Increasing eggshell strength and fat-soluble vitamins content in yolk by including chestnut wood tannin in polyunsaturated fatty acid-enriched diet of young hens

The aim of the study was to evaluate the effect of tannins addition to hen diets on the performance and egg quality characterised by the physical characteristics, vitamin content and fatty acid composition of egg yolks. Two hundred and forty 18-week-old Lohmann Brown hens were assigned to three dietary treatments according to the supplementation of chestnut wood tannin (Castanea sativa Mill.; 0, 1 and 10 g/kg) to the diet. The fat source in the diets was rapeseed oil and extruded flaxseed that ensured higher polyunsaturated fatty acids (PUFAs) content in the feed. No effect of tannin addition on the performance characteristics of hens was observed. Both tannin addition treatments (1 and 10 g/kg) significantly increased the shell breaking strength (p = .050), shell thickness (p = .001), shell index (p = .006) and shell percentage (p = .002). The higher level of tannins (10 g/kg) in feed increased the deposition of α-tocopherol (p