Impact of Drinking Water Supplemented with Complex Acidifiers on Production Performance, Egg Quality, Physiological and Biochemical Indicators, and Microbial Flora of BIAN Chickens

This study investigated the effects of dietary supplementation with composite acidifying agents containing 2-hydroxy-4-methylthiobutyric acid (≥30.0%), lactic acid (≥24.2%), and phosphoric acid (≥23.8%) on production performance, egg quality, serum biochemistry, intestinal health, and cecal microbiota in 300-day-old BIAN chickens. In a 42-day randomized trial, 900 laying hens were randomly allocated to three groups: the control group (basal diet with tap water), test group A (basal diet with 0.05% composite acidifier in drinking water), and test group B (basal diet with 0.20% composite acidifier in drinking water). The results demonstrated that test group B exhibited a significant 4.6% increase in average egg weight compared to the control (<i>p</i> = 0.029), while test group A showed enhanced Haugh unit values (<i>p</i> = 0.010) and eggshell strength (<i>p</i> = 0.010). Serum biochemical analysis revealed marked improvements in immune function, with test group B showing a 65.49% increase in globulin levels (<i>p</i> = 0.010) and 61.76% elevation in total antioxidant capacity (T-AOC) (<i>p</i> = 0.010). Intestinal digestive enzyme activities were significantly enhanced, particularly in test group A with a 61.73% increase in duodenal lipase activity (<i>p</i> = 0.010) and 37.43% elevation in jejunal amylase activity (<i>p</i> = 0.036). Morphological assessment demonstrated improved intestinal architecture in test group B, with a 26.02% reduction in crypt depth (<i>p</i> = 0.025) and a 44.53% increase in the villus-to-crypt ratio (<i>p</i> = 0.030). Microbiota analysis revealed dose-dependent modulation of cecal bacterial communities, with notable increases in beneficial genera including <i>Akkermansia</i> (from 1.8% to 7.2% in test group A) and Lachnospiraceae (from 4.7% to 9.7% in test group B) while maintaining core microbiota stability. Principal component analysis confirmed distinct microbial ecological niches created by acidifier supplementation. These findings demonstrate that composite acidifying agents effectively enhance egg production quality, immune status, digestive function, and gut health in BIAN chickens, supporting their potential as sustainable alternatives to antibiotic growth promoters in laying hen production systems.