Dietary factors improving eggshell quality: an updated review with special emphasis on microelements and feed additives S. ŚWIĄTKIEWICZ 1 *, A. ARCZEWSKA-WŁOSEK 1 , J. KRAWCZYK 2 , M. PUCHAŁA 2 and D. JÓZEFIAK 3 1 National Research Institute of Animal Production, Department of Animal Nutrition and Feed Science, ul. Krakowska 1, 32-083 Balice, Poland; 2 National Research Institute of Animal Production, Department of Animal Genetic Resources Conservation, ul. Krakowska 1, 32-083 Balice, Poland; 3 Poznań University of Life Sciences, Department of Animal Nutrition and Feed Management ul. Wołyńska 33, 60-637 Poznań, Poland *Corresponding author: sylwester.swiatkiewicz@izoo.krakow.pl The objective of this review is to update and discuss the current findings from studies with laying hens on dietary factors that can beneficially affect eggshell quality, with special emphasis on microelements and feed additives. The crucial importance of dietary calcium, phosphorus and vitamin D 3 levels and sources for eggshell quality has been well documented in scientific literature. Many recent studies regarding the effect of nutrition on eggshell parameters have focussed on dietary micromineral levels and sources. There has been also growing interest in the influence of feed additives on the improvement of intestinal health and mineral availability. The results of the experiments presented here demonstrate that efficacy of layer diet supplementation with microelements and feed additives is not consistent, however findings of several trials indicate, that eggshell quality may be positively affected in certain conditions by optimal dietary level and form of manganese, as well as by the addition of pre- and probiotics, organic acids, and herb extracts. Keywords: laying hens; nutrition; eggshell quality; microelements; feed additives Introduction Poor eggshell quality is a significant problem in the poultry industry, negatively affecting the economic results of egg production, as well as decreasing the hatchability of eggs and increasing embryonic mortality (Hunton, 2005). Protection of the embryo from the doi:10.1017/S0043933915000082 © World's Poultry Science Association 2015 World's Poultry Science Journal, Vol. 71, March 2015 Received for publication June 11, 2014 Accepted for publication September 1, 2014 83