and secondary immune response to SRBC or delayed hypersensitivity to phytohemagglutinin-P (PHA) or human gamma globulin in Ancona and broiler chicks. However, zinc intake did have a small effect in chicks from the New Hampshire parents. In Experiments 1, 2, and 4 (at least at certain times), antibody titers were reduced in pair-fed chicks. Thus, although zinc supplementation at the levels of practical diets did not affect immune function, feed restriction did.