ABSTRACT Lead (Pb) is a heavy metal, which adversely affects thyroid gland function and structure. Due to its high molecular weight and abundant functional groups, humic acid substances (HAS) can form chelates with heavy metals. The experiment was conducted to evaluate the prophylactic effect of HAS on thyroid hormone levels and histopathological lesions of laying hens exposed to lead (Pb) poisoning. After a week of adaptation, 192 Lohmann White laying hens (25 weeks of age) were fed one of four diets: a basal diet (BD) or the BD with HAS (0.15%), with Pb (0.3 g/kg), or with both. Experimental groups were replicated in 12 cages, with four hens each. Pb poisoning did not alter triiodothyronine (FT3; 3.22 ± 0.20 ng/dL) or thyroxine (FT4; 0.71 ± 0.08 ng/dL) concentrations, but caused a 167% increase in thyroid stimulating hormone (TSH) concentration. HAS supplementation returned the high TSH levels of hens exposed to Pb poisoning to normal values. Degenerative changes in the epithelial cells of the thyroid gland of the hens exposed to Pb poisoning were evidenced. Connective tissue cells in the interfollicular area and total amount of colloids with partially atrophic follicles were observed. These histopathological findings were less severe when HAS was added to the diet. In conclusion, HAS alleviates the effects of Pb poisoning on thyroid gland function and structure, possibly preventing its internalization by the tissue by forming chelates and exerting anti-inflammatory effects.

ABSTRACT Ninety-six 28-week-old Lohmann White laying hens were utilized to test the antioxidant effects of flavonoids (hesperidin, naringin, and quercetin at 0.5 g/kg diet) during an 8-wk experimental period. At the end of the experiment blood samples were collected to determine total protein, cholesterol, and malondialdehyde (MDA) serum levels as well as activities of glutathione reductase (GR), glutathione peroxidase (GSH-Px), glutathione-S-transferase (GST), and superoxide dismutase (SOD) and level of glutathione (GSH) in erythrocyte lysates. Data were analyzed using one-way ANOVA. Naringin supplementation did not alter serum cholesterol concentration, whereas hesperidin and quercetin supplementations decreased serum cholesterol concentration. Naringin and quercetin supplementations did not affect serum protein concentration. All flavonoids decreased MDA concentration as well as increased GSH-Px, GR, GST, and SOD activities and GSH level, being quercetion superior to hesperidin and naringin. In conclusion, flavonoids, especially quercetin, exert antioxidant activity, which may help improve wellbeing when laying hens are exposed to stressors.