Moderate Dietary Lactobacillus acidophilus Supplementation Enhances Mid-Growth Nutrient Utilization and Shifts Intestinal Lactobacillus and Escherichia coli Counts in Yellow-Feathered Broilers

This study tested the hypothesis that dietary L. acidophilus would improve nutrient utilization in yellow-feathered broilers mainly through intestinal changes rather than a consistent increase in growth performance. A total of 195 one-day-old broilers were assigned to a control group (basal diet), a T1 group (basal diet with 10 g/kg L. acidophilus), or a T2 group (basal diet with 15 g/kg L. acidophilus), with five replicates of 13 birds per treatment over 63 days. The biological responses followed a clear pattern. First, supplementation did not significantly affect average daily feed intake, average daily gain, or feed-to-gain ratio at any growth stage or across the entire trial (days 1–63; p > 0.05), indicating limited direct effects on growth. Second, the main nutritional response occurred during days 22–42, when T1 increased the apparent nutrient digestibility of dry matter, organic matter, ether extract, crude protein, and gross energy compared to the control (p < 0.05). Third, intestinal responses aligned with localized gut modulation: both supplemented groups had higher culture-based Lactobacillus counts and lower E. coli counts in the cecum and ileum (p < 0.05), and T1 increased duodenal villus height (p < 0.05). In contrast, serum biochemical, immune, and antioxidant indices showed only isolated, phase-dependent changes and were not considered the primary response. Overall, moderate dietary supplementation with L. acidophilus enhanced nutrient utilization during mid-growth and was linked to targeted intestinal bacterial and morphological changes, but it did not consistently improve growth performance in yellow-feathered broilers.