β-glucuronidase activity and enterolactone concentration in ruminal fluid, plasma, urine, and milk of Holstein cows fed increased levels of flax (Linum usitatissimum) meal

The main mammalian lignan present in milk of dairy cows fed flax products is enterolactone (EL), but the relationship between EL concentration in milk and body fluids when cows are fed increased proportions of flax meal (FM) is unknown. The objectives were to investigate the effects of increased levels of FM on EL concentration in milk, plasma, urine, and ruminal fluid and the activity of β-glucuronidase in ruminal fluid and feces. Eight rumen-cannulated cows were assigned to a double 4 × 4 Latin square design with four 21 d periods and four diets: control diet with no FM (CON) or a diet with 50, 100 and 150 g/kg of FM. Concentrations of EL in urine, ruminal fluid, milk, and plasma increased linearly with FM supplementation. Spearman's correlation coefficients were significant for all comparisons except that only a trend was observed between concentration of EL in urine and that in ruminal fluid before feeding. The strongest correlation was observed between EL concentration in ruminal fluid post-feeding and that in milk. Feeding increased proportions of FM in the diet had no effect on β-glucuronidase activity. Unlike to what is observed in non-ruminant animals, present results suggest that the activity of β-glucuronidase in the rumen is of little importance for the absorption of EL and its transfer in milk and other physiological fluids. Further studies are required to better understand and improve EL production and absorption, which could contribute to enhance animal health and the transfer of antioxidant components in milk.