How to gauge optimum timing for pulling day old chicks
By Pas-Reform - This article looks at what factors influence the length of the incubation period for day-old chicks.
General principles
The length of the incubation period is influenced by several
factors:
In general terms, 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 21 days of incubation,
while turkey and duck poults 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 -; and
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 is proven 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 ºC. For
chickens, the incubation period increases by 4 hours per
0.5 ºC 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 clearly been shown to
affect chickperformance at farm level.
Source: Pas Reform - April 2006