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Interpretive Summary: A comparison of the release of phosphorus by a phytase enzyme in pigs fed diets deficient or adequate in phosphorus content.

By: Dr. Emily Taylor

The majority of P found in plants is unavailable to the pig. However, including phytase in the diet hydrolyzes the unavailable phytate to inorganic P, drastically reducing the need for supplementation. To adequately formulate a diet, it is necessary to quantify the ability of phytase to release P. It has been noted in previous research that the efficiency of phytase differs among diets that are deficient in P when compared to adequate diets.

A study recently published in the Journal of Animal Science further tested the hypothesis that the amount of P released by phytase is greater in diets that are deficient in P. In addition, the authors aimed to determine the effect of phytase on the digestibility of dry matter (DM), gross energy (GE), N and Ca in both P deficient and adequate diets.

Results from the current study supported their first hypothesis that the apparent release of P by phytase is greater in P-deficient diets than in P-adequate diets. Diets deficient in P saw an improvement in P absorption and retention, and also caused an increase in urinary excretions of P. The authors suggest two theories as to why there are different outcomes between diets deficient and diets adequate in P. First, due to P being a carefully regulated system in the body, diets deficient in P could see a proportionate increase in P absorption by the gut. Thus, causing P released by phytase to be absorbed with greater efficiency. Second, a classical feedback loop where the accumulation of P in the intestinal digesta may inhibit the function of phytase causing a decrease in inorganic P of P-adequate diets.

The current study reported P retention levels being significantly higher in P-deficient diets than in P-adequate. Previous research has suggested that pigs will retain P as long as Ca and P levels are balanced in the diet. Authors hypothesized that because Ca levels were kept constant while adding phytase, P levels increased and caused a decrease in the Ca:P ratio. Thus, P retention was lower than expected in P-adequate diets.

In summary, the release of P by phytase was lower in diets adequate in P, and consistent with previous findings. However, Ca availability was increased in diets deficient in P, which is not consistent with previous work. The authors suggest further investigation is needed.

The full paper can be found on the Journal of Animal Science website.