Silymarin in the Diet of Dairy Cows and Its Impacts on Liver Health, Ruminal Fermentation, Productive Performance, and Milk Quality

The search for natural alternatives that improve the productive efficiency and metabolic state of dairy cows has driven the use of phytogenic compounds such as silymarin, a flavonolignan extracted from Silybum marianum L. Gaertn with recognized antioxidant, anti-inflammatory, and hepatoprotective properties. This study evaluated the effects of silymarin supplementation on the productive performance; milk composition; and ruminal, hematological, biochemical, and oxidative parameters of lactating Jersey cows kept in a confined system with robotic milking. Twelve cows (230 ± 30 days in lactation; 22 ± 3.5 kg/day of milk) were distributed in a crossover design, receiving a control diet (GCON) or a diet supplemented with 5 g/cow/day of silymarin (GSIL) for 28 days in each stage. Silymarin intake did not alter dry matter intake, feed efficiency, or average milk production (p > 0.05), but it increased milk fat content (4.27 × 4.02%; p = 0.05) and, consequently, milk production corrected for 4% fat (24.4 × 23.2 kg/day; p = 0.05). In the rumen environment, cows in the GSIL group showed higher concentrations of acetic acid (57.4 × 48.4 nmol/L), and total short-chain fatty acids (100.2 × 89.4 nmol/L; p = 0.01). Regarding the biochemical profile, silymarin reduced gamma-glutamyltransferase and aspartate aminotransferase activities, as well as haptoglobin levels, indicating a hepatoprotective effect, combined with a lower inflammatory response in the liver. Oxidative status was improved by decreased levels of TBARS (lipid peroxidation) and reactive oxygen species, as well as myeloperoxidase activity in the serum of cows fed silymarin (p ≤ 0.05), but there was no difference between groups for superoxide dismutase activity and glutathione levels. The inclusion of silymarin in the diet of lactating Jersey cows improved the antioxidant and hepatic profile, increased milk fat content, and favored ruminal fermentation, suggesting metabolic and productive benefits in confined systems with high physiological demands.