Cyanogenic glucosides
Immature linseeds contain glucosidic substances such as linamarin, linustatin, and neolinustatin. At some temperatures (40-50°C), acidity level (pH 2-8), and in the presence of moisture, an enzyme (linase) releases hydrogen cynanide (HCN). In the normal oil extraction process, the high temperature destroys the linase and no HCN is released. However, unprocessed whole seeds and linseed meals processed under a low temperature can be toxic to animals (notably monogastrics), especially if the seed or the cake is wetted before being fed (McDonald et al., 2002). It is recommended to add seeds to boiling water (rather than cold water and bringing them to a boil) at least 5 minutes to rupture the seed coat. This allows the cyanide producing compounds to react and/or be destroyed by the heat, and evaporates any HCN produced. The cooked seeds form into a thick mucilaginous mass (Kohnke et al., 1999). Extraction with trichloroethylene or carbon tetrachloride destroys the glucosides (Przybylski, 2005).
Vitamin B6 antagonist
Linseeds contains linatine, a vitamin B6 (pyridoxine) antagonist, in concentrations ranging from 20 to 100 mg/kg. Symptoms of B6 deficiency can be observed in broilers fed linseeds, and it is recommended that diets containing them or linseed meal be supplemented with vitamin B6 (Newkirk, 2008).
Mucilage
Linseeds contain 2-7% of water-soluble carbohydrates, known as mucilage (mucins), which interfere with both processing and digestion (Przybylski, 2005). Mucilage absorbs water, increasing intestinal viscosity and causing a laxative effect. While this effect can be beneficial in humans, it can impair performance of livestock, notably in young birds (Alzueta et al., 2003). Adding fibre-degrading enzymes and gradually introducing linseeds have been suggested to alleviate these antinutritional effects (Slominski et al., 2006).