Tags: Hatching | Whitepaper
March 1 2023,
Fertility, which is determined on the breeder farm and is completely independent of what takes place in the hatchery, represents the initial potential of a batch of eggs to produce chicks. Once an embryo forms, it either continues to develop, or it dies. The rate of embryo mortality varies, depending on general conditions such as the age, nutrition and health status of the breeder flock, and the quality of egg handling and incubation. It also varies according to the phase of embryo development.
In this sense, a hatchery plays the role of host, creating the right conditions for embryo development, and the coefficient HOF (hatch of fertile eggs) expresses the quality of the services the hatchery provides. Of course, only fertile eggs can develop and hatch, and their percentage in the batch limits the potential HOS (hatch of eggs set).
In practice, an HOF of 100% can never be achieved. The best batches may reach 96–97%, and over 90% is considered to be good. Surprisingly, HOF – which is the best measure of hatchery-related procedures – is frequently not the main focus of hatchery managers, and HOS, which expresses the economic efficiency of the process, tends to receive much more attention.
To determine HOF, it is of course necessary to know the fertility of a batch of eggs, which means that the eggs need to be candled. Classical candling can be used to distinguish two main categories of eggs:
Modern technology makes it possible to detect a heartbeat, which is of course a clear symptom of life and offers a much more precise distinction. This option, although very attractive, is however not yet commonly used.
Classical light candling can be performed early, on around day 10 of incubation, or at transfer. Early candling is usually applied if the level of fertility is uncertain, for example on eggs from very young or very old flocks or flocks with fertility problems. Most large commercial hatcheries limit candling to transfer alone, when the clears can be removed (manually or using specialised machines) or – if there are not many – transferred together with the live eggs to the hatcher. The empty spaces in the hatcher baskets may then be refilled to ensure a sufficient number of eggs containing live embryos per basket. While obvious ‘bangers’ are removed prior to transfer, contaminated and rotting eggs without visible, external symptoms will often be classified as ‘not clears’ and therefore transferred to the hatcher baskets.
After hatch, the hatcher baskets contain chicks and the hatch debris, which includes various types of unhatched eggs and empty shells. The picture depends on whether or not candling was carried out and with which level of accuracy clears, dead embryos and bangers were removed prior to transfer. If no removal of clears by candling is performed, all of the debris will be found in the hatcher baskets. However, even if candling has been conducted, some clears are usually still found at hatch due to human error or inaccuracies in the automatic devices.
Analysis of the hatch debris provides a useful source of information in the search for improvements. However, a credible analysis must be based on credible information, and the more unhatched eggs are opened, the more reliable this information will be. On the other hand, the size of the sample must be limited to ensure that this necessary but burdensome work remains within reason.
The number of unhatched eggs in a single hatcher basket can vary from around 2–3% to 20% or more of the eggs set. In a good hatch with eggs transferred from the setter without the previous elimination of clears, it could be as low as 7% (approximately 10 eggs in a 150-egg setter tray), which actually means an HOS of 93%. However, such a good result is not standard, and a hatchery that achieves an annual average HOS of more than 85% can be classified as very good. In many hatches, therefore, the result is lower than this and the number of unhatched eggs higher.
To relate the result to the initial number of eggs set, the number of analysed baskets (or setter trays) and their capacity must be known. We need to know whether earlier candling was performed and the proportion of the load that was eliminated before transfer, as only then is it possible to express the collected numbers as a percentage of the initial load.
The dynamics of embryo development mean that it is possible to identify the moment at which an embryo died quite precisely, within a margin of one day. This is however not always necessary in daily hatchery practice, as a hatchery manager is not an embryologist. In large, industrial hatcheries we require quick, simple, mass procedures, and a high number of analysed eggs leading to reliable information counts more than the classification details. What the hatchery manager needs to know is whether the embryo died early, in the first days of the process, in the middle of the process, or at a late stage. This is usually a sufficient accuracy to be able to identify any possible problems. These global categories can of course be fine-tuned if the observed numbers cause particular worry. For example, late mortality can be divided into late setter and hatcher mortality.
For the purpose of analysis, it is preferable to open eggs from the blunt side to classify the contents. To analyse the signs of early development, the fluid content of the egg can be tipped onto a plate, while for embryos in a more advanced stage of development, the embryos should be removed from the shell to assess their shape, size and phase of absorption of intestines and yolk sac. An additional source of information is the shell: this includes the amount of meconium, the moistness of the membrane, the height of pipping and the status of the chorioallantois.
The results of break-out analysis can be compared to a local, hatchery-specific standard based on results obtained in the past, or to the industry standard supplied by the breeding company. An example is given in the table below:
For daily hatchery practice, it is sufficient to categorise the debris into the following groups:
Temperature problems can affect the entire machine or a part of it. If the temperature was permanently too low, embryos will be small and their development retarded. In this case, many will die between day 16 and day 18; their intestines will not be absorbed and the yolk residues will be large. A long period of overheating exhausts the embryos, so that they are unable to hatch. In this case, the embryos are also small, and their internal organs are frequently not fully absorbed. Overheated embryos reaching a more advanced phase and dying in the shell tend to take a position with the head above the wing.
Problems with insufficient egg weight loss are more frequent than those related to dehydration. The air cell is small and the egg content is watery. Embryos therefore die at or before internal pipping or shortly after it, as the amount of available air in the air cell is insufficient and they simply drown inside the egg. The appearance of survivors (full bellies, sometimes in combination with red hocks) can confirm the nature of the problem.
Ventilation becomes increasingly critical after day 15. Embryos that die due to insufficient ventilation are fully developed and can die late, after day 18. The phase of absorption of the intestines and the yolk sac can help to identify when the embryo died.. Absorption of the intestines begins on day 15, followed by absorption of the yolk, which begins on day 18 and continues through day 19 until the point of internal pipping. This difficult process requires an unlimited availability of oxygen, physical power and available space for this extra load inside the body cavity. An exhausted, weak chick with a body full of watery contents cannot absorb the big yolk residue and so complete the process and properly close the navel.
Hatcher mortality is embryo mortality occurring after day 18. Although the embryos die in the hatcher, it can be caused by factors originating much earlier, either during the incubation process or related to conditions in the hatcher. Hatcher mortality is usually an effect of long-lasting problems and cannot be simply ascribed to the conditions at the moment it occurred.
When analysing the hatch debris, as well as focusing on categorising the dead embryos in groups based on developmental stage, the following observations can also be made:
Break-out can be performed in various ways. In a mass procedure, usually applied in very large hatcheries, several people work as a team to open the unhatched eggs one by one and report the results to a ‘secretary’. The data collected is gathered in a continuous database, such as an Excel spreadsheet, which can be used to analyse trends. The break-out results collected during the different phases of the incubation process can be collated, and the resulting analysis makes it possible to identify trends and make comparisons between flocks and with breed or company standards.
If break-out is performed less systematically, a simplified method can be applied. In this case, a sufficient sample of unhatched eggs is opened and categorised on trays by type. For reliable data, the sample should be based on six to 10 hatcher baskets, representing about 1,000 eggs set. Such a physical overview of the analysed debris is worthwhile, as any category that is found to require particular attention can then be rechecked in more detail, additional questions can be formulated and a need for additional data can be expressed.