24/10/2018
Eduardo Romanini, Development Department of Petersime Incubators, was in charge of the conference “Imitating Nature, the art of restoring embryonic viability” at the LPN Congress 2018.
In the incubation process at an industrial scale, egg storage is a critical factor that cannot be overlooked or avoided. However, long storage periods (7 days or more) inevitably lead to considerable loss of hatchability.
Storage time and hatchability losses
To understand why heat treatment can partially recover hatchability losses caused by egg storage and the limitations of this method, the biology of early embryonic processes must be examined in detail.
The longer the eggs are stored, the greater the hatchability losses (Dymond, 2013). Stored eggs have a higher embryonic mortality rate between the second and third day of incubation and require more time to complete incubation. This results in some live chicks being rejected at chick removal because they hatch too late (Nicholson, 2012).
Heat treatments and their advantages
Several studies have investigated the possibility of minimizing hatchability losses after a long storage period by applying short heat treatment periods during storage, with heterogeneous results.
More and more successful attempts to apply heat treatment during storage have been described in recent years, even in large-scale trials.
Nicholson (2012) and Aviagen (2014) demonstrate a consistent improvement in the hatchability of long-term stored eggs (Ross 308 and Ross 708 broiler eggs, as well as various grandparent and great-grandparent lines) by applying one or more heat treatments in 34 small- and large-scale trials.
Effect of storage according to the development phase
The development of the avian embryo begins immediately after fertilization in the infundibulum and continues with the deposition of albumin and eggshell for the next 24-26 hours.
The stage of embryonic development at the time of oviposition (egg laying) varies with the different genetic lines, as well as with the age of the breeders. This may be genetically determined or linked to variations in oviductal transit time and body temperature.
In any case, the effect of long periods of storage on embryonic development depends to a large extent on the state of development of the embryo in oviposition:
Critical point during storage
It has been shown (Decuypere and Michels, 1992; Deijrink et al., 2008) that the embryo in the pregastrula state in oviposition supports prolonged storage periods worse than embryos in the gastrula state. In these embryos, incubation during storage can improve hatchability, bringing them to the stage of development where hypoblast formation is complete.
On the other hand, if the development is already well advanced and the embryo has started to form the primitive streak, incubation during storage can be detrimental since it takes the embryo to a more advanced stage of primitive streak formation (migration period active cell and differentiation). Storage in this period could prevent critical embryonic processes.
Therefore, there is a certain “point of no return” reached at which embryonic development can no longer be stopped.
How heat treatment helps during storage
In the cold room, the eggs are kept at a temperature equal to or lower than the so-called threshold temperature or physiological zero of development. However, partial development may occur below these threshold temperatures but not global or proportionate. Different cells or tissues in these early embryos may have different developmental threshold temperatures. So they could develop unevenly or disproportionately. If this disproportionate development progresses too far, it can interfere with the embryo’s viability and, therefore, with its hatchability.
How can we successfully include this treatment in a modern hatchery?
Research indicates that heat treatment during storage must be applied under particular conditions for consistent results. For example, if the frequency of treatment is not precise, the benefits will be limited, or worse, some embryos will develop beyond the ‘point of no return,’ as shown in Figure 5. This implies that the embryos have outgrown primitive line formation and that embryonic development can no longer be stopped. If these eggs are placed back in the egg storage room, their viability will be negatively affected.
Just as important are the absolute temperature and the duration of the transition. For example, figure 2 shows that excessive treatment, for example, heating the eggs too fast or at a very high temperature for a long time, also causes the embryos to pass the point of no return.
Find the right parameters
Genetic companies have made significant progress in identifying the optimum temperature, time, and temperature range for heat treatment during storage.
It is imperative to achieve the proper eggshell temperature. Eggs must be heated to a shell temperature above 32°C; however, keeping the temperature above 32°C for too long will negatively affect hatchability (Aviagen, 2014). Therefore, the heating and cooling phases are another important factor in the process.
Large scale trials
Petersime has used its specialized Re-Store hatchery, with a capacity of 57,600 eggs, to carry out several large-scale trials. In the first phase, tests were carried out with eggs from grandparents’ batches, with excellent results regarding eggshell temperature control, temperature uniformity throughout the incubator, homogeneity in the heating and cooling phases, and recovery of hatchability. The eggshell temperature controlled the internal environment during the entire treatment cycle.
In a second phase, tests were carried out on eggs for commercial broilers. Data on hatchability, chick quality, and post-hatch performance were collected and analyzed during these trials.
In recent trials based on storage for 12 to 15 days, almost complete recovery of losses was obtained, both in terms of hatchability and final post-hatch weights. This confirms the great potential of the heat treatment methodology.
General conclusion
Heat treatment during storage has great potential to restore embryo viability, recover hatchability, and even improve post-hatch performance. However, it is essential to precisely control the critical incubation parameters since an inappropriate application of the technique could imply sub-optimal results and cause significant losses.
Good practice includes precise measurement and control of the eggshell temperature in the hatchery, as well as controlled and uniform heating and cooling phases of the eggs: Two key points for consistent profits.
-The references are available upon request.
