High ambient temperatures in tropical and subtropical regions adversely affect the growth and egg productive performance of both broiler and laying chickens. Relative humidity and ventilation rate influences bird's performance, particularly when they are reared in open sided poultry houses. Genetic approaches that aid in reducing or altering the extent of plumage cover has, as a result, been adopted in many hot regions. Fortunately, there are some major and marker genes can reduce the deleterious effects of heat stress, naked neck (Na) and frizzle (F) genes being the most notable ones. The bulk of relevant literature has shown that their favourable effects on growth and laying performance are well established. Therefore, the naked neck and frizzle genes can be a viable alternative for broiler and layer production particularly, in the tropical countries where summer temperatures are very high.

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The present research has proceeded on examining the effect of strains in two commercial laying hens (Lohmann LSL and Hi-sex) for Body weight, feed consumption, feed intake and mortality were measured at 28 to 35 wk and egg production traits (egg number, egg weight, Egg mass) which recorded daily from the onset of lay till 65 weeks of age. The egg mass and egg production percentage were significant increased for Lohmann strain than Hi-sex ones. Hi-sex strain was significant more efficient feed conversion (gm egg / gm feed). To assess mechanical eggshell quality a randomly collected 90 eggs for each strain at 35 wk of age, and take twenty samples eggshell randomly from these eggs to examine the ultrastructure of eggshell. The inspection ultrastructure of eggshell for Hi-sex and Lohman strains were appeared insignificant difference ultrastructure variants of eggshell mammillae; the only differences between two stain for length of palisade layer only. The length palisade layer play main role increase eggshell strength for Lohman eggs compared to Hi-sex ones.

Major marker genes are believed to confer not only adaptability to the tropical climate, but also resistance to diseases. During the last two decades, many investigations have observed that naked neck and frizzle genes have favourable effects on immunocompetence in chickens raised under high ambient temperatures. As a result, several tropical countries have introduced these genes in breeding programs to improve both the productive performance and survival rate of chickens.

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