The availability of nutrients in low concentration in diets is difficult to be accessed by means of experiments like apparent digestibility assays. That is because the endogenous contribution underestimates the true availability. The best tool to study the true availability of minerals is the in vivo isotopic dilution technique. Phosphorus (P) and calcium (Ca) are the most studied minerals due to their great importance in animal nutrition. P is one of the most polluting nutrients because of high husbandry concentrations in restricted areas (Tamminga, 1992). There are some remaining doubts concerning the true digestibility of phosphorus. The present study compiles data from previous studies dealing with true availability of different P sources in beef cattle to estimate pollution potential of animal excretions.