Uniform Embrionic Development: "in the Hen and in the Incubator"

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The production of poultry meat is more and more organized in large scale poultry integrations including the breeder farm, hatchery,  roiler farm and processing plant The economics of the integration depends on the results of the separate links in the production chain but is determined by the effi ciency of the weakest link. The higher the level of integration the higher the demands placed on skills of the  separate managers.

The economics of today’s poultry production chain also depends on uniformity al all levels of the production chain In the context of this paper the term uniformity is a paraphrase of a good quality product of equal sizes without specifying any quantitative aspects. Uniform
breeder fl ocks produce uniform eggs, uniform eggs produce uniform day old chicks and uniform day old chicks produce uniform broiler at slaughter weight. 

Is it really as simply as that: does uniformity in one link of the production chain automatically results in a uniform product in the next link The answer to this question is: no It is obvious that the quality of the equipment and management influence uniformity of the products at each level. This statement lays not only a heavy burden on the shoulders of the modern hatchery manager but also on the producer and developer of modern incubators In this paper I will address management and equipment related factors which highly influence the uniformity of chicks at day 7 of age. 


The growth rate of the embryo is primarily determined by the temperature in the incubator. The levels of oxygen/carbon dioxide (=ventilation) can become limiting during the second half of the incubation period when the growth is exponential and thus the need for fresh air, oxygen, is highest. The humidity in the incubator controls the weight loss of the eggs. High levels of relative humidity prevent the evaporation of metabolic water and thereby hamper optimal growth of the embryo High levels of humidity in the hatcher block the hatching process because the volume of the air cell is too little. 

Dehydration of the eggs and embryos must be prevented at all times and thus appropriate humidity levels of 50-53% should be applied. Constant levels of humidity support the linear weight loss and thereby a natural acid-base and ion-balance between the embryo and the different extra-embryonic fluid compartments. 

The climate in the  incubator not only determines the number of embryos that fi nally hatch, but it is becoming more and more accepted that the climate have a major impact on chick vitality and performance. The modern hatchery manager is focussed to deliver batches of uniform chicks that will grow at their greatest genetic potential and does not accept incubators with poor and unreliable climate controls. The challenge for the producers of equipment is to design incubators that can control the climate as accurate and homogeneous as possible. These statements put high demands on the design of the modern single stage incubator.


Ideally the manufacturer of hatchery equipment follows trends of the market carefully and is thus aware that the demands of today’s markets develop towards a more uniform product. One trend that cannot be overlooked at, is the change from multi-stage to singlestage
incubation Except for the advantage of proper cleaning and disinfection after each incubation cycle, single stage incubation offers the opportunity to support the embryo with the optimum incubator climate at each stage of development.

To achieve the goal of incubation towards uniformity the design of incubator must comply with strictest requirements of climate control The highest possible uniformity for each batch of eggs is achieved if the design of the incubator is based on small units not larger than the average size of the batch of eggs. Since the average breeder house is 20 000 chicken breeders this means that size of the unit must be somewhere in between 18 500-19 500 eggs Obviously the climate is controlled per unit and thus each batch of eggs follows its own incubation program The climate per batch of eggs is as homogenous as possible.

In addition to the basic design, the incubator must be provided with a the climate control that is flexible and operation friendly such that the hatchery manager exactly knows the reaction of the incubator climate upon changes in set points of temperature, ventilation
and relative humidity To achieve the highest incubation uniformity the climate controller must be extended with a preheat function and programmable turning facilities.


The management of the hatchery should be focused to produce routinely batches of uniform chicks. This means that attention must be paid to every small detail, from the temperature during egg transport to the maintenance and calibration of the equipment. In addition the management must have the attitude of continuously improvements and, thus, keeps records, analyse and adjust. If hatchability and/or chick vitality is below the standards the management has the knowledge and tools to solve these problems One of those tools to solve problems is an open communication between all the links of the poultry production chain But firstly, the hatchery manager must receive good starting material: hatching eggs of high quality. 

Breeder farm

One of the details to look at is the uniformity or quality if hatching eggs The uniformity of a batch of eggs is seen at the first glance:  colour, size and form are similar for all the eggs in a batch. The batch of these eggs derives from one flock and is from one production date, information which can be read on the egg receipt form. A uniform batch of egg does not contain cracked eggs nor dirty fl oor or washed eggs. These second class eggs are not intended to be put in the incubator. However the fraction of second class eggs produced  gives the hatchery manager information about the health of the fl ock and quality of breeder farm management. Thus if uniformity is the goal, the hatchery manager needs to have insight in the numbers and quality of all the eggs produced The information on the egg receipt
form, if fi lled in correctly, forms an essential part in the communication between the hatchery manager and the breeder farm.

Egg quality

Once arrived at the hatchery, the second class eggs are separated from the first class hatching eggs. The second class eggs might be sold as industry eggs or placed in a separate incubator. The first class eggs are either set immediately or the stored in the storage room for placement later. The eggs might be disinfected either shortly before placement of eggs in the setter or before storage. However, for uniformity batches of eggs should not be mixed, independently whether the eggs are stored or placed immediately An important detail in the management towards uniform chicks is the logistics of storing and placing eggs: batches of eggs must not be mixed but sorted such that one unit in the incubator can be filled with one type of eggs: same breed, same flock age and similar days of storage. 

Uniformity and management: incubation

The temperature determines the rate of development and thus, for uniformity, eggs must have a uniform temperature at the start of incubation. For this the preheat function and subsequently a fast and homogeneous heating of the eggs to an egg shell temperature of 100 ºF are essential functions of of the setter. The length of the hatching period, hatch window, is determined by the level of  homogeneity of the egg temperature during the first week of the incubation. The homogeneity of the egg temperature is an egg as well as an incubator dependent parameter The design of the air fl ow and automotive climate control in each unit of the incubator defines the even spread of heat towards the eggs The uniformity in egg sizes determines the time needed to warm the internal contents of the eggs, larger eggs need longer times than smaller eggs.

Hatch window 

The hatch window is defined as the time period between the hatching of the fi rst chicks and the last chicks If uniformity of chicks is the goal than the hatch window must be as narrow as possible because only then the hatchery manager is able to exactly control the pulling time. Thus, for uniformity, the hatch window only depends on the physiological variation between the eggs and embryos placed in one unit of the incubator. The physiological variation between the eggs is determined by breed, maternal age and storage conditions. For example, storage of eggs will increase the variation in embryo quality at the start of incubation and consequently the width in hatching period. In conclusion, a narrow hatch window is essential if the hatchery manager goes for uniform chicks. The details to look at are the uniformity of eggs set, the homogeneity of incubation climate, a uniform cooling period during transfer and an automatic controlled humidity profile during the hatching. 

The brooder period 

We extend the hatchery with the first week in the farm because it is more and more common to consider the 21 days of incubation plus the first 7 days as the most crucial period of birds life and performance. This is true, although at fi rst sight the day old chicks look like independent individuals that can eat, drink and make noise But after hatching the maturation of the different tissues and physiological feedback/control systems, started during the last week in the incubator, continues. The environmental conditions during the first week define, through epigenetic adaptation, the set points of these physiological control systems Stress of all sorts during this period might affect the growth and performance of the chicks irreversible. 

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