PSIX-18 Prediction of urinary P excretion as a tool to assess mineral status of growing pigs

Urinary losses of phosphorus (P) and calcium (Ca) are indicators of absorbed compared to amount needed for tissue growth as well as their balance for bone deposition. They can thus be a good indicator of the mineral status. This hypothesis has been validated through meta-analysis using a database of P and Ca retention in growing pigs including 43 publications published between 1969 and 2018 for a total of 51 experiments and 251 dietary treatments. P urinary excretion has been simulated using a multiple regression analysis with the proc MIXED (Minitab® 19) with trial effect as random. Average body weight of the pigs was 32kg ±18kg. Urinary P losses (urineP) was influenced by apparent digestible P (digP, recalculated for each treatment; g/kg), total Ca (Ca, g/kg), and microbial phytase (PhytM, FTU/kg). The model created explains 90% of urineP (R2 = 91%). UrineP was increased with digP from about 2 g/kg of digP (digP, P = 0.02, digP x digP, P < 0.001), before this point it was very low. Increasing dietary Ca decreased urineP linearly when exceeding the 2 g/kg of digP (Ca x digP, P < 0.001); P can then be fixed into bone as hydroxyapatite. The contribution of P is thus to manage in conjunction with dietary Ca. PhytM effect depends of both Ca and P (PhytM x Ca x digP; P = 0.03) showing that phytM addition reduces urineP depending of digP and Ca. As an example, in 6 g Ca/kg diet, 500 FTU/kg addition reduce urineP by 28% in 2 g digP/kg and by only 4% in 4 g digP g/kg. This is due to a better retention of P into bone in low digP. Next step will be urinary Ca modeling and then looking at meaning of their ratio in relation to mineral status to develop a practical tool to assess Ca and P status of pig.