Role of glucosinolates in the causation of liver haemorrhages in laying hens fed water-extracted or heat-treated rapeseed cakes.

Glucosinolates were removed from whole rapeseed by a hot-water extraction procedure or depleted by heat treatment. When laying hens were maintained for three months on diets containing about 300 g kg-1 of these rapeseed cakes, the incidence of liver haemorrhages detected at post mortem examination was similar to that in birds maintained on 300 g kg-1 commercial rapeseed meal and significantly greater than in control birds fed soya-based diets. The effectiveness of glucosinolate extraction or depletion was determined by chemical analysis and by histological examination of the thyroid glands. Histologically the haemorrhages were similar after feeding extracted and commercial rapeseed meals. Diets containing mixtures of nitriles and glucosinolates severely depressed food intake and egg production but did not cause a greater incidence of haemorrhages than the other rapeseed products tested. Mortality from causes other than liver haemorrhage was higher with the diets containing rapeseed and this suggests that rapeseed has a more generalised effect on the body's defence mechanisms. These observations suggest that other factors in rapeseed meal, alone or acting with glucosinolates, may be responsible for inducing liver haemorrhages in laying hens.