Miljøprojekt, 928 – Reduceret fosforudskillelse ved anvendelse af fytasetilsætning svinefoder

Reduceret fosforudskillelse ved anvendelse af fytasetilsætning svinefoder

Summary and conclusions

Phosphorus is an essential nutrient for domestic animals. However, phosphorus is also an actual environmental problem for Danish agriculture. Pig production contributes with about 50% of the total phosphorus amount in manure. Consequently, arable land in regions with intensive pig production is generally supplied with more phosphorus from manure than is taken up be the crops. This means that in these areas large amounts of phosphorus are accumulated in the soil. The accumulated phosphorus might leach into rivers and lakes and may cause eutrophication. Much effort is now attributed to the improvement of phosphorus utilisation in domestic animals.

A major cause for the low phosphorus utilisation is that phosphorus in cereals and seeds is stored in a chemical complex named phytate. Monogastric animals like pigs and poultry are only able to digest and utilise phytate phosphorus to a limited extent. Consequently, it is normal practice to supplement diets for pigs and poultry with extra phosphorus (as inorganic feed phosphates) to fulfil their physiological demand. However, the degradation of phytate is stimulated by the enzyme phytase that is present to some extent in cereals and seeds, but phytase is also available as microbial phytase that can be added to the diets. Phytase is a protein and it can be inactivated by heat treatment, thus loosing its phytate degrading effect.

Research has shown that phytase contributes to improved utilisation of phosphorus in pigs, and addition of microbial phytase to the diets renders phosphorus in phytate more available for pigs and poultry. This means that less inorganic feed phosphate is needed to fulfil the animals' needs. As such, the overall phosphorus utilisation is improved and the excretion of phosphorus is reduced without compromising the animals' requirement. The aim of the present study was to evaluate the effect of addition of phytase to pig diets based on barley and wheat, which are typical components in Danish pig feeds. Furthermore, the effect of heat treatment on phosphorus digestibility was evaluated. The experiment showed that heat treatment decreased the phytase activity, thus reducing the phosphorus digestibility by 8 percentage units, from 57 to 49%. However, addition of microbial phytase to the feed stimulated the degradation of phytate and brought about an increase in phosphorus digestibility to approximately 62% in both heat-treated and not heat-treated diets. This improvement implies that it will be possible to remove 33 to 52 g phosphorus (as mono calcium phosphate) per kg diet. The largest reduction is achieved for heat-treated diets and the smallest reduction refers to not heat-treated pig diets. Assuming that the phosphorus digestibility under practical conditions is improved to 60% as found in the present experiment, the use of phytase will result in a reduced phosphorus excretion of up to 30%.

The overall conclusion that can be drawn from the experiment is that the presence of microbial phytase increases phosphorus digestibility and thereby the utilisation of phosphorus in growing and finishing pigs. However, the magnitude of the effect is smallest in not heat-treated diets (corresponds to on-farm produced diets) and greatest in heat-treated diets (corresponds to commercially produced diets). The intensity of the heat treatment of the diets (temperature, moisture etc.) may affect the results.