Effect of dietary calcium level on plasma proteins and calcium flux occurring during a 24 h ovulatory cycle

An experiment was carried out to determine whether feeding different calcium levels from the onset of production has an effect on medullary bone reserves, plasma proteins and ultimately shell formation. A total of 80 Single Comb White Leghorn hens photostimulated at 17 wk of age were fed a 2.5% Ca diet until the appearance of the first egg. Thereafter diets providing 2.5, 3.0, 3.5, 4.0, or 4.5% Ca were fed to groups of 16 hens. At 6, 12, 18, or 24 h post-ovrposition, blood was collected from four hens per treatment, which were then euthanized and developing shells and bones sampled. As dietary Ca increased, plasma Ca, protein, and protein-bound phosphorus concentrations also increased (P < 0.05). Dietary Ca level had no effect (P > 0.05) on the % Ca or total Ca content of bone ends or medullary bone. As dietary Ca concentration increased, both shell ash and shell Ca increased (P < 0.05). Regardless of dietary Ca, shell secretion was most rapid during 12–18 h of the ovulatory cycle (postoviposition). Key words: Calcium, medullary bone, shell calcification, plasma proteins