I had never thought much about what determines the size of a chicken egg until last week.

Kyalo, my new worker, greeted me that morning with a crate full of eggs the size of those of a quail bird. Okay, you had not heard much about Kyalo because he joined the enterprise a few months ago and he has been on probation, meaning if I had written about him, perhaps I would have talked more about his faults.

My customers have never complained about the size of the eggs I sell them at Sh20 each, but what I know is that small eggs fetch lower prices. Therefore, if you want to maximise returns, increase the size of your eggs.

Now, if you don’t know this, you are probably a table farmer.

When it comes to chicken eggs, size matters. In fact, there are six official sizes of eggs, and the smallest you are likely to find on supermarket shelves are the medium eggs. Egg sizes are strictly determined by weight, meaning, you must use a chicken scale, not by eye-balling.


A simple way to look at this is to move from the largest (jumbo egg) that weighs about 70g, to the smallest (a peewee) that will weigh 35g. In between, you have the extra-large, large, medium and small eggs weighing 64, 59, 50 and 43g respectively.

To determine where my eggs fall, I asked my niece, Tumaini, to weigh two crates of eggs, one by one, and work out the average weight.

I realised that my birds have been laying eggs that average 60g, with a range of between 56g and 70g. That means the eggs fall between medium and extra-large.

An easier way to get the average weight of an egg would have been to weigh a full crate, subtract the weight of the empty crate and divide the total by 30.

Christine Kilonzi (left) and fellow farmers

Christine Kilonzi (left) and fellow farmers with birds they keep. PHOTO | LEOPOLD OBI

But what determines the size of an egg? The experts I consulted mentioned the breed, age and diet. I couldn’t agree more based on my personal observations.

In a way, the breed determines the size of the hen and as a general rule, the larger the hen, the larger the eggs. Consequently, different breeds will lay eggs of different sizes.

For example, I cannot compare the size of the eggs produced by my kienyeji chicken in Busia raised under free-range indigenous conditions to those from Kari Improved Kienyeji I raise in Nairobi. The egg size of the former ranges between 30 and 40g.


The bigger the hen, the larger the eggs and the bigger the breed-type, the larger the eggs. Big breeds like the Leghorns tend to lay larger than average eggs.

I have also observed with my Kari Improved Kienyeji chicken that the egg size increases as the hen matures. For example, by the time my chickens were into their one-year laying cycle, some eggs were weighing as much as 89g.

In other words, as the hens reproductive system matures, so does the egg size. That means that by the time a hen is into the two to three-year cycle when egg production starts falling, egg size increases.

Now this is no brainer. If the size of a bird determines the size of the egg, it follows that a diet rich in proteins and fatty acids that allows a bird to maximise its growth potential will pay dividends later.

Therefore, beside the genetics, using poor quality chick and growers mash is detrimental.

An animal production expert I spoke to explained how protein level in the feed can be used to alter egg size at different stages of production.

“In the first months of egg production, feeding a high of 18 to 20 per cent protein layer ration will increase egg size. After the flock has reached maximum egg production, high protein diets no longer promote large increases in egg size.


After 36 weeks of age, feeding rations with 15 to 17 per cent protein will help to slow increases in egg size,” Dr Silas Obukosia informed me.

The agricultural biotechnologist further explained why farmers must pay attention not only to the quantity but the quality of feeds given to hens.

“Productivity in livestock depends on genetics, feed conversion efficiency, disease-control and feed quality. Poor quality feeds can lead to slow growth, low egg production, diseases or even death. When making poultry feeds, you have to select and mix the ingredients correctly for optimum performance. It helps to test the raw materials and finished product for quality.”

Feed intake has a direct impact on the hens’ intake of nutrients and, therefore, the size of eggs that they produce. On average, it takes about 2kg of feeds to produce a dozen eggs, so larger eggs are not without cost to the farmer.

Any factor that limits feed consumption, for example crowding, heat, stress or inadequate water supply, will reduce egg size.

The interesting thing is that the eggs that Kyalo brought my attention to weighed about 25g. They were too small for sale that I had to consumer them. I tasked him to identify that particular hen. He is still searching.