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 <.001), γ-tocopherol (p =.005) and retinol (p <.001) in the yolk. The cholesterol content and n-6/n-3 ratio in the yolk were not influenced by the level of tannins in the diet. A negative effect of tannins was detected in the fatty acid indexes. In conclusion, the inclusion of chestnut wood tannins in the hen diet rich in PUFAs improved eggshell quality, and higher dose of tannin (10 g/kg) increased the deposition of fat-soluble vitamins in the yolk without negatively affecting young hen performance. The tannins increased the eggshell quality and fat-soluble vitamins content in yolks. A dose of 1 g/kg chestnut wood tannins increased the eggshell quality. The increase in fat-soluble vitamins (α- and γ-tocopherol and retinol) content occurred after the addition of 10 g/kg chestnut wood tannins. The dietary tannins changed the levels of myristic, margaric, palmitoleic and eicosenoic fatty acids. Chestnut wood tannins did not affect the performance characteristics. [ABSTRACT FROM AUTHOR]