A day in the life of an egg

The original purpose of an egg was a protective development chamber for an embryo to eventually produce a day old chick. Genetics and nutrition have led to current layer strains, aimed more specifically at producing eggs for human consumption.

The knack is to establish a successful partnership between you and your hens where these hens lay plenty of eggs capable of meeting stringent market requirements. Success is producing the highest percentage of saleable first quality eggs. The key to this success is understanding what can go wrong between egg formation and egg laying.

Previous articles in the Ranger have concentrated on what external factors, diseases, management, husbandry and nutritional influences may occur to foil this success. This article will concentrate more on what these stresses and strains mean to the egg on its passage from the ovary to the outside world.

This process can be likened to a car assembly line with different bits added at different stages as the egg travels along.

The ovary

The ovary has a rich blood supply and, hence, can act as a ’filter’. If there are bacteria in the bloodstream, they may settle in the ovary. Hence, bacteria, such as Salmonella enteritidis, can be incorporated in the organ at the outset and find their way into the egg. Salmonella vaccination tends to block this process.


The egg’s life starts in the ovary. The ovary looks like a bunch of grapes and is, in fact, a collection of yolk packages (follicles) of varying ages such that about one a day is ’ripe’ enough to detach itself. This procedure is under hormonal influence to control the rate of maturity of the follicles and the hormonal mechanism is influenced by the lighting programme. This explains why lighting programmes are so important in triggering the flock, as a whole, to ’come into lay’.

The colour of the yolk is determined by the diet of the bird and may be pale with severe worm infestations, due to poor absorption of pigments from the damaged intestines.

The oviduct

The second major organ is the oviduct. This is basically the production line, although it is a long flexible tube rather than a conveyor belt.

The infundibulum

The open end of the oviduct tube is a funnel-like structure, the infundibulum, which catches the maturing follicle as it drops off the ovary. Things can start to go wrong already. When a flock first comes into lay (and under certain dietary influences), more than one follicle can develop rapidly and drop into the infundibulum at the same time. These go on to be doubles.

The magnum

This is the longest and most obvious part of the oviduct. One major problem here is that as the oviduct is a long tube of circular muscle, it squeezes the egg along like toothpaste in a tube or like food moving along your intestines.


In the same way that you may suffer nervous diarrhoea under stressful circumstances due to unwelcome contractions of these muscles, any stress on your birds can upset the rate and direction of movement of the egg on its travels. The infundibulum may even contract and prevent the follicle gaining access to the magnum at all.

If this happens, the mature follicle has to go somewhere and drops off into the abdomen. Here it is likely to burst, irritate the delicate lining of the abdomen and lead to a sterile egg peritonitis. Hence it is not uncommon to see a blip in mortality at the onset of lay, especially if the flock is under stress.

The magnum is lined with glands and this is where the albumen (white) is coated onto the egg follicles. General stress and certain viruses can disturb these glands and result in very watery albumen being produced. This can lead to the all too well known problem of ’watery whites’ reducing those all important Haugh units and increasing seconds.

The magnum is a very vascular (blood rich) organ and again important but ill defined stresses can cause aberrant muscle activity leading to some small haemorrhages (bleeds) resulting in so-called ’blood spots’ in the albumen. If this is more severe, then small pieces of tissue may fall off the lining and can result in meat spots in the finished egg.

The Isthmus

The next section of the oviduct is the isthmus. This is a narrow section and here the egg membranes start to be laid down around the albumen to package it correctly. If these egg membranes are not laid down uniformly and accurately, the shell itself may be a disaster–they act like the foundations of a house!

The uterus (or shell gland)

The first section is a short tube called the tubular shell gland. Here calcium salts are deposited on the egg membranes to produce the first layer of bricks on top of the foundations. If this layer is built incorrectly, then the shell laid on top may be crooked, weakened, deformed, roughened or prone to cracks. The egg may only spend a short time here but it is critical to good shell development and hence the production of first quality eggs.

The second part is the true shell gland or pouch. The egg spends most of its time here (about 20 hours) and there is considerable increase in weight of the egg due to fluid and shell deposits. 95% of the egg shell is calcium carbonate, so good shell development is dependent on a good source of calcium for the bird, delivered via the feed, in a way the bird can effectively absorb it.

During this phase, lack of adequate perching space can lead to crowding of birds causing abnormal pressures on the bird’s abdomen and hence its unlaid egg. This can lead to misshapen eggs and cracks (especially equatorial) and other deformities.

The vagina

The egg has now virtually finished its journey and the vagina represents the ’waiting room’ prior to the selection by the bird of a suitable nest site for laying.

And this, like childbirth, may be the most dangerous part of the process. The hen is at her most vulnerable just after she has laid her egg and if not left to perform this task in peace and quiet, she may leave the nest prematurely and her red, glistening vent may be too much of an invitation to her sisters. Pecking can result leading to trauma and distress.

Furthermore, as the description of this journey has explained, the oviduct represents an opening from the vent right up into the abdomen of the bird. Any infection introduced here can find its way deep into the bird and lead to the condition we have all heard of and probably experienced in our flocks—egg peritonitis.

Incidentally, on the rare occasions that roundworms are found in intact eggs, they have travelled this same route up the oviduct into the albumen before the shell and its membranes are formed.

Conclusion

This torturous and arduous journey is as complicated as it sounds. A variety of disease, nutritional, management and physical stresses can have a potent effect on how well or how badly the egg develops. The initial development of an effective production line depends on producing consistent and mature point of lay pullets in the best possible condition and plane of nutrition. This is, again, an example of why efficient pullet rearing is so critical to good production.

The key then is to give the hen the best possible chance of smooth, stress–free egg production. We all want a quiet life, but contented hens lay good eggs.