Dietary flax meal and abomasal infusion of flax oil on microbial β-glucuronidase activity and concentration of enterolactone in ruminal fluid, plasma, urine and milk of dairy cows

• The gastrointestinal microbiota metabolize plant lignans into mammalian lignans.
• Microbial β-glucuronidase increases absorption of mammalian lignans.
• Abomasal infusion of flax oil has no effect on β-glucuronidase activity.
• Dietary flax meal has no effect on β-glucronidase activity.
• Dietary flax meal increases mammalian lignans in milk.

This study was performed to evaluate the effects of dietary flax meal (FM) and abomasal infusion of flax oil (FO) and their interaction on activity of β-glucuronidase in ruminal fluid and feces, and concentration of the mammalian lignan enterolactone (EL) in ruminal fluid, plasma, urine, and milk. Rumen fermentation characteristics and the pH in ruminal fluid and feces were also investigated to determine any potential interference with β-glucuronidase activity and EL concentration. Eight rumen fistulated lactating Holstein cows were assigned to a double 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments: (1) control diet with no FM (CON); (2) diet containing 124 g/kg FM (FMD) in the dry matter (DM); (3) CON and 250 g FO/day infused in the abomasum; and (4) FMD and 250 g FO/day infused in the abomasum. Abomasal infusion of FO had no effect on β-glucuronidase activity in the gastrointestinal tract and EL concentration of ruminal fluid, plasma, urine, and milk. Dietary FM and abomasal infusion of FO had no effect on fecal pH and microbial activity of β-glucuronidase in ruminal fluid and feces. Dietary FM increased concentrations of EL in ruminal fluid, plasma, urine, and milk. Molar proportion of propionate was increased and that of isovalerate was decreased with FM supplementation. Abomasal infusion of FO had no effect on ruminal concentration of ammonia N. Dietary FM had no effect on ruminal pH. As abomasal infusion of FO had no effect on β-glucuronidase activity in the gastro-intestinal tract and EL concentration, our results suggest that polyunsaturated fatty acids such as n-3 do not interfere with the absorption of mammalian lignans. Moreover, feeding 124 g/kg DM FM with a source of FA rich in n-3 bypassing the rumen increases EL concentration in physiological fluids of dairy cows, especially milk, which can be used as a strategy to optimize the concentration of mammalian lignans in milk and their potential beneficial effects on human health.