INCLUDING PHOSPHORUS in growing pig diets at 0.5% rather than 0.6% results in a 50% reduction in soluble phosphorus output, according to research at the Agricultural Research Institute of Northern Ireland (ARINI).

Researcher Elizabeth McCann says a study to define the optimum phosphorus requirement of pigs in Northern Ireland compared growing pig diets containing 0.45%, 0.5% and 0.6% phosphorus.

“Production performance was not affected by dietary level of phosphorus, but digestibility and phosphorus excretion figures indicate that the lowest dietary level, 0.45%, resulted in marginal deficiency,” she says. “The highest dietary level, 0.6%, resulted in excess phosphorus excretion in urine. Therefore, the optimum level of phosphorus inclusion in growing pig diets is 0.5%.”

A further study assessed whether including phytase in pig diets would enable them to make greater use of the available phosphorus in cereals in pig diets, says Dr McCann. “Phosphorus is present in cereal diets in the form of phytate molecules and the enzyme phytase is required to break down these molecules. But pigs do not possess phytase, so much of the phosphorus in cereals is unavailable to them.”

In the trial, pigs were offered phytase either in a dry or liquid form. “The results indicate that both methods are effective in improving phosphorus digestibility and reducing phosphorus excretion when used in parallel with a reduction in dietary phosphorus.”

But when phytase is added to diets with adequate levels of phosphorus, the phosphorus released from phytate is not required by the pig and is broken down to available phosphorus and is excreted. This increases phophorus output, so blanket inclusion of phytase is not recommended, says Dr McCann.