MATERIALS AND METHODS
Incubator
Both experiments were carried out using a Petersime®
incubator, Labo model, containing six blocks with 90o
turning every hour and with a capacity of 900 eggs.
The incubator was provided with hatching space. The
incubator temperature was adjusted according to dry
bulb thermometer and kept constant until the end of
the incubation period. The relative humidity inside the
incubator machine was of approximately 55 ± 2%.
Fertile eggs
Fertile eggs (360 in Exp 1 and 900 in Exp 2)
produced by Cobb® 500 broiler breeders were obtained
from a commercial hatchery, being half produced by
30-week-old breeders, and the other half by 60-weekold
breeders.
Eggshell surface temperature
Eggshell surface temperature was measured by
attaching a thermocouple (cooper-constant) to the
shell with an adhesive tape. The thermocouple was
connected to a datalogger CR10X (Campbell Sci. Inc.,
USA) and the temperature was recorded during the
Effect of Breeder Age on Eggshell Thickness, Surface
Temperature, Hatchability and Chick Weigh
entire experimental period. Data were collected at
every 10 seconds and the mean temperature at every
10 minutes was recorded.
The thermocouple had a precision of 0.05 oC and it
was calibrated by using standard mercury thermometer
immersed in water.