Effect Of Flavin Containing Monooxygenase (Fmo3) Genotype On Trimethylamine (Tma) Content In The Chicken Egg Yolk

Choline is a precursor of TMA which causes a smell reminiscent of rotting fish preferentially in brown shelled eggs of chickens. Previously it has been shown that a non-synonymous A/T polymorphism in exon 7 of the chicken Flavincontaining Monooxygenase gene (FMO3) leads to an amino acid substitution (T329S) within a highly conserved motif which is supposedly involved in substrate recognition. The present study aimed to determine the effect of genotype resulting from this A/T polymorphism on the TMA content in egg yolks after feeding a choline rich diet. To determine phenotypic differences, first a photometric method was established to analyse the TMA content in egg yolks. In the experiment, 21 Rhode Island Red hens which were specifically selected for laying smelling eggs ("Tainters") were crossed with four White Leghorn males assumed to be "Non-Tainters" to produce F-2 hens. These hens were genotyped and TMA content in eggs was determined. In the first and third feeding period the diet was supplemented with 6000 mg choline/kg. Hens with TMA-N content greater than 5.6 mu g/g egg yolk were assigned to "High Group". This group showed exclusively TT genotype. In contrast, hens with a TMA-N content below 2.1 mu g/g egg yolk were assigned to "Low Group" and had both AA and AT genotypes. Within the Low Group, eggs of AT hens showed significantly higher TMA-N levels in the egg yolks than AA hens did. Identical distribution was found in third feeding period. In contrast, no differences were observed between groups when feeding of the choline rich diet was discontinued in the second feeding period.