The Ontario nutrients situation is rapidly covered presenting that for a sow in inventory /year, 18 pigs for slaughter are produced. The resulting nutrients excretion for such production is approximately 114 kg of N, 23 kg of P and 70 kg of K excreted in the manure and of those amounts, around 70% of N, 65% of P and 70% of K excreted in the manure come from the grower-finisher pigs. The determining factors for N and P excretion are also presented as being the difference between the supply of nutrients and the animal requirements and attributed to feed usage, amino acids (Aas) and P levels and digestibility, the pigs maintenance requirements, the Aas balance and the retention rate of N and P. Different models that predict the N and P excretion in the manure are discussed. A model based on input/output nutrients would be a good tool at individual pig farm unit to evaluate the nutrient balance.