Oxidative status of dairy cows fed flax meal and infused with sunflower oil in the abomasum

Technical note: Quantification of lignans in the urine, milk, and plasma of flaxseed cake-fed dairy sheep

Mammalian lignans are phytoestrogens with important bioactivities, and their concentrations in livestock milk may influence the health of consumers. This research aimed to establish a method to quantify multiple mammalian lignans in the biofluids of dairy sheep using ultra-HPLC-triple quadropole mass spectrometry with multiple-reaction monitoring. Secoisolariciresinol, 2-[(4-hydroxy-3-methoxyphenyl)methyl]-3-[(3-hydroxyphenyl)methyl]-1,4-butanediol, enterodiol (ED), enterolactone (EL), ED-sulfate (ED-S), and EL-sulfate (EL-S) were purified from the urine of flaxseed cake-fed dairy sheep. The structures of these lignans were identified by a combination of mass and nuclear magnetic resonance spectra. These purified lignans were used as standards to optimize their quantification conditions in urine, milk, and plasma of dairy sheep. On this basis, the lignan metabolites in biofluids were quantified. To improve analysis sensitivity, plasma and milk were pretreated with acetonitrile containing 1% formic acid and passed through a HybridSPE-PL 55261-U column (Supelco, Bellefonte, PA). The limit of quantification of the lignans ranged from 1.43 to 18.3 ng/mL in plasma, and from 1.01 to 18.7 ng/mL in milk. The linearity of the calibration curves ranged from their limit of quantification to at least 217 ng/mL in plasma, and 217 ng/mL in milk. Regression coefficient of the calibration curves were above 0.99 for secoisolariciresinol, 2-[(4-hydroxy-3-methoxyphenyl)methyl]-3-[(3-hydroxyphenyl)methyl]-1,4-butanediol, ED, EL, ED-S, and EL-S, indicating satisfactory relationships between the peak areas and concentrations in the quantification range. The relative concentrations of ED-glucuronide and EL-glucuronide (EL-G) in different biofluids were compared based on their chromatogram peak areas. The sheep plasma contained all forms of mammalian lignans (i.e., ED, EL, ED-S, EL-S, ED-glucuronide, and EL-G.); the urine contained ED, EL, ED-S, and EL-S; and the milk contained ED, EL, ED-S, EL-S, and EL-G. Milk-to-plasma concentration ratios of the mammalian lignans indicated that the free forms were more permeable than the sulfated conjugates. Mammalian lignans found in sheep plasma and milk may provide health benefits to the sheep and sheep-product consumers. The analytical method established in this work could be used to quantify mammalian lignans in livestock products.

A Review of Lignan Metabolism, Milk Enterolactone Concentration, and Antioxidant Status of Dairy Cows Fed Flaxseed

Lignans are polyphenolic compounds with a wide spectrum of biological functions including antioxidant, anti-inflammatory, and anticarcinogenic activities, therefore, there is an increasing interest in promoting the inclusion of lignan-rich foods in humans' diets. Flaxseed is the richest source of the lignan secoisolariciresinol diglucoside-a compound found in the outer fibrous-containing layers of flax. The rumen appears to be the major site for the conversion of secoisolariciresinol diglucoside to the enterolignans enterodiol and enterolactone, but only enterolactone has been detected in milk of dairy cows fed flaxseed products (whole seeds, hulls, meal). However, there is limited information regarding the ruminal microbiota species involved in the metabolism of secoisolariciresinol diglucoside. Likewise, little is known about how dietary manipulation such as varying the nonstructural carbohydrate profile of rations affects milk enterolactone in dairy cows. Our review covers the gastrointestinal tract metabolism of lignans in humans and animals and presents an in-depth assessment of research that have investigated the impacts of flaxseed products on milk enterolactone concentration and animal health. It also addresses the pharmacokinetics of enterolactone consumed through milk, which may have implications to ruminants and humans' health.