Effect of Extruded Full-Fat Rapeseed on Egg Quality in Laying Hens

An eight-weeks feeding trial was conducted in 27-wk-old Isa brown laying hens to study the effect of dry extrusion processing on partial reduction in the conmtent of total glucosinolates of locally produced rapeseed and on egg quality parameters. In total, 60 hens were randomly assigned to one of five treatments (CONTROL group, I Exp group, II Exp group, III Exp group and IV Exp group), each comprising 12 individually caged layers. The main composition of the diets was the same, but extruded soya bean seeds were replaced by 1.5%, 2.5%, 3.5% and 4.5% of extruded full-fat rapeseed (EFFRS) in the I Exp, II Exp, III Exp and IV Exp groups, respectively. Rapeseed was extruded together with faba beans. Due to the extrusion process, glucosinolates content was reduced from 14.7 to 6.87 mu mol/g. The results show that dietary treatments did not affect egg weight, albumen height, Haugh units, albumen and yolk pH. However, eggs of laying hens in Exp IV group had a more intensive yolk color, higher redness (a*) and yellowness (b*) indices. The inclusion of EFFRS did not affect egg shell quality parameters, i.e. shell breaking strength and shell index, but in the experimental groups eggs had a thinner shell (P < 0.05). Eggs produced by hens fed diets containing 4.5% of EFFRS had a higher Sigma PUFA/\Sigma SFA ratio and a lower Sigma(n-6)/Sigma(n-3) ratio in yolk lipids than the CONTROL group. A more favourable ratio of n-6: n-3 was determined in egg yolks of the Exp IV group than in the group without EFFRS supplementation. The hypocholesterolemic/hypercholesterolemic fatty acids (h/H) ratio, which is based on the functional properties of fatty acids, was significantly higher in laying hens fed the diet supplemented with 4.5% EFFRS than in the CONTROL group. However, the higher content of polyunsaturated fatty acids in eggs yolk is the substrate of autoxidation and favours the formation of volatile aroma compounds in 28 days stored eggs, by this modifying the sensory quality. So, the results of the conducted trial confirmed that EFFRS (4.5%) is suitable to replace soybean seeds in compound feed for laying hens, but reduces the storability of eggs.