Relationship between egg shell breakage and laying hen housing systems - an overview

Egg shell breakage is and remains a source of economic loss to the egg producer. In general, about 3% of the eggs laid by hens housed in battery cages or in free-run systems have cracked shells. This number increases about another 1% for hens kept in enriched cages or housed free-range and a further 1 to 2% for those in aviaries. The range of cracked shells reported was from 2 to 12%, but there were few published reports for most production systems. The occurrence of dirty-shelled eggs is about 2 to 3% higher than the incidence of eggs with cracked shells. Shell breakage is also influenced by manufacturer of enrich cage systems. The highest impact eggs receive as they move from the hen to the retail store is in the laying house; overall, eggs receive impacts that average about 13 G. The material used to make egg cartons (paper pulp or plastic foam), the cases in which the cartons are shipped (cardboard or wire), and the location of a carton within the shipping case (top, middle or bottom) affect the occurrence of shell breakage when eggs are transported. Even apparently weak impacts to egg shells may cause microcracks to develop and if the impacts are stronger visible cracks become apparent or they may rupture the mammillary membranes which will allow the egg's content to escape.