AimsThe objective of this study was twofold: (i) to examine the effect of early-posthatch dietary inclusion of the clay mineral palygorskite on laying pullets' growth and (ii) to determine the potential effects of the latter diet on caecal microbial communities. Methods and ResultsFour hundred and thirty-two female, 1-day-old Hyline Brown chickens were equally and randomly allocated to two dietary treatment groups; control and palygorskite (0 and 05% palygorskite respectively). They were reared in floor pens for 18weeks. Feed intake, feed conversion ratio, body weight gain and uniformity were assessed. At the end of the rearing period, 53 birds per group were transferred to laying cages without any changes in their respective dietary treatments. At onset of lay, eight birds from each group were euthanized and their caeca were obtained for analysis. Culture-independent and sequencing-based methods were used to analyse caecal microbial composition. ConclusionsPalygorskite dietary supplementation increased the uniformity of the relative group at the end of the rearing period. Pullets that received palygorskite had different and more homogeneous caecal microbial profiles at onset of lay when compared to controls. Moreover, in the caeca of the former pullets a more favourable microbiota was evident; it comprised largely of bacteria that are major degraders of resistant polysaccharides and efficient in butyrate production. Significance and Impact of the StudyThe novelty of this study lies to the beneficial effect of palygorskite (a clay mineral) to pullets growth and health, likely through modulation of the gut microbiota.