An experiment was performed as a completely randomized design in a 4 × 2 × 2 factorial arrangement with 4 replicates of 15 chicks in each pen to investigate the effects of flaxseed extrusion and expansion accompanying with enzyme addition in mash or pelleted diets on protein and lipid molecular structure spectral and performance characteristics of broiler chickens. Factors included were four types of flaxseed: control (corn-soybean meal based diet with no flaxseed), raw flaxseed (RF, 200 g/kg), extruded flaxseed (ETF, 200 g/kg) and expanded flaxseed (EPF, 200 g/kg); two levels of carbohydrase enzyme (0 or 25 mg/kg) and two forms of diet (pellet or mash). Performance criteria, protein and lipid molecular structures, blood biochemical characteristics, digestive enzymes activity and nutrient digestibility, cecal microbial population and breast muscle fatty acids profile were evaluated during the trial. EPF increased BW and reduced FCR compared to the RF and ETF throughout the experimental period (0–28 d., P ≤ 0.001). Pelleting the diets increased BW, improved feed consumption and reduced FCR in comparison to the mash diets fed chicks (P ≤ 0.001). Enzyme addition had no impact on BW, FCR and feed intake of chickens. Both EPF and ETF reduced α-helix and increased ß-sheet height and increased CH3 asymmetric stretching compared to raw flaxseed (P < 0.05). Distinct spectral differences were detected between RF and processed flaxseed and also diets containing the processed flaxseed. Digestive lipase and alkaline phosphatase activity were increased when chicks were fed with diets containing EPF and ETF (P ≤ 0.003). Total alkaline protease (APA) was reduced by inclusion of RF. Plasma total protein concentration was significantly increased and triglyceride and HDL cholesterol levels were reduced in chicks fed with flaxseed included diets (P ≤ 0.05). Except for villus to crypt ratio which was increased (P ≤ 0.05) by RF addition, no significant differences were observed in intest
