This study evaluated the health effects of feeding diets of different feed particle sizes supplemented with multienzyme to broiler chickens. Cobb500 (n = 450) broiler chicks (as hatched) were randomly distributed to nine treatments, with each treatment consisting of five replicates of ten birds. The experiment was arranged in a 3 × 3 factorial (three feed particle sizes [3, 4, and 5 mm] and three multienzyme supplementations [0, 1, and 2 g/kg]). The blood indices of the chickens were evaluated. The data were subjected to Analysis of Variance (ANOVA), and means were compared using the Tukey Test at a 5 % probability level. The correlation between the growth performance and blood indices was also calculated. Birds fed the 3 mm particle sizes had decreased (p < 0.05) red blood cell (RBC) and lymphocyte counts with increased multienzyme at the starter phase, while the other haematological indicators increased as the multienzyme supplementation increased. Feeding the 4 mm particle size yielded similar (p < 0.05) total protein, triglyceride, and uric acid for all multienzyme inclusions. An increase in the multienzyme inclusion increased (p < 0.05) the RBC of birds fed the 5 mm particles with a decreased (p < 0.05) white blood cell (WBC) and eosinophil counts. At the finisher phase, serum albumin increased (p < 0.05) while alkaline phosphatase (ALP) decreased (p < 0.05), with increased multienzyme inclusion in birds fed the diet of 3 mm particles. Birds fed 4 mm particles had increased (p < 0.05) ALP and high-density lipoprotein (HDL) with increased multienzyme, while those fed the 5 mm particle size had increased (p < 0.05) albumin, aspartate transaminase (AST) as multienzyme supplementation increased. The correlation between growth performance and blood indices showed that feed intake (FI) has a significant (p < 0.05) impact on the blood profile of broiler chickens. The study concluded that other growth performance indicators, except the feed intake, have no impact on the blood profile of broilers. Feed particle sizes impact feed intake in broiler chickens which consequently impacts their blood composition. Therefore, the size of broiler feed particles has an impact on the health and well-being of the birds.
