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SUMMARY A study was conducted to determine the effects of a dietary probiotic (a commonly used feed additive) and a posthatch holding time (0, 12, 24, and 36 h posthatching) on the growth performance, blood parameters, and intestinal microflora of male broiler chicks. The study used a 2 × 4 factorial arrangement of treatments. Eight experimental groups were formed by 2 levels of dietary probiotic supplementation [control and a dietary probiotic (Protexin), 0.5 kg/ ton] and 4 posthatch holding times (0, 12, 24, and 36 h). There were 4 replications for each treatment group, with each replication consisting of 20 birds. Depending on the time interval between arrival at the experimental site and feeding, holding chicks before free access to water and feed had a negative effect (P 0.05). A significant decrease in d 10 intestinal pH (P < 0.05) was noted in groups with probiotic supplementation (6.59 vs. 6.42). The number of lactobacilli in control chicks was significantly higher (7.96 vs. 7.13 and 7.28) than that in groups with a posthatch holding time before feeding on d 10 (P < 0.01). In brief, exposure to delayed feed access impaired early growth performance and microbiological measures in the gastrointestinal tract of fast-growing broiler chicks, and supplementing broiler chicks with a dietary probiotic was not an effective tool for ameliorating these negative effects.