cjs-200405-0004 ArticleInAPeriodical 2004 Czech Journal of Animal Science 49 5 199-203 LichovnikováM. ZemanL. The effects of a higher amount of iodine supplement on the efficiency of laying hens fed extruded rapeseed and on eggshell quality The objective of this experiment was to study the effects of feeding 6.07 mg/kg of iodine in comparison with 3.57 mg/kg of iodine as a supplement in diets with different levels of extruded rapeseed (4.5, 9.0 and 13.5%) for a period of 52 weeks. The higher amount of iodine had the most marked effect on the egg mass production and on the feed : egg mass ratio when the hens were fed 9.0% extruded rapeseed in the diet. The egg mass production increased from 55.5 ± 1.06 g/d to 57.8 ± 1.12 g/d and the feed : egg mass ratio was improved from 2.15 kg/kg to 2.02 kg/kg. The eggshell weight ratio significantly (P < 0.05) increased in all groups with the higher level of iodine. The higher level of iodine significantly (P < 0.05) increased eggshell thickness in the groups with 9.0 and 13.5% of extruded rapeseed and it also significantly (P < 0.01) increased eggshell strength in the groups with 4.5 and 9.0% of rapeseed in the diets.