Page 78 - Hand rearing birds second

Incubation 61

forced‐air design, with air circulated by a fan that creates a uniform temperature throughout the
cabinet. Only forced‐air incubation parameters will be discussed here.
Domestic poultry species are normally incubated at 99.5 °F (37.5 °C) and this temperature works
well for many nondomestic species. Particularly large eggs with longer incubation terms typically
require lower temperatures. For example: 96.5 °F (35.8 °C) is typically used for Antarctic Penguins;
98.0 °F (36.7 °C) for condors and other large vultures; 98.5 °F (36.9 °C) for ostrich and large raptors;
and 99.0–99.2 °F (37.2–37.3 °C) for psittacines. The smallest eggs, such as small passerines, and oth-
ers with shorter incubation terms may hatch best at temperatures of 100.0–100.5 °F (37.8–38.1 °C).
If the temperature is a little too high, embryonic development will be slightly accelerated but at
different rates in different tissues. If chicks hatch, they are likely to be reduced in size, have rough
umbilical seals, and be thin and noisy. During hot weather, power failures affecting air condition-
ing may cause overheating in incubators despite the power loss to the machines. Embryos usually
tolerate temporary drops in temperature but not increases in temperature once incubation starts.
An increase of even 1.0 °F (0.5 °C) is often fatal in a few hours or less. If eggs must be moved in an
emergency, such as a machine or power failure, they should always be moved to a machine with
the same or lower temperature. They may be returned to the original temperature once normal
power is resumed.
If the temperature is too low, embryonic development will be retarded, again with different rates
in different tissues if this is extreme or prolonged. It is not usually lethal unless to an excessive
degree or duration, but chicks are often large, sluggish, and sticky with incomplete yolk sac retrac-
tion or partially open umbilical seals. Power failures causing cooling for more than a few hours will
prolong development. Although embryos may survive the initial insult, detrimental effects are
usually not seen until the hatching process is initiated and some late mortality may occur.
During the hatching process for commercial poultry, the incubation temperature is dropped by
0.5–1.0 °F (0.3–0.5 °C) which has been shown to improve hatchability. This seems to work well for
nondomestic species as well, although it has not been scientifically tested.

Humidity
Avian eggs lose weight during incubation, usually 15% ±3%, by water evaporation through the
pores of the eggshell. Because this is a physical process, not a metabolic process, it is not influenced
by the stage of embryonic development and follows a linear pattern throughout incubation. Under
artificial incubation conditions, this weight loss is managed by controlling the humidity in the
incubator.
Domestic poultry are normally incubated at 45–55% relative humidity, at least to start. This is a
good starting point for most nondomestic species. Eggs of species such as ostrich that are from
exceptionally dry climates, however, are incubated without supplemental water in the incubator
and may require a room dehumidifier. Similarly, eggs from wet‐climate species will require higher
humidity from the start.
Eggs should be weighed as soon after laying as possible and weight loss tracked throughout incu-
bation to ensure successful hatching. If the humidity is too high, weight loss will be insufficient
and embryos are likely to be edematous and/or malpositioned or have residual albumen/fluids
(potentially resulting in drowning). Chicks that do hatch may have unretracted yolk sacs and/or
open umbilical seals and will be lethargic. Humidity that is too low will result in excessive egg
weight loss. This causes poor bone mineralization due to impaired calcium transport and weak,
dehydrated (red) chicks with rough/bloody umbilical seals. Ambient humidity is naturally low at
high altitudes and even parent‐incubated eggs may lose too much weight. In this situation, good