Nothing could be simpler than an egg. Right? Wrong! The production of each and every chicken’s egg is Nature’s way of showing off her wonders. Eggs develop according to a strict sequence of biochemical and physical actions.
A female chick carries, from birth, thousands of yolks. At maturity each yolk is released into a tube called an oviduct and begins its journey to becoming an egg. The start of these eggs is triggered by light falling on photosensitive cells near the bird’s eye, firing a starting pistol on a journey of 25 hours from ovum to fully formed egg. This 25 hour transit time means that a laying hen will lay a fresh egg daily, one hour later each day – certain laying breeds such as leghorns are better at keeping up this kind of pace than others. For some, egg production in their prime would be 3 or 4 eggs a week.
During transit the yolk increases in size and is surrounded by albumen. It is then wrapped in a membrane and finally encased in the familiar shell. Shortly before the egg drops from the vent to the ground, pigment is deposited on the surface of the shell which determines the colour of the egg to be laid. A particular breed will lay a particular coloured egg, the most common being brown and white, for example Leghorns lay white eggs and Orpingtons lay brown – essentially the difference is only shell deep, despite the common misconception brown eggs are not any healthier than white.
At a certain point in the process the membrane around the egg is surrounded with a fluid comprising water, salt and calcium. From this mixture the shell forms in the shape of the uterus.
Hens have a single common orifice – called the cloaca – for the elimination of waste and for egg laying. Into the cloaca feed two channels. The oviduct and the large intestine. When an egg approaches the last section of the oviduct, the intestinal opening is blocked to allow transit of the egg. In this way the egg passes hygienically through the cloaca without coming into contact with waste matter.
Each chicken’s body contains ova at different stages of development. Some, the newest, will be tiny yolks. When mated with a rooster all the eggs in process at that point in time will be fertilized (assuming all other mating conditions are good). Those eggs which have progressed nearer the end of the oviduct will be larger and closer to being ready to lay.
Once the egg passes the cloaca, it is carefully expelled through a series of muscular contractions which convulse expelling the egg through the vent, an action often accompanied by a ‘cluck’.
Those involved with hens know well, that biologically, chickens have evolved to produce a clutch of eggs. Having a clutch can trigger a maternal instinct driving chickens to sit on their eggs but there are plenty of hens that will go broody in an empty nestbox as well so it is not always the case. However, from the point of view of minimizing the chance of her going broody and/or lessening the likelihood of an accidental (or intentional) breakage which could lead to a flock of egg eaters it is usually best to collect the eggs at least once a day. Presumably you would like the eggs anyway 🙂 If you want chicks to be hatched then exchanging false eggs for the real ones could allow your hen to build up a clutch which might encourage your hen to go broody (if that is what you want her to do) without you actually losing any eggs until it is certain that she wants to do the job. Broodiness can’t really be forced but it can be encouraged and that is one way to encourage it. Some hens are more prone to going broody than others (Silkies anyone?). Once a hen has gone broody she will stop laying until several weeks after the chicks have been raised.
Egg production uses up vital minerals which must be replaced. The process requires large amounts of calcium. As calcium drains away, comb, wattles and legs fade. To ensure health, calcium must be replaced. In commercial layers feed calcium (and the other nutrients needed) are already in the feed, but for older hens it may help them to have a calcium supplement available to them (they only take it if they feel they need it) such as oyster shell.
Millions of years of evolution have created the wondrous process by which eggs are created. It integrates biological, chemical and physical processes within a living creature in a unique way. Small wonder that there are so many people around the world, dedicated to the raising of hens for their eggs.