An experiment was conducted using non-colostomized and colostomized broiler breeder hens to determine the effects of feeding limestone of 2 different mean particle sizes (185 microns and 3490 microns) on P excretion, total P and Ca retention, and urinary P and Ca excretion during a 6-week feeding study. Additionally, changes in plasma inorganic P (iP) and ionic Ca (Ca++) and urinary excretion of P and Ca were determined in one egg laying cycle of 24 hours. One-hundred-fifty non-colostomized and 6 colostomized broiler breeder hens, 30 wk of age, were divided into 2 groups and fed broiler breeder diets supplemented with either small particle or large particle limestone. Two % acid insoluble ash (Celite) was added to the feed as a marker. Diets, excreta, and urine samples were analyzed for total P and Ca by ionic coupling plasma (ICP) analysis. The non-colostomized breeders fed large particle limestone compared to small limestone particles produced a significant increase in percent tibia ash (P < 0.0001) and egg specific gravity (P = 0.0382), but P excretion approached a tendency of being reduced (P = 0.1585). The urinary total P and Ca (˜18 and 9%, respectively) of total P and Ca excretion for breeders fed both sizes of limestone was not significantly different in the colostomized breeders. In plasma, both iP and Ca++ reached a peak during 18 to 20 h and 20 to 24 h post oviposition for smaller and larger particle sized limestone fed groups, respectively. The maximal excretion of urinary P was found during 11 to 20 h post oviposition, whereas urinary Ca peaked during 0 to 11 h post oviposition for both smaller and larger particle sized limestone supplemented groups. In summary, the findings indicate that the particle size (smaller and larger) of calcium source did not significantly influence the quantitative total urinary excretion of Ca and P but did influence the timing of Ca and P excretion.