Study population and incubation

Figure-1 shows the summary of the experimental design executed in this study. A total of 1020 fertile eggs from the Ross broiler breed were obtained from certified distributors in Jordan (Amman, Jordan). The eggs were checked for any abnormality or breakage and 92 eggs were excluded. The eggs were divided into three incubation groups: The control group, the TM using low temperature (TML) group, and TM using high temperature (TMH) group. The eggs of the control group were incubated at 37.8°C and 56% relative humidity (RH) throughout the embryogenesis period, while those of the TM groups were incubated as follows: TML group conditions were 36°C and 56% RH for 18 h/day from days 7 to 16 of embryonic development, and TMH group conditions were 39°C and 65% RH for 18 h/day from embryonic days 7 to 16. RH in the TM treatment was elevated to 65% to prevent excessive water loss from the eggs that might result from their previously elevated incubation temperature.

The summary of experimental design executed in the current study. ED=Embryonic day; n=Numbers; PD=Post-hatch day.

On day 7 of embryonic development, the eggs were examined by candling: The infertile eggs and the eggs with dead embryos were removed. Commercial Type-I HS-SF incubators (Masalles, Barcelona, Spain) were used for egg incubation.