Estimation of standardized phosphorus retention for corn, soybean meal, and corn-soybean meal diet in broilers

Two experiments were conducted to estimate standardized phosphorus (P) retention (SPR) of corn, soybean meal (SBM), and corn-soybean meal (C-SBM) diet in broilers and verify the additivity of SPR for feed formulation of broilers. In total, ninety-six 22-d-old male broilers with similar BW were used in each experiment. After 3 d of acclimation, chicks were fasted for 24 h and then fed P-free, corn, SBM, or C-SBM diets, respectively for 4 h in experiment 1 or 72 h in experiment 2. In experiment 1, the results showed that the excreta collection time of 52 h (48 h after feed withdrawal) was adequate for the estimation of SPR. The basal endogenous P loss (EPL) of chicks fed the P-free diet was estimated to be 123±7 mg/52 h per bird. The values of SPR corrected by basal EPL were 37.6 and 50.5% for corn and SBM, respectively. The determined value of SPR of the C-SBM diet was very close (P>0.79) to the predicted summation of SPR from corn and SBM (44.4 vs. 43.5%). In experiment 2, the results showed that the excreta collection time of 96 h (24 h after feed withdrawal) was sufficient for the estimation of SPR. The basal EPL of chicks fed the P-free diet was estimated to be 85.4±4.0 mg/96 h per bird. The values of SPR corrected by basal EPL were 40.2 and 52.9% for corn and SBM, respectively. The determined value of SPR of the C-SBM diet was lower (P<0.001) than the predicted summation of SPR from corn and SBM (39.7 vs. 46.0%), which might be due to the effect of higher total P intake. The results from the current study demonstrated that the P-free diet could be used for measuring basal EPL in broilers and then estimating the SPR values of feedstuffs for broilers. However, the additivity of SPR in the diet formulation needs to be studied further.