Effects of calcium and phase-feeding phosphorus on production traits and phosphorus retention in two strains of laying hens.

Three levels of dietary Ca (3.0, 3.5, or 4.0%) were fed throughout a 336-day experiment to two strains of Single Comb White Leghorn hens in a factorial arrangement with three P feeding programs: .64% P fed continuously; .56, .49, and .39% P; or .64, .54, and .44% P fed when hens were 24 to 36, 36 to 52, and 52 to 72 weeks, respectively. In addition to production traits, measurements of P retention were made at 34, 42, 50, 62, and 72 weeks of age. No dietary effects were observed on production traits. Average P retention over the entire experiment was 104, 148, and 178 mg/day when hens were fed 3.0, 3.5, and 4.0% Ca, respectively. Most of the favorable effect of Ca on P retention occurred after 50 weeks of age. However, increasing dietary Ca had an adverse influence on P retention at 42 weeks, when ambient temperature was unusually hot and feed intake decreased markedly. Significant P effects were observed when hens were 42 and 72 weeks of age. At these times, hens fed .64% P retained the most P while those phase fed .56, .49, and .39% P retained at least. Retention of P tended to decline with increasing age of the hens. Overall, the hens were in a state of marginal to negative P balance at 42, 62, and 72 weeks of age even when P deposited in eggs was considered.