Purified Zearalenone at the Regulatory Limit Exhibits No Overt Toxicity in Broilers

Zearalenone (ZEA) is a prevalent non-steroidal estrogenic mycotoxin in feed and feedstuffs. This study investigated the effects of graded dietary purified ZEA standard (0, 0.2, 0.5, 1, 2, and 4 mg/kg) on growth performance, blood biochemistry, oxidative stress, immune response, intestinal morphology, histopathology, and gut microbiota in broilers. The use of purified ZEA standard eliminates confounding effects from co-occurring contaminants and the reduced nutritional quality of naturally contaminated feed, allowing an accurate assessment of ZEA-specific effects. A total of 216 one-day-old Arbor Acres male broilers were randomly allocated into six treatment groups, each with six replicates of six birds, for a 42-day trial. At the regulatory limit (0.5 mg/kg) and below, no overt toxic effects were observed on growth performance, hematology, or serum biochemistry. Although alterations in oxidative stress markers, specifically decreased liver superoxide dismutase (SOD) activity and reduced ileal glutathione peroxidase (GSH-Px) activity, and in immune markers, including increased interleukin-2 (IL-2) levels in the jejunum and ileum and decreased ileal interleukin-10 (IL-10) levels, were observed at 0.2-0.5 mg/kg, these changes did not cause tissue damage or functional impairment. Toxicological alterations emerged only at higher doses (1-4 mg/kg), comprising impaired jejunal morphology and moderate lung secretory cell metaplasia. The highest dose (4 mg/kg) further induced severe renal tubular degeneration and necrosis, accompanied by significant disruption of the jejunal microbiota. In conclusion, these findings indicate that purified ZEA at the regulatory limit exhibits no overt toxicity in broilers, although higher contamination levels pose clear risks to intestinal, pulmonary, and renal health.