Metabolism of flaxseed lignans in the rumen and its impact on ruminal metabolism and flora

Abstract

Lignans belong to a group of phytoestrogens found in many edible plants. They can be converted to mammalian lignans, namely enterodiol (END) and enterolactone (ENL), in non-ruminant animals. Previous studies have shown that lignans may possess estrogen-like biological properties and can interact with various enzymes and proteins in rats and human. Similar reactions in ruminants have not yet been demonstrated. The metabolism of lignans in the rumen and its impact on ruminal metabolism was therefore investigated in 6 Huainan goats fitted with permanent rumen fistulae and temporary jugular catheter which were supplied with flaxseed lignan (secoisolariciresinol diglucoside, SDG) via rumen fistulae. Low concentrations of END (0.017; S.D. = 0.024 mg/mL) and ENL (0.007; S.D. = 0.013 mg/mL) were detected in ruminal fluid of the goats fed the basal diet but concentration of SDG or mammalian lignans in the serum were below the detection level. Following SDG administration at 1 mg/kg body weight for 14 d, the concentrations of the three lignans increased (P<0.01). Concomitantly, the pH (P<0.05) and ammonia–nitrogen concentration (P<0.01) of ruminal fluid were decreased, while the concentration of microbial crude protein (P<0.05) and total volatile fatty acids (P<0.01) increased. Based on denaturing gradient gel electrophoresis profiles, SDG supplementation showed an effect on the rumen microbial profile. The results demonstrated that ruminal microorganisms efficiently converted SDG to END and ENL, and that SDG supplementation may improve ruminal metabolism of carbohydrates and nitrogenous compounds and influence the bacterial composition in the rumen of goats.