Breed- and age-associated variation in hematological parameters and Toll-like receptor 2 gene expression in peripheral blood mononuclear cells of commercial and purebred laying hens during the laying cycle.

BACKGROUND AND AIM: Hematological parameters and innate immune responses are influenced by genetic background and physiological status, making them valuable indicators of health and immune competence in laying hens. However, comparative information on breed- and age-related variation in hematological characteristics and Toll-like receptor 2 (TLR2) gene expression in PBMCs during the laying cycle remains limited. This study evaluated the effects of breed and age on hematological traits and TLR2 gene expression in commercial Lohmann Brown (LB) and purebred White Leghorn (WL) laying hens to improve the understanding of innate immune regulation during different stages of egg production. MATERIALS AND METHODS: Twenty clinically healthy laying hens (n = 5 per breed × age group) comprising LB and WL breeds at 42 and 80 weeks of age were maintained under identical management conditions. Blood samples were collected for hematological analysis and PBMC isolation. Hematological parameters were determined using standard laboratory methods, whereas TLR2 gene expression was quantified by real-time quantitative polymerase chain reaction. Data were analyzed using a completely randomized 2 × 2 factorial design to evaluate the effects of breed, age, and their interaction. RESULTS: Breed significantly affected hemoglobin concentration, lymphocyte percentage, heterophil-to-lymphocyte (H:L) ratio, and TLR2 expression (p < 0.05). WL hens exhibited higher hemoglobin concentration, H:L ratio, and TLR2 expression than LB hens, whereas LB hens had higher lymphocyte percentages. Age significantly influenced hematocrit, hemoglobin, heterophil, lymphocyte, monocyte, white blood cell count, H:L ratio, and TLR2 expression (p < 0.05). Hens at 80 weeks exhibited higher hematocrit, hemoglobin, lymphocyte percentage, monocyte percentage, and white blood cell count, whereas hens at 42 weeks had higher heterophil percentage, H:L ratio, and TLR2 expression. Significant breed × age interactions were observed for hemoglobin, heterophil, lymphocyte, H:L ratio, and TLR2 expression, with WL hens at 42 weeks exhibiting the highest TLR2 expression. TLR2 expression showed positive correlations with the heterophil percentage and the H:L ratio, but a negative correlation with the lymphocyte percentage. CONCLUSION: Breed and physiological stage significantly influence hematological characteristics and TLR2-mediated innate immune responses in laying hens. The combined evaluation of hematological parameters and TLR2 expression provide complementary biomarkers for assessing immune competence and physiological stress during the laying cycle. These findings establish baseline reference data that may facilitate genetic selection for disease resilience, improve flock health monitoring, and support precision breeding and management strategies for sustainable egg production.