However, in nature the mother hen can lay a clutch of up to fifteen eggs across fifteen days and yet still hatch every egg within a forty-eight hour window at the completion of incubation, producing a brood of beautifully finished chickens. How is this possible?

Managing egg age for seasonal demands

Several years ago, I was the manager of a turkey hatchery for one of Australia’s leading poultry producers. The facility was this particular company’s only turkey hatchery. Therefore it hatched every generation from pedigrees right through to broilers. Turkey meat remains to this day very much a seasonal dish in Australia. At Christmas time everyone wants to enjoy turkey. It is traditionally the centrepiece of the Christmas table. For the remainder of the year it is the preserve of caterers and restaurants. This meant that the egg stock that was required to satisfy the Christmas settings was vastly disproportionate to that which was required for the rest of the year. Managing egg age became a constant headache.

One amusing anecdote in particular remains with me from that time. We were putting together a setting of eggs to replace a breeder farm. The farm manager sent in his order and asked for seven hundred males of a particular line all to be hatched on the one day. His final requirement – by the time the birds reached maturity – was for one hundred males, however he wanted to be able to run a rigorous selection program so that he would know that the birds he was finally left with would be elite. It sounded like a lovely idea. There was, however one very large barrier to its execution; the source of eggs for this particular line of bird was a pen of forty hens. The hens were no longer in their prime. On a good day they returned twenty eggs, on a poor day five. Standard hatchability on fresh eggs from this particular line was 50%. After seven days of egg storage the hatchability would decrease dramatically. Twenty day-old eggs invariably returned zero hatchability. And to complicate the problem even further – the customer of course only wanted males, so therefore only half of the poults we were going to hatch were capable of filling the order; culls notwithstanding.

I attempted to explain these details to the customer and told him that in all honesty he would be lucky if he got twenty males above his final requirement let alone six hundred. He was, as you can imagine, considerably unimpressed.

If only hatchability could have been prevented from diminishing and we could have saved eggs for up to twenty days. Although I was ignorant of the fact at the time – this scenario is not impossible.

Restoring the viability to that of fresh eggs

A number of years later my wife and I established a free range enterprise of our own. For the poultry component of the enterprise we selected breeds that have been in existence hundreds of years, were slow growing but lent themselves to foraging outdoors; hard feather Indian Game, soft feathered Faverolles and a hybrid of the two. Due to the slow growing nature of these breeds we were able to set eggs weekly and manage egg age by that means.

During this time we became involved in a program to help preserve the progenitor of all poultry breeds, the Junglefowl. Our intention when embarking upon this breed preservation exercise was to collect the fertile eggs and set them in our incubators on a weekly basis. And this we did indeed do with great success. Only not all of the Junglefowl hens were willing participants. Their instincts had hardly been diluted from those of their ancient ancestors – they wanted to hatch their own eggs and raise their chickens themselves. In this pursuit they proved to be incredibly crafty. We had individuals who went to the extreme lengths of escaping their enclosures so that they could lay their eggs in the kitchen garden or deep within the raspberry patch. Having laid each day’s egg they would then return to the enclosure and behave as though nothing was amiss to deceive us from discovering and interrupting their ultimate plan.

Having completed their clutch of eggs, they would then commence sitting, disappearing completely. Often we wrote these missing hens off as having been lost to predators. Sometimes we would catch glimpses of them in the early morning hours as they allowed themselves a few stealthy moments to eat, drink and answer the call of nature. Then, three weeks later they would re-appear triumphantly; batches of perfectly hatched progeny in toe. I was always envious of the quality of the chickens that these hens could produce and I was always amazed that a clutch could contain as many as twenty eggs – and certainly no less than twelve - each laid a day apart and yet all of the chickens were of comparable quality and invariably superior to what I could produce out of a commercial incubator.

So – how was this possible? Considerable research has been made into the science of very early embryo development. The cell development of fertile eggs has been studied under the microscope and cell multiplication has been categorised into recognisable stages, giving us a better understanding of what enables an egg to survive.

There are authors far more qualified than I to whom the task should fall to describe the particulars of this research. However, in layman’s terms it can be put simply that the viability and likely hatchability of an egg decreases as it gets older due to the progressive dying off of embryonic cells. In the commercial hatchery this takes place in the egg store where eggs are put into embryonic stasis in temperatures below 20°C. Research has gone on to show that under very controlled conditions, eggs that are going to be kept for extended periods of time prior to setting can have their likelihood of hatching increased by exposing them to temperatures that promote cell division.

Therefore the mother hen, as she returns to her nest each day to increase the size of her clutch, is intrinsically aware that by pre-incubating the eggs she has laid previously, she is restoring their viability to that of fresh eggs. By the time she has laid her final egg, every single egg in her clutch is equal in cellular development and therefore prepared to begin embryonic growth at exactly the same rate. It is via this means that she is able to hatch the first egg that she laid and the last egg that she laid within forty eight hours of each other.

If only I had been aware of this during my tenure at the turkey hatchery. If only I had been able to use a Re-Store machine. One never knows – but it is possible that the displeased customer may have received his seven hundred turkeys.

Steve Evans has worked for one of Australia’s largest intensive poultry farming integrations and now operates a free range farming enterprise of his own. He is also consultant for Petersime.

Steve Evans, Petersime consultant