Eggs are high in nutrients and a versatile sweet or savoury ingredient.
However, does size matter?
The average size of eggs
The average hybrid hen will lay about 300 eggs from the time she starts to lay at 18-20 weeks of age to the end of her laying period around 72 weeks. At her peak she may lay one a day, but over time eggs are less regular.
These eggs will range in size from small to medium, large and a few extra-large. The age, breed and nutrition of the flock, their management and even the weather will affect the size of the eggs.
Egg size by hen age
Laying hens are professionally reared on a pullet rearing farm, where chicks are nurtured in customised conditions. At 16 weeks they are transferred to the laying farm where they settle in and develop further before they start to lay.
These weeks are crucial to the healthy development of the pullet – she needs to build body weight and strength and lay down resources to trigger the onset of laying eggs. With excellent care she will begin to produce eggs.
Small eggs (under 53g) initially for several weeks, and sometimes very small or oddly-shaped eggs.
Medium sized eggs (53g to 63g) follow as the hen develops, from around 22 to 37 weeks old.
Large eggs (63g to 73g) may be produced from 33 weeks of age onwards, but more commonly start from 40 weeks or later. This will depend on the breed and the feed being used.
Extra Large eggs (over 73g) are rarer, sometimes produced at the onset of lay when a bird produces two yolks at the same time, or towards the end of the laying period.
Producing an egg
Hen breeds in commercial egg farms come into lay at around 18-20 weeks of age, when their bodies have matured physically, and as lighting conditions trigger hormones to start the egg-laying cycle.
A laying hen’s ovary (she only has one) contains thousands of tiny ova, each capable of growing over the course of about a week into a nutrient-rich yolk. Then, in little more than a day, layers are added until the final, protective shell allows the egg to be laid.
Yolks provide most of what makes eggs a superfood, containing nutrients such as proteins, vitamins and minerals which would nourish a chick if the egg were fertilised (table eggs are not fertilised). Once the yolk is ready, it moves from the ovary into the oviduct, and over four hours layers of egg protein are added. This egg white, or albumen, is 90% water, but still contains useful resources of protein, vitamins and minerals, which are very nutritious. It is held in place by a fine membrane.
The egg shell forms in the shell gland over about 20 hours as layers of calcium carbonate are added. In the last two hours white or brown pigment is deposited on the outer layers of the shell, and a final bloom or cuticle provides protection against bacteria entering the porous surface of the shell. The egg is laid and the process starts again with the release of a fresh yolk into the system about 30 minutes later.
Image © 2021 Purina Animal Nutrition LLC.
Is egg quality related to egg size?
Egg quality is completely unrelated to egg size
A good quality egg depends on several factors:
The health of the laying hen
The hen’s welfare – principally whether she is stressed
The suitability of her feed and degree to which it is tailored to her needs
Egg size depends on:
The breed of laying hen
Her age and maturity
And, again, the suitability of her feed and degree to which it is tailored to her needs
You cannot identify a good quality egg simply by looking at its size.
A good quality egg of any size will have a smooth, strong shell that doesn’t crack easily. On cracking it open you will see a thick rather than watery white with depth and a raised surface, and a yellow yolk with no blemishes or smell.
The best way to ensure your eggs are high quality is therefore to buy from a supplier whom you trust to treat their hens properly and focus on their health and welfare.
A hen with adequate supplies of the right nutrition will have a body capable of producing a quality egg, with a nutrient-rich yolk and white, and a robust shell. Whether she can actually produce consistently good quality eggs will also depend on her physical condition and age – hens can easily be stressed by change as well as gut or other problems, and this will impact directly on the number or quality of eggs she lays.
As a hen’s reproductive system changes with age, the eggs she lays naturally become larger. Maximum egg size can be expected when birds are around one year old.
Too many large eggs can harm a hen
We have seen that naturally a laying hen will produce a range of egg sizes over her lifetime. However, if only the larger eggs sell, there is pressure on producers to disrupt this natural cycle and encourage their flocks to produce a larger egg than is usual for their age and breed.
As a hen’s reproductive system changes with age, the eggs she lays naturally become larger. Maximum egg size can be expected when birds are around one year old. However, physiological factors such as bird genetics, pullet quality, age and feed; and environmental factors such as lighting and temperature, can also play a role. By tweaking some of these factors a flock can be encouraged to produce a greater proportion of larger eggs within the constraints of the supplier’s breed targets.
It is not just the hen that can suffer as egg size increases – larger eggs tend to have thinner shells. There is a limit to the amount of calcium carbonate a hen can access from her diet and bones (around 4g) so there is a finite quantity of shell she can produce for each egg. If she lays larger eggs for any reason, the shell must stretch more thinly, making the egg less robust. This will increase the number of unsaleable eggs, or Seconds, causing waste as well as financial loss to the egg producer.
Egg-onomics
Ideally, egg producing farms would find a ready market for all good quality eggs produced by their flocks, irrespective of size. This is possible when selling eggs as mixed sizes into the independent marketplace, where consumers occasionally demand larger eggs for specific meals but generally accept natural variations in size (and therefore price). Schools, restaurants and those using eggs on a larger scale have always understood that provided the right total weight of eggs is used, how many or what size they are does not matter.
However, most producers have contracts with packers who market the eggs, largely for retail sale through supermarkets. Supermarkets dictate the size of the eggs they want on their shelves, and have recently demanded more large eggs, meaning consumers are led to buy these rather than considering what they actually need.
The fact that ‘large eggs’ are now stipulated in many recipes, rather than a total weight of eggs (a more accurate measure) may be behind this false demand for large eggs.
This supermarket drive for large eggs has left suppliers with too many smaller eggs.
Closure of many schools and restaurants due to COVID-19 has further reduced the market for these eggs, leaving producers with unsold eggs, or forced to reduce their price on small and medium eggs. Without action to correct the imbalance, millions of healthy hens laying high quality eggs are at risk, along with the livelihoods of egg producers, farm employees and all those along the egg-production chain whose goal is to provide pocket-sized nutrition to the nation.
So what can we do to help them?
First, help people understand that eggs naturally vary in size. They can be easily weighed if quantity is important, and the distinction between a medium egg of 62g and a large egg of 63g does not make it a better egg, just a bit bigger.
Second, guide people on which eggs to use. Just as potatoes are now sold as ‘for baking, roasting or salads’, savvy packers such as St Ewes are marketing larger eggs for breakfast boiling, medium ‘all-rounders’ for kids and baking, and ‘flavourful mixed size eggs’ as a natural selection box. With the right help it is likely that consumers would understand that they need not always buy large eggs – especially if this will help laying flocks lead healthier lives.
Eggs - a Sustainable Superfood
Across the world, families rely on eggs as a basic food source: rich in vital nutrients and ready for use in breakfast or baking, picnics or pasta. British poultry farmers follow high quality standards and companies like Wynnstay Humphrey Feeds & Pullets work hard to keep the flocks in their care healthy and productive.
