Abstract
Due to the continuous change in climate, thermal stress becomes one of the key factors that interferes with poultry production. This study aims to evaluate the effect of in ovo surface application of Cymbopogon citratus (lemongrass) on the hatching performance, post-hatch morphometric characteristics, and spleen-based immune responses of Gallus gallus domesticus (Rhode Island Red) during thermal stress condition of 39°C. The 90 fertilized eggs were grouped into three: chronic (sprayed with 25%, 50%, 75%, and 100% concentrations), controlled (sprayed with water), and no application groups, which were then assessed using quantitative experimental design. Data was analyzed using one-way ANOVA and post hoc test (Tukey). The study reveals that lemongrass treatment has a varying impact on the hatchability, mortality, physiological traits, and immune response of the chicks. Skeletal characteristics, such as the shrinkage length of the keel, the length of the shank, and wingspan exhibited a great difference between treatments, but body weight, chest circumference, and spleen index exhibited no significant differences. Hence, the surface application of Cymbopogon citratus inconsistently affects chick development and immune characteristics across different concentrations.