Re-evaluation of calcium and phosphorus requirements of laying hens for optimum performance and eggshell

ABSTRACT A long-term experiment was conducted to re-evaluate the Ca and available P (AP) requirements of laying hens for optimum performance and eggshell quality. The experiment lasted from 20 to 64 wk of age and was divided into three phases: Phase 1,20 to 36 wk of age; Phase 2,36 to 54 wk of age; and Phase 3,52 to 64 wk of age. The treatments (T) consisted of diets with 3.5 to 5.5% Ca in increments of.5 % and a constant level of AP (.4%) (Tl to T5); a step-up Ca phase feeding regimen of 3.5, 4.5, and 5.5 % with a constant level of AP (.4%) (T6); a step-down AP phase feeding regimen of.4,.3, and.2 % with a constant level of Ca (3.5%) (T7); a concurrent step-up Ca phase feeding and step-down AP phase feeding regimen with or without substitution of 50 % oyster shell for pulverized limestone (T8 and T9); and a regimen similar to T9 with a step-up cholecalciferol phase feeding of 2,200,4,400, and 8,800 ICU/kg (T10). Increasing the dietary level of Ca did not have any beneficial effects on shell quality, indicating that the National Research Council (1984) estimated requirement of 3.75 g Ca per hen per day is adequate for optimum shell formation. A step-u