If the hatch of fertiles is not as high as it could be, not only the cost of the un-hatched chicken is a negative factor on the bottom line profit. A non-optimal incubation process results in a loss of hatch because embryos are killed by non-optimal climatic conditions. Not only the dead embryos have experienced this climate, a large number of eggs were in the same environment but were able to survive it. These chicks may have survived, but their development was not as optimal as should have been. As a result, it can be expected that the performance of these birds later on will be non-optimal as well. In the field and in experiments we see that the negative influence of the poor incubation conditions on broiler performance is of much higher economic importance than the influence on hatchability by itself.

Artificial incubation

Artificial incubation is a very delicate process that requires an excellent control of conditions to maximize results. During the years, the technology and control equipment used in hatcheries have improved significantly. At this moment, hatcheries setting up to two million eggs weekly are no exception any more, as well as incubators setting over 100,000 eggs in one machine. The technology installed to make this process run constantly and reliable is enormous and complicated. We are able to read and follow all the different machines remotely, control and adjust the settings from central computers, receive alarm warnings by telephone, store and process all relevant data automatically. Modern hatchery management is aimed at creating optimal environmental conditions for eggs and chicks from egg storage at the breeder farm until the moment of chick delivery at the farm. Climatic conditions in any room can be controlled very accurately at any point and at any time.

In spite of all these technical improvements, it can be questioned if we are actually controlling the key factors for the embryo itself to the level that we think we are. Traditionally, incubators are designed to control air temperature in every spot of the machine in a very uniform way. However, the real importance for the embryo is not the air temperature, but the temperature inside the shell, as this temperature dictates the development of the embryo. This means that air temperature control is only adequate as long as it reflects embryo temperature.

A complicating factor in this respect is that an embryo of modern high yielding strains seems to produce much more heat during incubation than the more classical type of birds (Hulet and Meijerhof, 2001). The consequence of this is that the internal egg temperature (embryo temperature) of modern high yielding strains will be higher than of classical strains, if incubator conditions are not adjusted.

Embryo temperature versus air temperature

The embryo temperature, being the temperature inside the egg, is a balance between the heat production of the embryo and the heat transfer between shell and environment. The heat production of the embryo is not a constant factor. As said, high-yielding breeds produce more heat as embryo than classical strains, but also bigger eggs produce more heat. However, the biggest influence has the stage of incubation. During the start of incubation, almost no heat is produced. After about 4 days of incubation we can observe some heat production, which increases to a maximum around 18 days of incubation.

When the eggs should maintain the same embryo temperature throughout the incubation process, the heat transfer has to increase to compensate for the increase in heat production. It is important to realize that this heat transfer is not only a result of the difference in temperature between eggs and surrounding air, but that especially air velocity has a high influence on the transfer of heat as well (Meijerhof and van Beek, 1993). A high air velocity will give a high heat transfer; a low air velocity will give a low heat transfer. This means that when there is a difference in temperature between egg and air, the rate of air velocity will determine the actual embryo temperature at a given moment. Besides air temperature and air velocity, also the evaporation of water and the heat capacity of the air play a role in heat transfer.

Although almost all machines control air temperature very well, the other factors affecting heat loss are much less controlled and vary between and within machines much more. As a result the embryo temperature can vary substantially (Lourens, 2001) and with it the development and the quality of the hatched chick.

Development and chick quality

Practical experience and scientific research shows that trying to control embryo temperatures between acceptable ranges can result in a better hatchability and a better chick quality. Especially he influence on yolk uptake and closure of the navels is high, resulting in differences in first week mortality due to navel/yolk sac infections and e-coli infections. Gladys et al, (2000) showed that a difference in embryo temperature of 2oF resulted in a significant difference in embryo growth and feed conversion of broilers at 6 weeks of age. Wineland et al (2000a and 2000b) demonstrated that differences in embryo temperature resulted in a difference in development of both the whole chicken as well as specific organs.

Incubation is a process of converting the content of an egg into a chicken. The content of that egg supplies both the building stones for the chicken body and the energy that is needed to build up that body. Especially the temperature during incubation influences the process of development and how well the content of the egg is converted into a chicken. Hulet (2001), as well as our our own research indicates that maximizing the development of the embryo during incubation results in better chick quality and especially in a better broiler performance.

How to measure chick quality

A reliable and repeatable measurement for chick quality is important to evaluate and compare the incubation processes within and between different hatcheries and to evaluate changes in the process that are made over time. Many methods have been developed for scoring in a more or less systematic way the quality of a day old chick. Many of these methods are based on a more or less subjective score in terms of viability, alertness, navel quality etc. Although they do give a score of the looks of a chick, it is questionable if these methods are really adequate for measuring chick quality. The goal of a chick quality scoring system should be to have an indicator for the potential performance of the bird in its later life. A scoring system based on the “looks” of a day old chicken doesn’t necessarily give much information about the potential performance of the bird, but probably more about its change on surviving the first week.

As showed by Lourens et al (2004), the development during incubation is related with bird performance at a later age. During incubation, development is mainly influenced during the period in the setter, so the first 18 days. During the hatcher period, non-optimal conditions can have a high influence on the appearance of the day old chick, its navel closure, alertness etc. Roughly the distinction can be made that the setter period is especially important for the later performance of the bird, while the hatcher period is important for its survival change in the first week. Because of the economical impact of the later performance, any chick scoring system should for a large extent focus on the results that are obtained in the setter period, as these methods will show a correlation between chick score and bird performance. Systems that focus mainly on measurements influenced by the hatcher period will have a much lower correlation, if any.

For field trials and hatchery evaluation, we use chick length as an indicator for chick quality. In our own research (Wolanski et al 2003, unpublished results and Luiten, 2003), we found a relative high positive correlation between chick length and broiler growth at 6 weeks of age. When we do experiments or need to look at incubation processes in a more detailed way, we also include navel quality in our observation, but even then 80% of the score is determined by chick length, unless we want specifically to look at the effect of the hatcher.

Literature cited

Gladys, G.E., D. Hill, R. Meijerhof, T.M. Saleh and R.M. Hulet, 2000. Effect of embryo temperature and age of breeder flock on broiler post hatch performance. Int Poultry Sci Forum: 179
Hulet, R.M., 2001. Chick quality, the result of maximizing embryonic metabolism. Avian Poultry Biol. Rev. 12: 189
Hulet R.M. and R. Meijerhof, 2001. Real time incubation temperature control and heat production of broiler eggs. Poultry Science 80, suppl 1: 128
Lourens, S., 2001. The importance of air velocity in incubation. World Poultry 17: 29-30
Lourens, S., H. van den Brand, R. Meijerhof and B. Kemp, 2004. Effect of eggshell temperature during incubation on embryo development, hatchability and post-hatch development. Unpublished data.
Luiten, E. 2003. Size does matters: yolk utilization and chick length as parameter for embryo development. Hybro technical info.
Meijerhof, R. and G. van Beek, 1993. Mathematical modelling of temperature and moisture loss of hatching eggs. Journal of Theoretical Biology 165: 27-41
Wineland, M.J., K.M. Mann, B.D. Fairchild and V.L. Christensen, 2000a. Effect of high and low incubator temperatures at different stages of development upon the broiler embryo. Int Poultry Sci Forum: 180
Wineland, M.J., K.M. Mann, B.D. Fairchild and V.L. Christensen, 2000b. Effect of different setter and hatcher temperatures on the broiler embryo. Int Poultry Sci Forum: 181

Source: Hybro B.V. - March 2005