Bioaccumulation and toxicity studies of lead and mercury in laying hens: Effects on laying performance, blood metabolites, egg quality and organ parameters

This study investigated bioaccumulation and toxicity derived from heavy metals in laying hens. The 160 52- week old laying hens were divided into 5 treatments with 8 replicates of 4 birds per pen. The treatments consisted of the control diet (without heavy metals), control diet with half the available dosage (AD, 5 ppm lead and 0.2 ppm mercury), AD (10 ppm lead and 0.4 ppm mercury), 2-fold AD (20 ppm lead and 0.8 ppm mercury), and 3-fold AD (30 ppm lead and 1.2 ppm mercury), and were provided to the laying hens for 8 weeks. Food and water were provided on an ad libitum basis at all times. Body weight and food intake were recorded once every two weeks, and eggs were collected and recorded daily. Two birds from each pen were euthanized to collect blood and organ samples on week 4 and 8. The 3-fold AD diet reduced food intake compared to that of the control and AD diets (P＜0.05). Hens fed the half AD diet had darker yolk compared to those fed the control and AD diet on week 4 (P＜0.05). Hens fed the 2- and 3-fold AD diets had increased relative liver weight, blood glutamic pyruvic transaminase and glutamic oxaloacetic transaminase levels (P＜0.05), while F1 follicle weights decreased on week 4 and 8. No difference was found in egg production rate, egg quality, ovarian follicle, blood metabolites including protein, globulin, albumin, and urea nitrogen throughout the study (P＞0.05). Heavy metal concentrations in the liver, eggs, and feathers were not detected at both week 4 and 8. Our results indicate that in-feed heavy metals for layer diets up to 30 ppm of lead and 1.2 ppm of mercury brought on hepatic dysfunction increasing blood metabolites that are associated with liver inflammation.