Hepatic fatty acids profile, oxidative stability and egg quality traits ameliorated by supplementation of alternative lipid sources and milk thistle meal

Abstract

This study assessed the effects of different levels of milk thistle (Silybum marianum) meal (MTM) on egg quality traits, oxidative stability, blood biochemical parameters and liver health indices in laying hens receiving diets supplemented with lipid from different sources. For this purpose, Leghorn laying hens (Hy-Line W-36) were randomly assigned to 12 experimental treatments with eight replicates of five birds each. Dietary treatments consisted of four dietary fat sources (fish oil, sunflower oil, poultry oil and fat powder, each with different fatty acid profiles) and three levels of MTM (0.0, 15 and 30 g/kg) offered through 10 days of adaptation and 70 days of main recording. Results showed that dietary inclusion of polyunsaturated fatty acids, including fish or sunflower oils, reduced serum cholesterol content but increased blood malondialdehyde (MDA) concentration (p < 0.05). While fish oil improved the yolk colour index and Haugh unit (p < 0.05), it decreased yolk cholesterol concentration (p < 0.01). The highest hepatic glycogen content and tissue integrity as well as the lowest liver lipid percentage and MDA content were observed in birds fed diets supplemented with poultry oil. On the other hand, feeding 30 g/kg of MTM reduced not only hepatic lipid percentage but also aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities (p < 0.01), while it improved eggshell strength and thickness (p < 0.05). Supplementation of fat powder enhanced hepatic C16:0 content, while addition of poultry, sunflower or fish oil increased C18:1, C18:2 or C20:5 concentrations respectively (p < 0.01); nonetheless, feeding the highest level of MTM reduced hepatic ΣSFA but increased Σn-3 fatty acids (p < 0.01). The interaction effects indicated that fish or sunflower oil supplementation increased the MTM level required to reduce not only serum or egg cholesterol concentrations (p < 0.05) but also blood or hepatic MDA content (p < 0.01). It was concluded that fish oil and MTM (30 g/kg) supplements might improve internal egg quality traits and eggshell quality respectively. The hepatic fatty acid profile was also found strongly correlated with dietary fatty acids. Finally, the best hepatic health indices and the highest oxidative stability were achieved when the birds were fed diets supplemented with poultry oil and 30 g/kg of MTM.

Keywords: dietary fat sources; egg cholesterol; hepatic fatty acid profile; laying hens; milk thistle meal; oxidative stability.