Nutrient absorption in lambs fed diets containing different amounts of phosphorus

Objective. Evaluate the effect of increasing P intake on nutrient digestibility, and compare the true and apparent absorption coefficients of P and Ca in lambs. Materials and methods. Twenty-four Santa Ines sheep, with an average weight of 33.6 +/- 1.6 kg, were distributed into four treatments (0, 2, 4 and 6 g/day of supplementary P) with forage: concentrate ratio of 70:30. The study of apparent nutrient digestibility was conducted during the first week, using the total feces collection method. During the second week, after injection of 7.4 MBq of P-32 and 7.7 MBq of Ca-45, apparent (AAC) and true (TAC) absorption coefficients of P and Ca were determined. The lambs were kept in metabolic cages. Results. The increase in P intake did not affect (p > 0.05) dry matter, crude protein, NDF or ADF digestibility, but the TAC of P and Ca and mineral matter digestibility decreased. The AAC was not affected (p = 0.10). A cubic relationship was observed between P intake and TAC (TAC = 2.16-1.95X+0.55X(2)-0.04X(3); R-2 = 0.38) and linear relationship with the TAC of Ca (TAC = 0.559-0.03X; R-2 = 0.26). TAC and AAC values were different (p < 0.001). Conclusions. The increase in P intake doesn't impact organic matter digestibility, but does affect P and Ca absorption. Apparent digestibility is not a reliable parameter to determine the efficiency of P and Ca absorption.