Biological and economic optimum level of calcium in white Leghorn of second cycle laying hens

Calcium is important for optimum performance and eggshell formation, since inadequate levels in the diet of laying hens may affect shell quality and egg production. An experiment with 250 Leghorn Hy-Line (R) W-98 was conducted to evaluate the effect of five calcium levels (2.74, 3.48, 4.06 and 5.19 % and three laying periods (79 to 87, 88 to 96 and 97 to 105 weeks of age) on egg production and shell quality. There was no interaction between calcium level and laying period, but the main effects showed that: the calcium level of the diet affected (p <= 0.05) daily feed and calcium intake, egg weight, eggshell thickness but not egg mass, feed conversion and egg specific gravity. There were differences among periods (p <= 0.05) in all productive performance and eggshell quality as the age of the hens advanced, except in egg weight. The biological optimum levels for maximum egg mass and shell thickness were 3.17 and 4.02 g hen(-1) d(-1), and the economic optimum level was 3.17 g hen(-1) d(-1).