Are all eggs fertilised? 

A chicken embryo’s life starts inside the hen even before an egg is laid. Eggs of various sizes and maturity levels are present in the hen’s ovary.

By   |  Published: 14th Sep 2020  6:49 pm

Egg eaters have often panicked at the thought of cracking an egg open and finding a tiny chick inside. But is it possible? Almost all commercially sold eggs are not fertilized! This means that there is, in fact, no tiny chick embryo developing inside the egg. 

A chicken embryo’s life starts inside the hen even before an egg is laid. Eggs of various sizes and maturity levels are present in the hen’s ovary. Only the left ovary of hens is functional. An egg is released from the left ovary in hopes that a rooster’s sperm will fertilize it. This occurs around 24 hours before the hen lays the eggs. If sperm from the rooster is present, the sperm fuses with the hen’s yolk cell to form an embryo. The hard shell develops over the yolk before the egg is laid.

Hens do not know if the egg is fertilized and must go through with the egg-laying process either way. A hen will sit on the egg day and night in hopes of hatching it. Such hens are called broody hens and they are so dedicated that they only leave their eggs once per day!

Interestingly, hens are capable of laying eggs without a rooster’s involvement! An egg is produced by ‘laying hens’ in poultry farms once every 24 to 27 hours! All they require are the correct nutrients, namely calcium and vitamin D3 and the right physical conditions. Light stimulates the laying process, and some farms use artificial lighting to regulate the process during winter.

Even though there is no difference in the nutrient content or taste between a fertilized and an unfertilized egg, most commercial farms prefer to have only hens in their coops. This is because a single rooster can mate with 10 to 12 hens, and if proper care is not taken, the flock numbers can get out of hand very quickly!

In the wild, hens lay eggs until they form a clutch, a group of eggs that are hatched together. The clutch size differs from bird to bird. Hens usually have a clutch size of around a dozen eggs, after which the hen stops laying more eggs. Female fowl also stop releasing eggs in the harsh winter months, as it is difficult to raise offspring when food is in short supply. The shortened daylight hours also hamper egg production. This brings down the total egg production of wild hens, since they only lay in the spring. 

On the contrary, hens that are specially bred for egg-laying generate around 300 unfertilized eggs every year!

Over thousands of years, humans have selected those species of hens that produced more eggs. This is called selective breeding.  Laying hens have been modified over time to guarantee yield consistency and peak egg production by forcing hens to lay eggs daily and artificial lighting in the winter. The deliberate exclusion of roosters on poultry farms is the sole reason why these eggs are unfertilised.