Animal microbiomeshavegainedattentionin recent years because oftheirrolesin avariety of physiological responses to disease and environment challenges. In this study, we subjected production white egg layers to a 4-week heatstress challenge to measure changes in the cecal microbiome. We found that heat stress altersthe cecal microbial compositionafter 2 weeks of cyclic heat exposure. To our knowledge, this is the first study to demonstrate changes in microbiome in heat-stressed layers, and provides an approximatetime course for the microbiome alterations.