THE RELATIONSHIP OF CALCIUM INTAKE, SOURCE, SIZE, SOLUBILITY IN-VITROAND IN-VIVO, AND GIZZARD LIMESTONE RETENTION IN LAYING HENS

A 10-d trial was conducted to investigate the relationship of Ca parti cle size (CPS), dietary Ca level (DCL), limestone source (LS), limesto ne solubility in vitro (LST) and in vivo (LS), and Limestone retention in the gizzard (LRG). A total of 120 molted Leghorn hens, 88 wk of ag e, were randomly assigned into a 2 x 3 x 4 factorial arrangement of tr eatments with LS (A and B), DCL (1.95, 3.72, and 5.32%), and CPS of ea ch limestone source (average U.S. Screen Nos. 5, 8, 14, and 27). The i n vitro solubility of the four respective particle sizes were 29.8, 45 .8, 49.3, and 63.1% for Source A; and 36.3, 54.8, 57.7, and 67.6% for Source B. The limestone retention in the gizzard of Source A was great er than that of Source B, The limestone retention in the gizzard was i ncreased as in vitro solubility decreased (P < 0.001) or dietary Ca le vel increased (P < 0.001). The in vivo solubility of the limestone was decreased as dietary Ca level increased (P < 0.001). The in vivo solu bility was negatively correlated (P < 0.05) with ill vitro solubility for Source A when Ca was fed at 3.72%. The data showed that larger par ticle size limestone (> 0.8 mm) with lower in vitro solubility (30 to 50%) was retained in the gizzard for a longer time, which increased th e in vivo solubility (94% maximum). The results support concept that l arger particle size or lower in solubility may increase Ca retention f or layers.