AFBI to investigate if phosphorus levels in finishing pigs’ diets can be lowered further

Date published: 01 September 2026

Researchers at the Agri-Food and Biosciences Institute (AFBI) are investigating if the level of dietary phosphorus (P) in finishing pigs' diets can be safely lowered to 0.35%, while maintaining productivity.

If successful, the reduction would represent a further significant improvement regarding the environmental footprint of pig production.

Phosphorus is an essential part of a pig’s diet and is fundamental for good bone health and production performance.

However, pigs can only digest a small amount of the mineral present in plant ingredients, meaning that much of it is excreted.

The new research on lowering phosphorus levels will build on previous AFBI work, funded by the Department of Agriculture, Environment and Rural Affairs (DAERA), within the Pig Research Consortium with Devenish Nutrition Ltd, John Thompson and Sons and Preferred Capital Management.

As a result of earlier research, the P in pig diets was reduced from 0.6% to 0.5%, leading to 15% less P being excreted to the environment.

This trial demonstrated that it was possible to lower dietary P safely without impacting on pig performance or welfare in terms of bone strength. The changes were adopted by industry in the early 2000s, resulting in lower P output. 

Later research showed that dietary P could be reduced further by using the enzyme phytase.

Phytase reduced P excretion by 17%, but only when the total P content of the diet was reduced at the same time. Otherwise, phytase can release extra P from feed ingredients that the pig does not need, which may increase P excretion.

Building on these findings and other research, the pig industry adopted a level of around 0.4% total P in finishing diets around 2010. The move from 0.6 to 0.4% meant a 50% reduction in P excretion.

To put the change into context, for a 2,500 finishing place unit, excreted P on 0.6% total diets was 7.2 tonnes. On 0.4% dietary P diets, the P in excretion from the same unit is only 3.6 tonnes per year. 

AFBI is now conducting trials to see if dietary P can be safely lowered to 0.35% through targeted phosphorus nutrition and the use of phytase at higher levels. 

For a 2,500 finishing place unit, excreted P could be lowered to 2.3 tonnes if the 0.35% level is proved to be successful. 

Dr Elizabeth Ball, who leads AFBI’s research on pig nutrition and its impact on the environmental footprint, has also identified that modern pigs retain more P than pigs 20 years ago due to genetics and nutritional strategies. 

The finding is important because it helps identify where there is still potential to reduce phosphorus losses from pig systems. Cutting these losses could save money and reduce environmental impacts.

Dr Ball said: “This research is extremely positive for the environment and a benefit in terms of reducing the land area needed to spread pig slurry. 

“Conducting this research is essential because P is an important nutrient for growth and welfare in terms of bone strength. 

“As with all excretion, it is vital that production efficiency is maintained otherwise P excretion will increase and going too low in P may also result in welfare problems which must be avoided.”