True phosphorus digestibility and total endogenous phosphorus losses associated with canola meal for brown laying hens 17 and 32 weeks old

Two digestibility experiments with 48 brown laying hens were conducted using the regression analysis technique to estimate true P digestibility (TPD) in canola meal (CM) and identify if TPD and endogenous P losses (EL) from CM are different in pullets (17 wk) and in laying hens (32 wk). In each experiment, hens were assigned to 4 dietary treatments in a completely randomized design of concentrations of CM (pullets: 350, 525, 690, or 828 g/kg; laying hens: 305, 452, 670, or 790 g/kg). The total collection method was used to calculate P digestibilities. The true P digestibility from CM was 22.9% for pullets and 32.2% for hens. Apparent and true P retentions (%) were not influenced by dietary CM concentrations in pullets, but a linear decrease in true P retention (%) was observed (P = 0.05) in laying hens. No differences in TPD from CM were observed between pullets and laying hens. Differences (P < 0.05) in endogenous P estimates were observed in pullets and laying hens with EL being lower at laying (-344 mg/kg dry matter intake - DMI) than at rearing (-493 mg/kg DMI). The regression analysis technique can be successfully used to measure TPD and endogenous P losses, but its limitations should be considered.