Short- and long-term sex-dependent effects of a nutritional supplement after hatching on growth, metabolism and gut microbiota in broiler chickens.

1. In chicken production, a delay occurs between hatching and placement in the rearing building. This work analysed the effects of this experience on growth, metabolism, and caecal microbiota and tested whether a nutritional supplement (SUP) could mitigate these effects.2. Chicks were placed directly in a rearing room (Control: C) or were exposed to a 24 h period without feed and water before being placed (Delayed: D). During the 24 h period, half of each group was provided with a SUP.3. The D effect reduced body weight until d 27 in females ( = 0.017) and d 34 in males ( = 0.015). On d 1, the D group had reduced plasma triglycerides (TG) and increased uric acid (UA), total antioxidant status (TAS) and liver thiobarbituric acid reactive species in both sexes ( < 0.050). On d 34, the D group had increased UA and TAS only in females. It increased the α-diversity of microbiota in males (d 12  = 0.036; d 34  = 0.038) and the α-diversity in females on d 34 ( = 0.008). Changes in microbiota composition in both males and females were observed until d 34 at the genus level.4. On d 1, the SUP increased glucose concentration in D and C group males ( = 0.001) and females ( = 0.002). The decrease in TG and increase in UA concentrations and TAS in chicks from the D group were mitigated by the SUP in females. On d 34, SUP reduced the haptoglobin-like activity in D and C group males ( = 0.041) and increased the TG concentration in C group males ( = 0.016). The SUP had little effect on the caecal microbiota.5. Delayed placement induced long-lasting effects on growth, metabolism, and caecal microbiota composition. The effects of a nutritional supplement were variable and sex-dependent.