The practice of weaning at 21 days of age has developed considerably in France. The objective of this trial was to study the impact of the age of piglets at weaning (at 21 or 28 days of age) on pig health after weaning under normal or degraded conditions of live. The study was performed in experimental facilities on two batches of 252 piglets from weaning until seven weeks after weaning. A feeding practice with a secure feed during the first 7 days of post-weaning was implemented for pigs weaned at 21 days. Mortality rate was recorded, and diarrhea was assessed by analyzing fecal scores and measuring the dry matter content of the feces. Blood was collected from 160 piglets (to analyze the complete blood count, haptoglobin, antioxidant defense and the production of reactive oxygen species. During the post-weaning period, 47% of piglets were observed to have diarrhea on at least one day, and this percentage was not significantly influenced by age at weaning. The piglets weaned at 21 days of age had a 7-day lag in the onset of diarrhea compared to those weaned at 28 days of age. Animals weaned at 21 days under normal conditions have a higher mortality rate than those weaned at 28 days but not under degraded conditions. These results should be confirmed by other studies.