Are yours the right size?

For many free range egg producers there is now absolutely no incentive to produce Very Large eggs. For many, the price received for Very Large eggs is now only one penny per dozen more than for Large ones. This is something of a problem for producers because it is difficult to know how to manage the flocks to produce neither Medium eggs (worth about 23 pence less than Large ones) nor the Very Large ones. In the ideal world how nice it would be if the weight of the majority of eggs fell within the 63 – 73g (Large egg) band. Geneticists – there is a challenge for you!!

Firstly, let us look at the straightforward correlation between the actual mean daily weight and the value of the eggs. This can be seen on Graph No. 1. It shows the rapid increase as the mean weight of the eggs progresses through the Medium and the Large grades and then the lack of a consistent increase when they reach the Very Large grade. In producing this graph, a well documented assumption had to be made that as the eggs get larger the shells get progressively thinner. With the value of Seconds being drastically lower than for Grade A eggs, there is clearly no benefit in producing Very Large eggs. The graph also shows that it is crucially important from the financial point of view to encourage the move from Small to Medium and then to Large eggs as quickly as possible. No surprises there!

In Graph 2, we look at the implications for the whole life of the flock. It is normal for the mean egg weight of free range flocks usually to fall in the 63.5 – 65.5 g band. Using the current egg prices, is there still an incentive to aim for a mean egg weight at the top of this range? The graph suggests that in theory but not in practice, a mean of about 65.5 g would probably be financially ideal. However, I think that 65.0 g is high enough as a mean to aim for. (We will look at this later in this article).

When reviewing the performance of a flock, it is usual to see quotes that show the percentage of Very Large and Large eggs. If that total is below about 60%, you could be doing better financially. However if it is approaching 70%, the hens may have been pushed too hard. It would be very surprising if the shell quality was optimal towards the end of lay if the total percentage of eggs in these two grades has reached about 70%.


It is essential that you liaise with the breeder representative and the nutritionists. Circumstances and breeds vary. However, usually the practical implications for management of free range flocks are:

a) When you receive the pullets, try not to trigger them into lay before the liveweight of most breeds has reached about 1.45 – 1.5 kg and the flock should have an even liveweight, with more than 80% of the pullets falling within 10% of the flock’s mean liveweight. Holding them back is feasible in the winter months. When the natural daylength is long however, it is crucial that the liveweights of the pullets are optimal, because in most free range houses the jump in day length triggers them into lay as soon as they are housed.

b) Encourage the new pullets to eat as much as possible. For most, but not all breeds, start them on a very high nutrient density feed. However do not use it for too long (say for more than up to 23 weeks). Change the feed then to a good quality feed that will sustain a good peak to production and at the same time allow the egg weight to increase rapidly into the over 60 g area.


c) Keep an eye on the daily Egg Mass Output (g) i.e. [% production x mean egg weight (g)] / 100. When this approaches 60g, it is advisable to change down a notch and ensure that the next delivery of feed contains a lower linoleic acid and methionine content. These are the factors that have the largest affect on the egg weight, so they should be reduced before escalating egg weight threatens to get out of control. The Metabolisable Energy should not be reduced at this time however.

d) A further change down of nutrients later in the laying period is often necessary, but not if the egg weight is well controlled. The timings of the feed changes are very important. If they are delayed, the egg weight may get too big (but not with all breeds).

Be proactive. If you wait until you are sure that a change is necessary, it could be too late. Usually you have feed in the bin and a delay between ordering the feed and its delivery. Therefore it could be up to say 10 days before the hens are actually eating the feed that should help in controlling their egg weight increase.

e) The geneticists of the majority of breeds claim that there have been changes that should reduce the risks of a run-away egg weight. Their aim is that there should be only a minimal increase after an egg weight of about 67 or 68 g is reached. To use their phrase "the egg weight increase reaches a plateau".

i) The blue line in Graph No. 3 is of a breed that makes this claim. This flock had an egg size that was allowed to escalate however, even though the egg mass output had got too high. An escalating mortality and increased Total Seconds are the penalties for this delay. It shows that there can still be an interaction between how the producer manages the flock and the breed’s genetic potential. In this particular case the management overrode the geneticist’s good intentions.

ii) The flock with the red line however has a genetic inability to produce eggs that are of an optimal size for the current egg price structure. It shows that there are some breeds where it is not possible to get a sufficiently large egg weight, even though this particular flock received a feed with a high nutrient density throughout its whole life. Clearly the potential for avoiding an uncontrollable escalation in egg weight is unlikely with this breed but the profitability of the flock is markedly reduced by its inability to lay eggs that are large enough for the current market requirements and price structure.

iii) The green line is for a breed that was almost able to cope with what is an optimal egg weight for the current egg prices. It is an interesting graph because even though there was a marked dip in egg weight just after peak production that was caused by an IB challenge, the egg weight rose to a size that resulted in the mean egg weight for the whole laying period to 72 weeks being 65.4 g. If one examines Graph No. 3, the green line provides a guide to what is the actual theoretical optimum weekly egg weight at the moment from the financial point of view. However it is a bit too adventurous. Total Seconds rose to about 16% towards the end of the laying period and the mean for the whole laying period was 9.7% i.e. too high. Therefore if your eggs are a bit lighter than the green line, you have probably reached a good and safe compromise.

When you take into account the risk factors of stress and a poorer shell quality, there is not a lot wrong with a mean egg weight of 65.0 g as a maximum to aim for. So don’t push your luck and aim for an egg weight that is too large and therefore stressful for the hens. However, ensure that your management is suited to the breed that you have chosen. Having chosen the breed with the optimal genetic potential, lighting patterns and nutrition are the tools that you should use to ensure that the eggs are neither smaller nor larger than they should ideally be. Small can be beautiful (but not financially). Larger is better but don’t let them get too big! So, are yours the right size?