Effects of short term phosphorus deprivation on laying hens.

An experiment was conducted to determine the effects on laying hens of ingestion of a phosphorus deficient diet for 6, 9, or 21 days. Four experimental groups consisting of 3 replicates of 5 Leghorn pullets averaging 90 percent egg production were maintained in individual cages. A diet containing corn, soy, and meat and bone meal was formulated to contain 0.39 percent total P on a 90 percent dry matter basis (LP). A normal P diet (NP), 0.64 percent total P, was obtained by supplementation with an inorganic P source. Group 1 (Control) was fed the NP diet for 21 days. Groups 2, 3 and 4 were fed the LP diet for 6, 9, and 21 days respectively. Groups 2 and 3 resumed consumption of NP diet after 6 and 9 days. Individual egg production and egg weight were recorded daily. Individual hen determinations of serum P, g. shell/cm.2 surface area, and feed consumption by replicate were made at 3 or 4 day intervals. The serum P of Group 1 averaged 5.01 +/- 0.31 mg./100 ml. over the 21 days. Serum P was significantly reduced after 3 days of consuming the LP diet. Serum phosphorus of Groups 2,3, and 4 were 2.95 +/- 0.18, 3.03 +/- 0.24, 3.13 +/- 0.32 mg./100 ml. respectively after 6, 9, and 21 days of consuming the LP diet. Serum P returned to control levels within 4 days after resumption of the NP diet by Groups 2 and 3. There were no differences in feed consumption, egg production nor any detrimental effects on egg weight or shell calcification despite the low serum P. Body weight gain of the hens fed the phosphorus deficient diet for 21 days was significantly reduced. At the end of the experiment femur density was determined; the hens which had consumed the phosphorus deficient diet for 21 days had reduced femur density (osteoporous) compared to the control group or the hens fed the phosphorus deficient diet for only 9 days. It is concluded that pullets in 90 percent production can tolerate this low P diet for at least 9 days without apparent detrimental effects.