Research Note: Phosphorus digestibility in conventional canola meal determined using different balance assays

Three experiments were conducted to determine ileal P digestibility and excreta P retention values for canola meal (CM) using 3 different types of balance assays. The first experiment was an ad libitum-fed chick experiment which evaluated the effect of phytase on ileal P digestibility and excreta P retention values. Chicks were fed a P-deficient cornstarch-dextrose-45% CM basal diet (0.13% nonphytate P) as diet 1 or that diet plus 125 or 250 FTU/kg of phytase, respectively, from 8 to 21 D of age. The digestibility/retention of P was 38% and phytase linearly increased both ileal digestibility and excreta retention of P (P < 0.05). The second experiment was a precision-fed chick assay conducted to determine ileal digestibility of P in CM at 21 D. Mean ileal P digestibility was determined to be 47.5% in chicks fed 6 g and 40.0% in chicks fed 9 g of CM and the values were not significantly different. Experiment 3 was an ad libitum-fed chick assay to determine ileal P digestibility and excreta P retention for CM with and without increasing levels of dietary supplemental Ca. The chicks were fed P-deficient - dextrose - CM diets containing increasing levels of 13.5, 27, 40.5, or 54% CM, respectively, with Ca:nonphytate P ratio maintained at 2:1 in diets 1-4 and 6:1 in diets 5-8. Based on regression analysis of ileal digesta or excreta P output on dietary P concentration, digestibility/retention of P in CM was 30%. Ileal P digestibility (and to a lesser extent excreta P retention) at 21 D was reduced by increased Ca:P ratio. The results of this study indicated that the 3 balance assays yielded reasonably consistent values of 30-40% for P digestibility/retention and ileal P digestibility was greatly affected by Ca:P ratio.