The Artificial-Feeding System with a Lactic Acid Bacteria-Fermented Diet, Compared with Parent Feeding, Is Associated with Tract-Wide Microbiota Shifts and Coordinated Developmental Indices in Squabs

Early-life dietary transition is a critical window for gut microbiota assembly and intestinal maturation in squabs. This study compared the overall artificial-feeding system using a lactic acid bacteria-fermented diet (AF) with a parent-feeding system (PF) during 18-25 days of age. Because AF differed from PF in both diet exposure and feeding ecology, including manual feeding, absence of parental feeding and crop milk, altered feeding rhythm, and potential loss of parental microbial transmission, the objective was to characterize associations between the two systems rather than to isolate the effect of fermentation alone. Squabs were assigned to AF or PF for 7 days. Microbial communities in the duodenum, jejunum, ileum, and rectum were profiled by 16S rRNA sequencing, and body size traits, organ indices, jejunal morphology, muscle histology, serum biochemical indicators, and muscle composition were assessed. The AF system, characterized by lower pH, a higher acid value, and detectable lactic acid bacteria in the feed, was associated with higher alpha diversity in multiple segments and distinct beta-diversity profiles relative to PF. Across intestinal regions, lactobacilli-related genera were enriched, with Limosilactobacillus consistently identified as the most discriminant genus and, together with Lactobacillus, occupying central positions in exploratory co-occurrence networks. AF was also associated with a greater jejunal villus height and villus height-to-crypt depth ratio, larger muscle fiber dimensions, higher intramuscular fat content with increased levels of selected polyunsaturated fatty acids, altered lipid-related serum indicators, and higher organ indices, including the bursa of Fabricius. PICRUSt2 further suggested differences in predicted functional potential related to carbohydrate, amino acid, lipid, and cofactor/vitamin metabolism, although these outputs represent inference from 16S data rather than directly measured functions. Collectively, the AF system was associated with a lactobacilli-centered, tract-wide microbial signature and coordinated intestinal, muscular, and lipid-related phenotypes in squabs, but the findings should not be interpreted as evidence for fermentation alone.