Growing pigs inevitably lose phosphorus (P) via faeces and urine even on zero P intake. These
losses depend on the pigs body weight and daily losses account for, on average, 7
mg/kg BW via faeces and 0.4 mg/kg BW via urine. For application in any P evaluation
system for pigs the high variation in P excretion, in particular in faecal excretion,
should be considered. Based on the standard error of estimate, the value for
inevitable faecal P excretion should be increased by 25%, which makes up to a total
of approximately 9 mg P/kg BW inevitably lost per day in faeces plus urine.