Problems which limit the use of rapeseed meal as a protein source in poultry diets

The occurrence of a ‘fishy’ or ‘crabby’ taint in eggs and liver damage culminating in massive haemorrhage has greatly restricted the commercial utilisation of rapeseed meal as a relatively cheap protein supplement for laying hens in the UK. Recent work on these problems is reviewed. It has elucidated the cause of the taint and identified the rapeseed constituents that are involved. A genetic defect impedes the synthesis of trimethylamine oxidase in susceptible hens and goitrin and tannins inhibit the enzyme. This biochemical lesion severely impairs the metabolism of trimethylamine which is released from sinapine and other dietary sources of choline by enteric bacteria. Consequently, excessive amounts pass into the yolk and produce the taint. Liver haemorrhage is associated with hepatocyte degeneration, abnormalities in the biliary system and the leakage of cellular enzymes into the plasma. The toxic substance(s) responsible has (have) not yet been identified.