Increasing Dietary Phosphorus Retention and Decreasing Fecal Phosphate Excretion in Modern Commercial Broilers

Abstract

Phosphorus is a potential environmental pollutant. The objectives were to minimize fecal phosphorus (P) by optimizing the efficiency of utilization of dietary available phosphorus (aP) for carcass and skeletal growth. In two experiments, Arbor Acres X Arbor Acres male broiler chicks were fed from 0-3 weeks of age a diet adequate in vitamin D, calcium (Ca) and P (National Research Council (NRC) 1994). Experiment 1A assessed body weight gain and whole dry skeletal weight at 2,4,6,and 8 wks of age. Experiment 1B used a central composite, rotatable experimental design with dietary Ca from 0.55% to 0.85% and aP from 0.15% to 0.45% from 4 to 7 wks of age. Decreasing the dietary Ca:aP produced a statistically significant (P<.05) increase in %P retention and a decrease in % fecal total P. Experiment 2 used a dietary Ca:aP = 2.0. In 2A, aP varied from 0.25% to 0.4% for age 3-6 wks and 0.25% to 0.35% for age 6-7 wks. There were no effects on body weight or bone ash. Experiment 2B was a P retention, depletion/repletion study from 28 to 45days (d) of age. The 7 treatments varied in dietary aP from 0.25% to 0.40% for age 28-40 d and from 0.30 to 0.45% for age 40-45 d. Measurements were taken from 41 to 45 d of age. Retention of total P and phytate P were significantly increased and total fecal P and fecal phytate P were significantly reduced compared to the NRC-based control treatments when the broilers were fed a P-adequate diet from 40-45 d of age after having been fed a low P diet from 28-40 d of age. Body weight and bone ash were not affected. In conclusion, subsequent experimental designs should evaluate treatments in which dietary Ca and aP would bracket the following values: (1) dietary Ca:aP =2.22, aP=.45% for 1-20 d of age; Ca:aP=2.0, aP=.35% for 20-30 d of age; Ca:aP=1.7, aP=.35% for 30-40 d of age. Repletion would utilize Ca:aP=2.0, aP=.35 until market age.