In spite of the large amounts of money invested in research, breeding, and the improvement of commercial egg-type strains, high environmental temperature (HET) has been identified as a major non-genetic constraint limiting expression of their full genetic potential. This environmental stressor has been implicated in adverse marked effects on egg production and eggshell quality of hens. Reports have conclusively indicated that poor performance (i.e. drop in egg production and poor eggshell quality) of layers reared in thermally-stressed environments could be adduced to a complex interplay of low feed intake, malfunctioning of the endocrine system, acid-base imbalance and poor physiological functioning of organs and mechanisms connected with the entire egg production process, via follicular recruitment and growth, ovulation, egg formation, shell formation, egg development, oviposition and oviposition interval.
