Pigs can utilise more of the phosphorus in their feed if plant phosphorus digestibility is improved. This would benefit not only the pig but also the environment because not as much excess phosphorus would end up in the manure.

The majority of plant phosphorus in pig feed is present in the form of phytate but pigs utilise the phytate-bound phosphorus poorly. To rectify this, the enzyme, phytase, is added to the feed but even with this additive the digestibility of plant phosphorus is only 60 to 65 per cent. Scientists from Aarhus University have investigated why this is the case. So far, they have found that the phytase does not have enough time in the pig stomach to break down the phytate-bound phosphorus sufficiently.

Important nutrient

Phosphorus is an important nutrient for the pig but the majority of plant phosphorus is bound in a complex called phytate, which is difficult for the pigs to digest. At least half of the plant phosphorus passes directly through the pig and into the field via the manure.

In order to rectify this, the microbial enzyme phytase is added to the feed. By adding phytase, it is possible to cut down on the addition of extra phosphorus to the feed. There is, however, still room for improvement. As a matter of fact, one-third of the plant phosphorus still passes through the pig.

Closer look at phytate degradation

Scientists from Aarhus University have investigated why addition of the enzyme phytase to pig feed only has a limited effect. Gaining a better understanding of this can make it possible to develop methods that can contribute to an improved degradation of the complex.

"Addition of microbial phytase increases the digestibility of plant phosphorus, including the phytate bound phosphorus, to 60 to 65 per cent. We have wondered why it has not been possible to increase the digestibility even more," according to post-doc, Karoline Blaabjerg, from Aarhus University.

The scientists followed the degradation of phytate-bound phosphorus in the pig stomach. They did this using stomach-fistulated pigs. The pigs had a small opening that could be opened or closed operated into their stomachs. This enabled the scientists to take samples of the stomach contents.

Phosphorus is already absorbed in the first part of the small intestine immediately after it leaves the stomach. This means that the phytate complex with its important phosphorus content must already be broken down in the stomach so that the phosphorus is available for absorption in the intestine.

The scientists took samples from the stomach-fistulated pigs one, two, three and five hours after feeding. They found that the most of the phytate-bound phosphorus passed from the stomach to the intestine during the first hour after feeding at which time, one-fifth of the ingested phytate passed further on to the intestine without being broken down. This means that the phytase is not given enough time to act on a great part of the feed.

"We are therefore working on developing methods that can give phytase more time in which to work. We are also working on paving the way for giving phytase the possibility of a better and quicker access to the phytate," said Ms Blaabjerg.