Effects of milk thistle meal on performance, ileal bacterial enumeration, jejunal morphology and blood lipid peroxidation in laying hens fed diets with different levels of metabolizable energy
Milk thistle (Silybum marianum) is an annual or biennial plant belonging to the family Asteraceae. Dried milk thistle seeds contain 150–200 g/kg oil (Lau, 1998), and its oil extraction residue contains various flavonoids such as silymarin (Kvasnicka, Bıba, Ševčı[Combining Acute Accent]k, Voldřich, & Kratka, 2003). Moreover, about 80% of the bioactive components of milk thistle have antioxidant effects (DiCenzo et al., 2003). This medicinal plant is an effectual remedy in treating liver diseases or such syndromes as fatty liver.
Gawel, Kotonski, Madej, and Mazurkiewicz (2003) indicated that dietary inclusion of silymarin increased hatchability and subsequently improved body weight gain in broilers and turkeys. Tedesco et al. (2004) observed an increment of 14.38% in broiler body weight gain in response to the dietary supplementation of 600 mg/kg silymarin. Ducklings reared under oxidative stress and receiving diets containing 200 mg/kg silymarin weighed heavier than those fed the control diet (Yi et al., 2012). Nevertheless, Schiavone et al. (2007) and Blevins et al. (2010) did not observe any beneficial effects of dietary administration of silymarin on the productive performance of broiler chicks while Schönfeld, Weisbrod, and Müller (1997) reported diminishing feed consumptions after inclusion of 40 and 80 mg/kg of silymarin in broiler diets or 400 mg/kg in laying hen diets.
Compared to vitamin E, silymarin has been shown to exhibit a higher antioxidant activity (Vogel et al., 1975). Experiments have shown that silymarin elevates the superoxide dismutase activity in red blood cells and lymphocytes whereby the antioxidant capacity is enhanced in human cells (Feher et al., 1987; Müzes et al., 1990).
However, one of the beneficial strategies aiming to improve laying hens’ performance comprises an enhanced dietary energy level, especially from fat or oil sources, it may be associated with undesirable effects such as enhancement in blood and egg cholesterol, hepatic enzyme activities and/or systemic or peripheral lipid peroxidation (Han, Sung, Yoon, Lee, & Kim, 1993). Nevertheless, the previous results demonstrated that nutritional adjustments by incorporating medicinal plants in the feed could potentially amend such alterations (Nassar et al., 2007; Yi et al., 2012).
The effect of milk thistle meal in poultry nutrition has rarely ever been studied, and the present knowledge of this valuable meal is scant. The present study was therefore designed and implemented to evaluate the effects of including different levels of dietary milk thistle meal on the productive performance, blood metabolites, ileal microbial counts, lipid peroxidation as well as intestinal histology in laying hens fed either with low‐ or high‐energy diets.