Modulation of the intestinal microbiota: impact on productive performance and intestinal health in broiler breeder hens.

This study evaluated the effects of different administration protocols of an undefined microbial culture (Normal Avian Gut Flora - NAGF) on production performance metrics, intestinal health, and cecal microbiota composition in Cobb 500 broiler breeder hens during the early production phase (24 to 32 weeks of age). A total of 48,000 broiler breeder hens were allocated across four commercial units, including an unsupplemented control group and three treatment groups receiving NAGF via drinking water at different application frequencies: weekly (Group 1), biweekly (Group 2), and every 21 days (Group 3). Flock performance metrics (egg production and mortality) and macroscopic clinical health scores were analyzed using Generalized Linear Mixed Models (GLMM) for longitudinal repeated measures. Cecal microbiota composition was evaluated at 32 weeks from 20 biological sample pools (n=5 pools/group, derived from 100 hens) via 16S rRNA gene amplicon sequencing. To distinguish statistical significance from practical relevance in this large-scale field trial, biological response magnitudes were prioritized using effect size estimators [Exp(B)]. Administration protocols significantly influenced flock survival and lay performance. The biweekly protocol (Group 2) provided optimal protective efficiency, exhibiting a lower estimated mortality rate than the Control group [Exp(B)=0.753; P=0.012] and superior laying persistence relative to controls. Conversely, extending the administration window to 21 days (Group 3) was counterproductive, resulting in a higher estimated mortality rate [Exp(B)=1.258; P=0.042]. Treated groups exhibited numerical reductions in intestinal gas accumulation and macroscopic lesion scores, although the overall differences were not statistically significant (P > 0.05). Differential abundance analysis using ANCOM-BC confirmed targeted taxonomic shifts, particularly the depletion of potential opportunistic lineages such as Massilistercora and taxa within the order Clostridiales. Collectively, these findings demonstrate that NAGF efficacy is strictly frequency-dependent: biweekly administration optimizes intestinal integrity and flock survival, whereas an extended 21-day interval proves ineffective and should be avoided in commercial health management programs.