Dose Effect of Milk Thistle (Silybum marianum) Seed Cakes on the Digestibility of Nutrients, Flavonolignans and the Individual Components of the Silymarin Complex in Horses

SIMPLE SUMMARY: Silybum marianum is a well-known herb in terms of its pharmacological activities, and it is used as both a medicament and a dietary supplement (phytobiotics). Milk thistle seeds contain a mixture of flavonoids known as silymarin, which consists of silybin, isosilybin, silychristine, and silydianin. Until now, there has been no evidence of monitoring the digestibility of silymarin complex in horses. The aim of the research was to evaluate digestibility of silymarin complex and the effect of nutrient digestibility in horses. Different daily feed doses of milk thistle expeller (0 g, 100 g, 200 g, 400 g, 700 g) were administered to five mares kept under the same conditions and at the same feed rations. We monitored the digestibility of silymarin, digestible energy, crude protein, crude fat, crude fiber, nitrogen-free extract, crude ash, calcium, phosphorus, and plasma profile. Statistically significant differences (p ≤ 0.05) were found between daily doses in digestibilities of flavonolignans and nutrients. Our findings showed the digestibility of flavonolignans increased with the daily dose and then stagnated with the dose of milk thistle seed cakes at 700 g/day. ABSTRACT: Milk thistle seeds contain a mixture of flavonoids known as silymarin, which consists of silybin, isosilybin, silychristine, and silydianin. Until now, there has been no evidence of monitoring the digestibility of silymarin complex in horses. The aim of the research was to evaluate the digestibility of silymarin complex and the effect of nutrient digestibility in horses. Different daily feed doses (FD) of milk thistle expeller (0 g, 100 g, 200 g, 400 g, 700 g) were administered to five mares kept under the same conditions and at the same feed rations. Digestibility of silymarin complex was monitored by HPLC-UV. Digestible energy (DE), crude protein, crude fat, crude fiber, nitrogen-free extract (NFE), crude ash, calcium (Ca), and phosphorus (P) were determined according ISO/IEC 17025:2017. The biochemical profile of blood plasma (total protein, albumin, alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), bilirubin, total cholesterol, HDL cholesterol, LDL cholesterol, triacyl glyceride (TAG), non-esterified fatty acid (NEFA), creatine kinase (CK), creatinine, urea, glutathione peroxidase (GSH-Px), total antioxidant status (TAS), glucose, calcium, and inorganic phosphate) was investigated. Moreover, the flavonolignans of the silymarin complex in plasma were detected. Statistically significant differences (p ≤ 0.05) were found between daily doses of milk thistle expellers in digestibilities. Our findings showed the digestibility of flavonolignans increased with the daily dose and then stagnated with the dose of milk thistle seed cakes at 700 g/day.