A MATHEMATICAL-MODEL FOR ESTIMATING THE AMOUNT AND COMPOSITION OF SLURRY FROM FATTENING PIGS

A mathematical model to estimate the amount of slurry and its dry matter, nitrogen (total and ammonium), phosphorus, calcium, magnesium and potassium content is described. The input variables of the model are: animal weight and growth, water intake (including spilled water), amount of cleaning water used, feed intake and composition, ambient and slurry temperature, amount of inoculation material and the storage time of the slurry. The model can quantify the influence of different practical situations on the amount and composition of slurry from fattening pigs. Calculated values of model parameters are compared with results from literature. Calculated values of output variables are compared with results from balance trials. It is concluded that the model can make a good prediction of the amount of different components excreted by the animal. In future more attention should be paid to water evaporation from the animals and from the pigshed and to validating the formulas that describe anaerobic digestion in the slurry.