Balancing dietary available phosphorus needs and nutrient excretion of pigs

In trial 1, seven sets of five littermate gilts from a high lean strain were used to determine the dietary available phosphorus needs for high lean pigs fed from bodyweights (± 1) of 7 to 23.5 kg. Pigs fed one of five dietary available P concentrations (0.30, 0.40, 0.50, 0.60, and 0.70%). Protein and fat gain where determined by a deuterium oxide technique. Based on breakpoint analysis, high lean pigs fed from 7 to 23.5 kg bodyweight require daily 5.2 ± 0.6, 5.3 ± 0.9, and 5.0 ± 1.0 grams of dietary available P to maximize body protein gain, efficiency of feed utilization, and body weight gain respectively. Therefore, inadequate intakes of dietary AP lower the pigs\u27 capacity for proteinacous tissue accretion. Trial 2 was performed to determine the effect of closely matching dietary available P with the pig\u27s requirement on nutrient excretion. Dietary P concentrations were lowered from the initial concentrations in an effort to minimize excess urinary P excretion. Once the minimal urinary P excretion was achieved, dietary P concentrations were raised incrementally to the control P concentration. Dietary P concentrations ranged from 0.63 to 0.85%. Based on two slope breakpoint analysis, the inflection point for body P retention per unit of digested P (dP) intake was achieved at an intake of 563 ± 20 mg of dP·kg−1 BW7̇5·d−1. Endogenous urinary and fecal excretion was estimated to be 4 and 5 mg of dP·kg−1BW7̇5·d−1, respectively. At dietary P intakes below the inflection point for maximum efficiency for P retention resulted in 95% retention of digested P intake. Above the inflection point urinary P represented 48.5 ± 5.0% of dP intake resulting 52% efficiency for P retention. Dietary P intakes below the inflection point maximize the efficiency for P retention while minimizing P excretion. This research indicates the maximum efficiency for P retention can be achieved while minimizing P excretion