The practice, or “art”, of artificially incubating the avian egg dates back 3,000 years to the ancient Egyptian mud/brick oven-type rooms designed to incubate eggs from native fowl. Since the earliest practices of artificial incubation, the general goal of those incubators, as well as the incubators of today, is to mimic “nature’s incubator” or the mother hen.

In chickens, the feral hen incubates her clutch of eggs for 21 days, or about 504 hours, which has consistently remained the goal in artificial incubation systems, to mimic the mother hen. Therefore, the goal of artificial incubation is to pattern our practices after the mother hen and do what she does to achieve so much success. However, even with all the extensive research and modern technology available to us, modern equipment developed to implement this commercially sized artificial incubation, we still have much to learn to provide the embryo with the optimum environment to develop properly and uniformly.

In addition to the hen’s innate instinct and desire to incubate and hatch her eggs, she must respond to ambient environmental changes for the benefit of the embryo. The hen provides warmth to the eggs, mostly through direct contact of her skin to the egg with little, if any, forced air movement around the incubating eggs. This could explain why data suggests the mother hen provides warmer temperatures than most artificial incubators, and thus may not be as helpful for mimicking the hen’s daily incubation profile. Nevertheless, attempts to copy the natural incubation process remains the primary objective for commercial hatcheries and incubation design and operations.

Artificial Incubation

While modern incubation equipment can control conditions within the machines better than ever, the same basic principles of incubation still apply. Namely, we must control temperature, humidity, ventilation (air or gas exchange), and turning of the eggs. How well these conditions are met may vary with equipment age and type as well as their upkeep and maintenance. It is imperative to keep incubation equipment and the ambient environment working in the manner in which they were designed. Once these conditions are met, the incubation process is often thought to be a separate event from the grow-out phase of broiler production.

Embryo growth and the basic physiological development of the embryo should be considered to be the first three weeks of the broiler grow-out phase. In other words, the first three weeks of the broiler grow-out should be considered as occurring in the egg and in the hatchery as we know the effects of incubation conditions will affect the production level of the hatched birds as the the physiological makeup of the chick will have a lasting effect on the performance of the birds as they age. While incubation conditions can affect the physiological development and livability of the embryo, this will also affect the performance of the chick long after hatch. Taking this into consideration, there is much to be learned about the long-term effects of the environment we subject developing embryos to, in addition to hatchability and 7-day livability. As producers, we should be just as concerned about chick quality as we are about hatchability and chick numbers.

Room for Change?

One area receiving considerable attention recently is the effects of carbon dioxide (CO2) on embryo growth and physiological development during the incubation process. The long-held belief around ventilation or air/gas exchange during incubation was that a setter should work to continually remove carbon dioxide from the machine and replace it with oxygen. It has always been assumed that CO2 was harmful to the developing embryo and that fresh air and plenty of oxygen were needed for optimal chick development and hatchability. However, with atmospheric CO₂ levels typically hovering around 400ppm, and with the average measured CO₂ under the hen at around 4,000ppm it is obvious that the hen incubates her eggs to maintain a level of CO₂ above what is found in the ambient environment.
While the concentration level of CO₂ under the hen is dependent upon the age of the embryo and the frequency of which she remains on the nest, or leaves the nest (attentiveness), it is thought that she incubates her eggs at CO₂ levels substantially higher than atmospheric levels. Measurements as high as 10,000ppm of CO₂ have been measured under setting hens, so this is the peak level we should allow in the incubator.

Single-stage incubation systems that operate in a closed cabinet space can best control the environment in the cabinet. Most incubator manufacturers accept the need to control and monitor CO₂levels to produce the best chicks possible, and not just to replace it with oxygen, but to maintain specific levels of CO₂ for periods of time early in the incubation process. During embryo growth, the embryo utilises a lot of oxygen (O2) and produces excess amounts of heat and CO₂. As the embryo grows, its level of CO₂ production continues to increase at about 1,000ppm per day and continues for up to eight to ten days of incubation.

Therefore, at around eight to ten days of incubation, CO₂ is continually monitored closely to control peak levels (<10,000ppm) attained inside the incubator with the understanding that elevated CO2 levels late in incubation is detrimental to embryo livability. At the cellular level of the developing embryo, O2 and CO₂ exchange is occurring rapidly so, as the embryo grows in size and structure, the O2 demands and CO₂ production are increased. Therefore, the measure of gas exchange of eggs in incubation is simply a magnification of what is happening at the cellular level of the developing embryo.

While the overall goal of incubation is still to provide optimum conditions for embryo growth, technology has allowed for better control of these conditions, allowing for ‘fine tuning’ of the environment we create for developing embryos. Additionally, improved single-stage incubation equipment, allows our management programs to more precisely incubate eggs and provide the developing embryos with the exact environmental conditions necessary for the optimum growth of specific embryos rather than the average. As a biological entity, the chicken embryo is designed to grow and develop to survive. By controlling the ambient environment of the incubator cabinet, we can more precisely control the O2 and CO₂ in which we incubate chicken eggs.

Altering various incubator conditions, such as O2 and CO₂ levels during the incubation period, causes physiological changes in the developing embryo as it strives to survive. The physiological changes in the developing embryo will persist after hatching, and this has been well documented.
Therefore, the embryo develops in a slightly hypoxic environment that is suitable for growth, but it also causes the basal physiological development to be altered to survive. Data generated in conjunction with customers has shown that by controlling the CO₂ levels in Single-Stage cabinets the developing chicks thrive. A study with 1.6 million eggs set over several weeks, all from the same source flocks and divided between Single-Stage and Multi-Stage incubation equipment (Fig. 1) shows that we can gain better than 2.5% in hatchability.

Additionally, Fig. 2 also shows an increase in chick weight of 1.2 grams per chick.

A good measure of chick quality is their livability after placement in the growout barns. Fig. 3 shows data from the same set of eggs as previously mentioned and shows a 1.5% improvement in livability when eggs were incubated and chicks developed in Single-stage incubators where CO₂ levels were allowed to rise up to, but not more than, 10,000ppm.

Much like athletes who train at high altitudes to alter their physiology so that they can better utilise O2, young fowl hatched produce broiler chicks that are better prepared for the sometimes stressful conditions in which they are reared. The process of incubation is not entirely difficult; however, it requires paying attention to details in the hatchery as well as following the needs of the embryo and following the pattern of incubation that ‘nature’s incubators’ (the mother hen) has set for us.
The domestic fowl begins sitting on her clutch of eggs after she has laid her last egg so that all eggs develop on the same timeline and subsequently hatch after 21 days. Her process of incubation creates a very uniform environment that results in chicks hatching in a 24-hour hatch window (first to last chicks hatched), so they can all begin life as one collective unit. Any delays or aberrations from following what nature has taught us about incubation would go against what is biologically normal for the incubation and hatching of chicks, and could be considered a breach of animal welfare as it is not ‘normal’. Let’s begin hatchery evaluation by paying more attention to chick quality and performance instead of only total chick numbers.

It is also important for us as producers to utilise every opportunity we have to learn from our successes (progeny that excel in the field) as well as our failures (analyzing hatch residue). From this data, we can then analyze our incubation processes to achieve the best results and produce the best quality chicks.
While artificial incubation is a known science that dates back thousands of years, the ‘art of incubation’ is alive and well as the originators of artificial incubation had to be flexible in learning how to accomplish what the mother hen does in a seemingly easy manner. They had to adjust to the conditions they had, much like a mother hen does, and make the necessary changes for the benefit of the soon-to-be hatched chicks.