Influence of heat stress and age on the percentage of calcium carbonate in eggshell and the percentage of broken and cracked eggs

Abstract. The influences on eggs of high temperatures and age were examined in hens that were from a poultry farm situated in the south of the Republic of Macedonia where the average summer temperatures were always the highest. The experiment lasted for 9 months and comprised a period of three seasons: summer, autumn and winter. Maximum and minimum temperatures and relative humidity were recorded every day. Layers were of two different ages. During the research, all production parameters were recorded for the flocks: egg production, mortality, feed-consumption, body weight and the percentage of broken and cracked eggs. Once a month 50 eggs out of each age group were examined. An analysis of egg mass, eggshell mass and percentage of calcium carbonate in the eggshell was performed. At the end of the research the results underwent statistically analysis according to the Least Squares Means method. High temperatures in the region had a highly significant influence (<0.01) over egg size, which was smaller than the average. The heat stress showed high significance (<0.01) in relation to the percentage of calcium carbonate in the egg shell, which was lowest in the summer months and highest during the winter months. The age of the layers did not exhibit significant differences in any parameter examined. The percentage of broken and cracked eggs per month was highest in the summer period.