General principles

The length of the incubation period is influenced by several factors:

The time needed to complete development from a day-one embryo to a day-old hatchling depends on the species. The chick embryo hatches after 21days of incubation, while turkey poult and ducklings hatch after 28 days. However, within each species, the duration of incubation and thus the pulling time varies between different batches of eggs.

Flock age is also an inherent factor in determining hatching time. Embryos from flocks younger than 30 weeks may need an additional 5-7 hours to complete development compared to older flocks. Incubation time increases again when flocks are older than 60 weeks.

Storage of the eggs also has a major impact on the length of the incubation period, probably because the albumen and yolk undergo physical changes during storage. Prolonged periods of storage are known to be damaging to the early embryo. When eggs have been stored for periods exceeding three days, one hour extra incubation time should be applied for every additional day of storage over three days.

Incubation temperature has proved to be the most important external factor for determining the rate of embryonic development and growth. In turkeys, the hatching time increases by 6-8 hours, depending on breed and flock age, when the incubator temperature is decreased by 0.5°C. For chickens, the incubation period increases by four hours per 0.5°C decrease in temperature set-point. However, it is also important to note that when the incubator temperature is too high, in excess of 39°C (102.2°F) after day 16, the incubation period also increases.

Advice

Given the above information, it is clear that day-old chicks should not be pulled 'on the clock' but rather when the chicks are visually ready for take-off.

To achieve the highest chick quality and most optimum spread of hatch, the time to pull chicks out of the hatcher is when 90-95 per cent of chicks are dry. The last 7-14 chicks per tray (5-10 per cent of the batch) may be wet around the neck. In addition, the optimum time can also be recognized by crushing the empty shells. When the shells are brittle and feel dry, the chicks were pulled at the right time.

When chicks are collected earlier, too many chicks will be classified as second class because they are not completely dry.

When chicks are left too long in the hatcher, the risk of dehydration increases and with it, the risk of mortality in the first week. Furthermore, dehydration of chicks should be avoided at all times because this has been shown to affect chick performance at farm level.

For further information or advice, please contact the Pas Reform Academy.

May 2008