Rapeseed meal tannins and egg taint

The effect of fractions of a high-glucosinolate rapeseed meal (from B. napus) on trimethylamine (TMA) oxidation in laying hens was investigated in vivo and in vitro. When a tannin-rich fraction containing no glucosinolates was given for 14 days, the hens' ability to oxidise a standard dose of ¹⁴C-TMA was reduced by 32%. The TMA oxidase activity of hepatic microsomes was inhibited by 52–68% when they were incubated with three different tannin preparations. It was concluded that tannins play an important part in the inhibition of TMA oxidase and thence in the production of egg taint when rapeseed meal is consumed.