Intestinal microbiota and metabolic biomarkers of subclinical gastrointestinal dysfunction in Lohmann sandy laying hens

This study presents the results of a comprehensive investigation of Lohmann Sandy laying hens aimed at evaluating the diagnostic value of productive, microbiological, hematological, and biochemical parameters for the detection of subclinical gastrointestinal disorders during routine flock health monitoring. The study was conducted under commercial production conditions using two groups of birds (n = 15): a control group of clinically healthy laying hens and an experimental group showing signs of functional gastrointestinal disturbances. The experimental group exhibited a significant decline in laying performance, from 93.2 ± 0.8 % to 85.6 ± 1.2 % (P < 0.01), while the average egg weight decreased from 62.5 ± 0.9 g to 59.8 ± 1.1 g (p < 0.05). Feed conversion ratio deteriorated from 2.15 ± 0.05 to 2.38 ± 0.07 kg per 10 eggs (P < 0.05). Clinical manifestations were nonspecific and included depression, poor feather condition, and altered fecal consistency. Hematological findings reflected activation of the nonspecific immune response. The leukocyte count increased to 26.2 ± 1.8 × 10⁹/L (P < 0.05), the proportion of heterophils increased to 36.0 ± 3.0 % (P < 0.05), whereas the percentage of lymphocytes decreased to 54.0 ± 2.0 % (P < 0.05). Consequently, the heterophil-to-lymphocyte ratio (H/L ratio) increased to 0.67 ± 0.04 (P < 0.01). Microbiological examination confirmed the development of intestinal dysbiosis, characterized by an increase in Escherichia coli counts to 10⁵–10⁶ CFU/g, compared with 10¹–10³ CFU/g in clinically healthy hens, together with a reduction in the populations of Lactococcus spp. and Bifidobacterium spp. Biochemical analysis revealed a 9.9 % increase in total protein (P < 0.001), a 17.8 % increase in albumin (P < 0.001), a 7.5 % increase in globulin (P < 0.05), and a 14.6 % increase in inorganic phosphorus (P < 0.001). In addition, the calcium-to-phosphorus (Ca/P) ratio decreased by 10.1 % (P < 0.001). Correlation analysis demonstrated significant relationships between the intestinal microbiota, biochemical parameters, and productive performance. A positive correlation was observed between E. coli counts and globulin concentration (r = 0.720), whereas negative correlations were found between E. coli counts and the albumin-to-globulin (A/G) ratio (r = -0.685) and between phosphorus concentration and the A/G ratio (r = -0.610). In contrast, a positive correlation was identified between the protein coefficient (A/G ratio) and laying performance (r = 0.650). The findings indicate that subclinical gastrointestinal disorders in laying hens primarily develop as a dysbiotic process, accompanied by moderate systemic metabolic alterations and reduced productive performance. The results support the implementation of comprehensive flock health monitoring, with particular emphasis on the intestinal microbiological profile, production performance indicators, and selected metabolic biomarkers.