Effect of lead and niacin on growth and serotonin metabolism in chicks.

Interactions of lead and niacin were studied in growing broiler chicks fed one of four experimental diets from day-old to 3 wk of age. The diets were a low niacin basal diet (LN), the basal diet supplemented with 40 mg of niacin/kg (control), the basal diet supplemented with 2000 mg lead/kg, as lead acetate (LN + Pb) and the basal diet supplemented with both niacin and lead (control + Pb). Growth and feed efficiency were reduced significantly by lead. The lead-associated growth depression was less severe in chicks fed the low niacin diet as indicated by a significant lead X niacin interaction. The relative weights of two brain regions (telencephalon and diencephalon) and the adrenal glands were greater in lead-treated chicks than in their nonlead-treated counterparts. Plasma and telencephalon tryptophan were lower in lead-treated chicks than in nonlead-treated chicks. Diencephalon tryptophan was lower in chicks fed the LN diet than in chicks fed the control diet. Brain serotonin was lower and 5-hydroxyindoleacetic acid was higher in both brain regions of lead-treated chicks than in nonlead-treated chicks. The data indicate that tryptophan and serotonin metabolism were altered by lead treatment, whereas niacin was without effect. The interaction of lead and niacin on growth does not appear to be related to alterations of serotonin metabolism in the central nervous system.