ABSTRACT FOSNAUGHT, MARY HELEN. Mediating Bone Mineral Status in Laying Hens by Feeding Increased Calcium during Rearing and the Lay Cycle. (Under the direction of

Trends to decrease the age of sexual maturity and point of lay without concurrent increases in dietary Ca may reduce the potential for full skeletal mineralization in pullets. During lay, the hens increased genetic capacity to produce more eggs with less feed without respective increases in dietary Ca may further predispose hens to bone weakness leading to welfare and livability issues. Objectives of this research were to evaluate the effect of feeding increased calcium during rearing and the lay cycle as well as strain and density on laying hen performance and bone mineralization status. Pullets were grown to 16 wks in a grow house with 52 pullets/replicate and 28 replicates/treatment (5,824hens total) which were then moved to a lay house from 18-66 wks with either 24 or 36 hens/replicate (at 48 or 64 sq in) so that there was a total of 26 replicates/treatment (5,728 hens total). The 2 x 2 factorial arrangement of treatments during rearing were Leghorns strain: Hy-Line W-36 (H) and Babcock B-300 (B) and Ca:P ratios: elevated (RC+) Ca:P 2.14, 3.14, 4.14 and control (RC) Ca:P 2.14, 2.14, 2.42 ratio of starter (0-6 weeks), grower (6-12 weeks), and developer (12-17 weeks), respectively. In the lay cycle, the 2 x 2 x 2 x 2 factorial consisted of strain, rearing diet, layer dietary regimens: increasing Ca and P (LC+) and constant (LC) and cag