There is a global imperative to reduce phosphorous (P) excretion from pig systems. In this study, a previously validated deterministic model was modified to be stochastic, in order to investigate the consequences of different management strategies on P excretion by a group of growing pigs. The model predicts P digestion, retention and excretion from feed composition and growth parameters that describe a specified pig phenotype. Stochasticity was achieved by introducing random variation in the latter. The strategies investigated were: (1) changing feed composition frequently in order to match more closely pig digestible P (digP) requirements to feed composition (phase feeding) and (2) grouping pigs into light and heavy groups and feeding each group according to the requirements of their group average BW (sorting). Phase feeding reduced P excretion as the number of feeding phases increased. The effect was most pronounced as feeding phases increased from 1 to 2, with a 7.5% decrease achieved; the increase in phases from 2 to 3 was associated with a further 2.0% reduction. Similarly, the effect was more pronounced when the feed targeted the population requirements for digP at the average BW of the first third, rather than the average requirements at the mid-point BW of each feeding sequence plan. Increasing the number of feeding phases increased the percentage of pigs that met their digP requirements during the early stages of growth and reduced the percentage of pigs that were supplied <85% of their digP requirements at any stage of their growth; the latter may have welfare implications. Sorting of pigs reduced P excretion to a lesser extent; the reduction was greater as the percentage of pigs in the light group increased from 10% to 30% (from 1.5% to 3.0% reduction, respectively). This resulted from an increase in the P excreted by the light group, accompanied by a decrease in the P excreted by the remaining pigs. Sorting increased the percentage of light pigs that met their dig P requirements, but only slightly decreased the percentage of heavy pigs that met these requirements at any point of their growth. Exactly the converse was the case as far as the percentage of pigs that were supplied <85% of their digP requirements were concerned. The developed model is flexible and can be used to investigate the effectiveness of other management strategies in reducing P excretion from groups of pigs, including precision livestock feeding.

This review summarizes the environmentally friendly methods that are available to manage phosphorus (P) excretion. Phase feeding reduces P excretion up to 10–25% by adding precise amounts of P to broiler diets. Increasing of the Ca:P ratio in diets from 1: 1 to 2: 1 decreased the availability of P from phytic acid. Feeding diets supplemented with vitamin D can increase phytin P (PP) utilization from 31–50 to 68–87%. Total P (TP) excretion by poultry may be reduced by up to 50% through the use of supplemental phytase. Reductions in phytic acid P ranging from 50 to 65% with no decreases in TP of the seed were seen in ‘low-phytic acid’ or ‘high-available P’ (HAP) mutants when phytase supplementation was contained in diet. However, total activity of phytase was 35% higher in the small intestine of laying hens because of different pH. And both microbial phytase and lactic acid enhanced the apparent total tract digestibility (ATTD) of ash, Ca and Mg and apparent ileal digestibility (AID) of phytic acid.