Hatchability greatly depends on the fertility of the breeder flock, but storage of hatching eggs is also a major determining factor. Preventing embryonic death is the leading objective, and this depends on various
By Inge Reijrink, HatchTech, Veenendaal, the Netherlands
Storage of hatching eggs longer than seven days causes a delay in hatch time as well as a decline in hatchability and chick quality. Hatchability declines by approx. 1% per day after seven days of storage. The cause of this decline in hatchability and chick quality is, however, not clear. During storage, changes occur in the embryo, and one of these changes is that cells in the embryo die. This can have a negative effect on embryo viability and consequently increase embryonic death.
Cell death can be caused by the length of storage due to aging of the “sleeping” embryo, but it can also be caused by changes in the egg components. During storage the albumen pH increases from 7.6 to 9.0, and albumen height and the strength of the yolk membrane declines. This might be necessary to protect the embryo against micro-organisms, and to improve the diffusion of gasses such as carbon dioxide and oxygen. On the other hand, an albumen pH of 9 might also cause cell death when the embryo is exposed to it for longer times. When cell death is responsible for the negative effect of prolonged storage, we must prevent or compensate it to maintain hatchability and chick quality.
Prevention of cell death
Research has shown that storage temperature influences cell death in the embryo. When storage temperature decreases, cell death decreases as well. Cell death might be reduced because the cells survive better when the temperature is reduced. However, it is also possible that reduced storage temperature reduces the diffusion of gases like carbon dioxide through the eggshell. Because the rise in albumen pH and the decline of albumen height is related to carbon dioxide loss, a reduction in storage temperature delays the changes in the egg components. A slower rise of albumen pH may shorten the time that the embryo is exposed to a pH of 9, and may reduce cell death, therefore improving the viability of the embryo.
Optimal pH for embryo development during early incubation is reported to be 8.2. Perhaps this is also the optimal pH to maintain embryo viability during egg storage. In that case, a rise in albumen pH to 9 should be avoided. This can be done by lowering the storage temperature, but also by storing the eggs in plastic bags to avoid loss of carbon dioxide. Research has already shown that storing eggs in plastic bags can improve hatchability after prolonged storage.
Compensation of cell death
In nature a hen probably compensates for cell death. A hen lays eggs in a clutch, and every time the next egg is laid the previous laid egg is incubated for a short time. During that short time the embryo is able to develop a little bit further and the cells will multiply, replacing the dead cells. In practice, this can be achieved by pre-storage incubation. Although this is expected to be beneficial, reported results are not consistent. The research department of HatchTech Incubation Technology also investigated the effect of pre-storage incubation on hatchability and chick quality after prolonged storage.
Two experiments were conducted. In Experiment 1, eggs from a breeder flock of 28 weeks were stored for 12 days. In Experiment 2, eggs from a breeder flock of 61 weeks were stored for 11 days. Before storage, half of the eggs were incubated for six hours (Experiment 1) or 4.5 hours (Experiment 2). The other eggs were stored immediately. The duration of pre-storage incubation was reduced in Experiment 2, because in Experiment 1 hatchability of fertile eggs was reduced from 80.2 to 74.9%. In the second experiment, hatchability of fertile eggs increased by pre-storage incubation from 80.7 to 85.6%. This again shows that the effect of pre-storage warming can be beneficial or detrimental, and that small changes in the procedure can already cause big differences.
The different results might be caused by the difference in the stage of embryonic development at egg collection (before pre-storage incubation) between the two experiments. At the moment of lay, embryos can be classified in different stages of development. Normally the developmental stage of the embryos ranges from stage VIII to approx. stage XIII (Photo 2). In general, the average stage of embryonic development at moment of lay is stage X (Photo 1). We assume that for optimal storage, embryo development should be in stage XII, but not further. The embryos in Experiment 1 were further developed at egg collection than in Experiment 2. Of the embryos in Experiment 1, 40% were already developed beyond the optimum of stage XII before pre-storage incubation. In Experiment 2, however, the embryos still needed some development to get to this optimum. This might explain the differences in results.
Temperature important tool
The success of pre-storage incubation depends on the accuracy of bringing the embryo in the right stage of development to resist prolonged storage. Embryos that are less or further developed than stage XII are probably less resistant for prolonged storage. The success of pre-storage incubation therefore depends on the developmental stage of the embryo at egg collection and the duration of pre-storage incubation. To optimise the results of pre-storage incubation, the duration should be adjusted according to the developmental stage of the embryo at egg collection to prevent embryos from developing too far. Because the developmental stage of the embryo varies in the field, pre-storage incubation is difficult to use in practice.
In conclusion, pre-storage incubation should be used with care. Accurate compensation for cell death is difficult. We should therefore focus on the prevention of cell death to reduce the negative effect of prolonged storage. Storage temperature is an important tool to prevent cell death and to maintain hatchability and chick quality after prolonged storage!
World Poultry Vol. 25, No. 02