Cyanogenic glucosides
Immature linseeds contain glucosidic substances such as linamarin, linustatin, and neolinustatin. At temperatures between 40 and 50°C, with an acidity level between pH 2 and 8, and in the presence of moisture, the linase enzyme releases hydrogen cynanide (HCN). In the normal oil extraction process, the high temperature destroys the linase and no HCN is released, but unprocessed whole seeds and linseed meals processed under low temperatures can be toxic to animals, notably monogastrics, especially if the seed or the cake is wetted before being fed (McDonald et al., 2002). It has been recommended to add seeds to boiling water (rather than to cold water), and then boil for five minutes. This process ruptures the seed coat and allows the cyanide producing compounds to react and/or be destroyed, and any cyanide to evaporate. The cooked seeds form a thick mucilaginous mass (Kohnke et al., 1999). Extraction with trichloroethylene or carbon tetrachloride destroys the glucosides (Przybylski, 2005).
Vitamin B6 antagonist
Linseeds contain 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, mucilages or mucins, which interfere both with processing and digestion (Przybylski, 2005). Mucilages absorb water, increasing intestinal viscosity and causing a laxative effect. While this effect can be beneficial in humans, it can result in reduced performance in livestock, notably in young birds (Alzueta et al., 2003). Adding fibre-degrading enzymes and the gradual introduction of linseeds have been suggested to alleviate these antinutritional effects (Slominski et al., 2006).