Background: Silymarin, the predominant compound of milk thistle, is an extract took out from milk thistle (Silybum marianum) seeds, containing a mixture of flavonolignans with strong antioxidant capability. Methods: The experiment was conducted using 70 Lohmann LSL-Lite hens at 80 weeks of age with 7 treatments each with 10 replicates. Treatments included: (1) control diet without silymarin, (2) daily intake of 100 mg silymarin powder/kg body weight (BW) (PSM100), (3) daily intake of 200 mg silymarin powder/kg BW (PSM200), (4) daily intake of 100 mg nano-silymarin/kg BW (NSM100), (5) daily intake of 200 mg nanosilymarin/kg BW (NSM200), (6) daily intake of 100 mg lecithinized silymarin/kg BW (LSM100) and (7) daily intake of 200 mg lecithinized silymarin/kg BW (LSM200). The birds were housed individually, and diets were fed for 12 weeks. Results: Scanning electron microscopy showed that NSM was produced with the average particle size of 20.30 nm. Silymarin treatment improved serum antioxidant enzyme activity. All groups receiving silymarin showed a decrease in liver malondialdehyde content, expression of fatty acid synthase, tumour necrosis factor alpha, interleukin 6 (IL-6) genes in the liver, and hepatic steatosis than the control, except those fed the PSM100 diet. There were decreases in liver dry matter and fat contents, non-alcoholic fatty liver disease and hepatocyte ballooning, and an increase in glutathione peroxidase gene expression and a decrease in iNOS gene expression in birds fed the NSM100, NSM200, LSM100 and LSM200 diets compared to the control group. Moreover, all groups receiving silymarin showed a significant decrease in liver weight compare to the control group. Conclusions: Overall, the effects of silymarin when converted to NSM or LSM and offered at the level of 200 mg/kg BW were more pronounced on the hepatic variables and may be useful in the prevention of the liver disease in older laying hens.
