Genetic differences in eggshell ultrastructural properties of Saudi native chicken breeds kept at high ambient temperatures

Egg quality and eggshell ultrastructural properties of four Saudi native chicken breeds were compared to detect genetic differences. A total of 480 laying hens at 28 weeks of age, representing four Saudi native breeds of chicken (black, black-barred, gray, and brown) kept under hot environmental conditions (34 ± 1°C) were randomly assigned to the current experiment. Laying hens were housed in individual cages in an open-sided house during hot summer season. A total of 360 intact eggs were randomly collected (90 from each breed) for egg quality assessment. Eggshell samples were prepared to evaluate ultrastructural measurements using a scanning electron microscope. No significant variations between the breeds concerning egg weight, egg-shape index, yolk index, albumen (%), yolk (%), shell (%), and shell thickness traits were detected. Brown breed showed significantly higher Haugh units compared to the other breeds. Moreover, brown breed scored the best for eggshell breaking strength trait (the highest crack resistance), followed by gray, black, and black-barred breeds, respectively (P < 0.005). Total ultrastructural score for mammillary layer measurements was significantly higher in black-barred breed if compared with black, brown, and gray breeds. Gray, brown, and black Saudi native breeds had an outstanding eggshell ultrastructure and, in turn, stiffer and stronger eggshell comparable with black-barred counterpart under high ambient temperatures. At the national level, for cross-breeding and selection programs aimed at producing good quality table and hatching eggs the use of gray, brown, and black breeds can be recommended due to excellent ultrastructural properties of their eggshell.