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Heat treatment during storage

In the process of incubating eggs on an industrial scale, egg storage is a key element that cannot be ignored or avoided. Long storage times (7 days or longer), however, inevitably lead to a significant decline in hatchability. In order to understand why heat treatment can partially restore hatchability losses caused by egg storage, as well as the limitations to this method, the biology of the early embryonic processes needs to be examined in detail.

By Professor Eddy Decuypere, University of Leuven

The longer eggs are stored, the higher the losses in hatchability (Dymond, 2013). Stored eggs have a higher rate of embryonic mortality between days 2 and 3 of incubation, and need more time to complete incubation. This causes some live chicks to be rejected at take-off because they hatch too late (Nicholson, 2012).

Figure 1: Decrease in hatchability with long egg storage (Aviagen, 2014)

Several studies have investigated the possibility to limit the hatchability loss after long storage by applying short periods of heat treatment during storage, with differing results. In recent years, more and more successful attempts have been reported applying heat treatment during storage, even for large scale trials. Nicholson (2012) and Aviagen (2014) have shown a consistent improvement of the hatchability of long stored eggs (Ross 308 & Ross 708 broiler eggs, as well as various GP & GGP lines) by applying one or more heat treatments in 34 small to large scale trials. Figure 2 shows how the potential for improvement in hatchability increases with storage time.

Figure 2: Improvement in hatchability after heat treatment during storage (Aviagen, 2014)

Effect of storage according to developmental stage

Development of the avian embryo begins immediately after fertilization in the infundibulum and continues as albumen and shell are deposited over the next 24-26 hours. The embryonic developmental stage at the moment of oviposition (egg laying) is variable for different genetic lines as well as parental ages. This may be genetically determined or linked to variations in oviductal transit time and/or body temperature. Anyhow, the effect of long storage times on embryonic development highly depends on the developmental stage of the embryos at oviposition:

Figure 3: Effect of long storage on different development stages after oviposition

It has been reported (Decuypere & Michels, 1992; Deijrink et al., 2008) that embryos at the pre-gastrula stage at oviposition are less able to withstand prolonged storage compared to embryos at the gastrula stage. For these embryos, incubation during storage may improve hatchability, since it can advance them to the developmental stage in which hypoblast formation is complete.

In contrast, if development is already well advanced and embryos have started to form the primitive streak, incubation during storage may be detrimental since it brings the embryo in a more advanced stage of primitive streak formation (period of active cellular migration and differentiation). Storage during such a period could impede critical embryonic processes. So there is some sort of “point of no return”- once this is reached, the embryonic development cannot be stopped anymore.

How does heat treatment during storage help?

In the egg holding room, eggs are kept at or under a so-called threshold temperature or physiological zero for development. However, some partial, but not a global or proportionate development can take place at these subthreshold temperatures. Different cells or tissues in these early embryos may have different threshold temperatures for development, resulting in uneven or disproportionate development. If this disproportionate development progresses too far, it may interfere with embryonic viability and hence also hatchability.

Periodic warming during prolonged storage allows the embryo to redress disproportionate development and ensures the required degree of embryonic development for all tissues in a proportional way.

Figure 4: Effect of heat treatment during storage

In the next E-News, you can read how Petersime has turned this knowledge into practice, bringing you – once again – maximum profit for life. Learn more during VIV Europe (Utrecht, May 20-22nd) at our booth: hall B010 nr 7. Moreover, the method of heat treatment during storage will be further explained during the Incubation 2014 conference on May 19th, to which you are warmly invited.