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 soya‐bean diet for 5 to 8 weeks. Their ability to oxidise TMA was investigated by injecting 500 nmol of 14 C‐TMA kg −1 intravenously and measuring the plasma levels of 14 C‐trimethylamine oxide (TMA.O). The ‘tainters’ on the rapeseed diet gave a low flat curve (<0.1 nmol 14 C‐trimethylamine oxide (TMA.O) ml −1 ) while the ‘nontainters’ gave a much higher curve with a peak (0.47 nmol ml −1 ) at 20 min. Higher peaks (0.6‐0.7 nmol ml −1 ) were given by the control groups. The ‘tainters’ on the rapeseed diet also had lower plasma 14 C‐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 x Light Sussex fowls confirmed the pronounced sensitivity of ‘tainters’ to the depression of TMA oxidation by rapeseed meal and showed that their low plasma 14 C‐TMA.O levels were associated with low hepatic TMA oxidase activities (< 1 nmol TMA.O nig −1 protein 30 min −1 ). Two out of ten adult cocks were similarly affected and therefore were analogous to ‘tainters’. It was concluded that the 14 C‐TMA test could be utilised for trials to breed out the tainting characteristic from commercial flocks.