Inevitable losses of phosphorus in pigs, estimated from balance data using diets deficient in phosphorus.

Faecal losses of phosphorus (P) were determined in 66 growing pigs weighing between 30 and 70 kg on a semi-purified diet containing less than 1.3 g P/kg DM. Regression analysis showed that the coefficient of absorption of P from this diet was 82.5% and that inevitable faecal P excretion of pigs fed this diet was, on average, 5.9 mg/kg BW.d-1 with no statistically significant effect of body weight on faecal P excretion within the range of body weight studied. Semi-purified diets almost identical in composition were also fed to 5 piglets weighing about 20 kg and to 4 heavy pigs of about 150 kg BW. Inevitable daily faecal losses of P were calculated to be 6.2 mg/kg BW in piglets and 6.8 mg/kg BW in the heavy pigs. It is concluded that inevitable faecal losses of P do depend on body weight and that the variation faecal P excretion was too great to allow detecting this effect within the limited range between 30 and 70 kg BW. Further diets were obtained by blending various ingredients into the semi-purified diet. From a total of 262 balances measured under the condition of suboptimal P supply it is concluded that daily inevitable urinary losses of P depend on body weight and, on average, amount to 0.35 mg/kg BW. It is concluded that under the conditions of suboptimal P supply the utilisation of digestible P is almost complete.