If the eggs smell like that, throw them out – here’s why. “Caution”

It is not at all uncommon that in well-maintained rural and family farms and for no apparent reason, hens lay eggs which then smell like fish. This serious defect also appeared in industrial farms in the last century when its origin was discovered, which however was not, as some thought, the presence of fishmeal in chicken feed. The discovery of the origin of this serious defect which makes the eggs which stink of fish are no longer edible was only made with the knowledge of two different components: the nutrition and the genetics of the hens as well as the concomitant study people who stink of fish.

We’ve always known that some people stink of fish. The first scientifically studied clinical case in humans was published in 1970 in the medical journal “The Lancet”, when fish odor syndrome was identified as a rare metabolic disease called trimethylaminuria. This disease is caused by a genetic abnormality for which our body does not have the ability to degrade the trimethylamine present and therefore it accumulates and is released through sweat, urine and breath that emanate, therefore, a strong fishy smell from the body.

In humans, excessive production of trimethylamine can also result from an alteration of the microbiota, an altered metabolism or hormonal imbalances. The fishy smell of eggs is however a major problem, as even slight odors are noticed by consumers and lead to complaints. The odor contamination of the egg is due to the transfer and excretion of odorous substances, which result from an increase in ingestion or endogenous metabolism, in the egg, mainly in the egg yolk of trimethylamine . This happens for two conditions: the genetics of the hen and its diet. Already at the beginning of the 2000s, it was noted that certain types of eggs, in particular with brown shells, frequently developed the organoleptic defect of the smell of fish.

If the animals are fed with food very rich in choline, carnitine and lecithin whose metabolism comes from trimethylamine. Choline, carnitine and lecithin are mainly present in meat meals, therefore a non-normal food for hens, which eat vegetables instead; it was recently seen that the genetic defect of the hen concerns the polymorphic gene called FMO3 at the point of substitution of the amino acids. With a well-targeted selection, laying hens today do not have this genetic defect and even with a diet rich in choline, carnitine and lecithin they are able to produce eggs that do not smell like fish.