Impact of early phytobiotic and prebiotic supplementation on growth performance trajectories in broiler chickens: a time × treatment interaction study

This study evaluated the effects of early dietary supplementation with phytobiotic (nettle flour) and phytobiotic–prebiotic (alfalfa flour) additives on the growth performance of Ross 308 broiler chickens. A total of 90 one-day-old chicks were allocated to three dietary treatment groups (control, nettle, and alfalfa), each consisting of 30 birds in three replicates of 10 birds. Feed additives were administered during the first 7 days post-hatch, followed by a common basal diet across all groups until day 35. Body weight was recorded on days 7, 21, and 35. Statistical analyses included one-way ANOVA, two-way ANOVA with interaction, Ordinary Least Squares (OLS) regression, and Welch's ANOVA to account for heteroscedasticity and non-normal distributions. Significant treatment effects were observed at all time points, with a marked divergence emerging by day 35 (F(2, 87) = 138.78, p < 0.0001). Post-hoc analyses confirmed that nettle flour led to the greatest increase in body weight compared to both the control and alfalfa groups (p < 0.001). The alfalfa group exhibited a moderate but statistically significant effect (p < 0.05). Two-way ANOVA revealed a strong treatment × time interaction (F = 90.93, p < 0.0001), indicating that the efficacy of the additives varied across developmental stages. OLS regression confirmed the robustness of the model (R² = 0.957), with the "Nettle × Day 35" interaction contributing an estimated +715 g gain in body weight over the control. These findings highlight the potential of short-term early phytobiotic and prebiotic supplementation to produce long-term enhancements in broiler growth performance. Nettle flour, in particular, demonstrated superior efficacy, suggesting its potential as a functional feed additive in intensive poultry systems.