EFFECT OF RAPESEED MEAL ON TRIMETHYLAMINE METABOLISM IN THE DOMESTIC-FOWL IN RELATION TO EGG TAINT

Shaver 585 hens were classified as tainters or non-tainters according to the trimethylamine (TMA) content of their eggs when they were fed a diet containing 10% rapeseed meal (from B. napus). They were then fed this diet or an equivalent soybean diet for 5-8 wk. Their ability to oxidize TMA was investigated by injecting 500 nmol of 14C-TMA/kg i.v. and by measuring the plasma levels of 14C-trimethylamine oxide (TMA.O). The tainters on the rapeseed diet gave a low flat curve (< 0.1 nmol 14C-trimethylamine oxide (TMA.O)/ml) while the non-tainters gave a much higher curve with a peak (0.47 nmol/ml) at 20 min. Higher peaks (0.6-0.7 nmol/ml) were given by the control groups. The tainters on the rapeseed diet also had lower plasma 14C-TMA levels for the first 45 min and excreted more radioactivity in the droppings, suggesting the involvement of another pathway of TMA metabolism. An experiment with Rhode Island Red .times. Light Sussex fowls confirmed the pronounced sensitivity of tainters to the depression of TMA oxidation by rapeseed meal and showed that their low plasma 14C-TMA.O levels were associated with low hepatic TMA oxidase activities (< 1 nmol TMA.O/mg protein per 30 min). Two of 10 adult cocks were similarly affected and therefore were analogous to tainters. The 14C-TMA test may be used for trials to breed out the tainting characteristic from commercial flocks.