The introduction of an extra feed (phase feeding) during the production cycle leads to 2 to 10% reduction of P and N excretion in the manure. With the use of microbial phytase, the digestibility of P can be improved by 20% or more resulting in less or no P supplementation for growing and pregnant sows and a reduction of P excretion from 20 to 30%. The excretion of N can be lowered by 20% by the incorporation of synthetic amino acids and lowering the crude protein level in the diet by 2%. Most of those options leads to an increase in the price of the mixed feed. More constraints may come later for copper, zinc and potassium.

This article is very complete and thorough with the implication of the pig nutrition and environmental pollution.