Helping pigs to digest phosphorus

Helping pigs to digest phosphorus

Phosphorus is a vital nutrient for pig growth, but pigs do not always digest it well. Research conducted at the University of Illinois has determined how adding various levels of the enzyme phytase to the diet improves how pigs digest the phosphorus in four different feed ingredients. Improving phosphorus digestibility has positive implications for producers' bottom lines as well as for the environment.

The majority of the phosphorus in plant feed ingredients was bound in phytate, said animal sciences professor Hans Stein. It was difficult for pigs to utilise that phosphorus because they could not hydrolyse that phytate molecule. There was an exogenous enzyme called phytase that helped the pigs hydrolyse that phosphorus bond from phytate so the digestibility was increased.

However, there are no data on the response to different levels of phytase in the diet. Stein's team tested the digestibility of phosphorus in conventional corn grain, corn germ, distillers dried grains with solubles (DDGS), and high-protein distillers dried grains (DDG). They tested each ingredient with no phytate and with 500 units, 1,000 units, and 1,500 units of added phytate.

Digestability increase
Supplementation with 500, 1,000, and 1,500 units of phytate increased phosphorus digestibility from 40.9 percent in corn grain with no added phytate to 67.5, 64.5, and 74.9 percent, respectively. Phosphorus digestibility in corn germ increased from 40.7 percent to 59.0, 64.4, and 63.2 percent, respectively. Digestibility of phosphorus in DDGS increased from 76.9 percent to 82.9, 82.5, and 83.0 percent, respectively, but the increase was not significant. Phosphorus digestibility in high protein DDG increased from 77.1 percent to 88.0, 84.1, and 86.9 percent, respectively.

What was discovered was that for corn and corn germ, there was a low digestibility without phytase, but adding phytase to the diet, they increased the digestibility quite dramatically, Stein said.

For DDGS and high-protein DDG, the result was quite different. When adding phytase to DDGS, they did not see a significant increase in digestibility because the digestibility had already been very high. And the same had been true for HP DDG, said Stein. What this tells is that the effect of phytase depends on the particular ingredient.

Non linear response
The second finding was that the response to phytase is not linear. The response to the initial 500 units of phytase was much greater than if they had added another 500 units or another 500 units after that, said Stein. It was a curvilinear response, even for the ingredients where a good response is obtained.

This research will help producers and feed companies to increase the digestibility of phosphorus in ingredients they are already feeding, thus avoiding the expense of adding dicalcium phosphate or monocalcium phosphate to swine diets.

The study was published in a recent issue of the Journal of Animal Science.
Source: University of Illinois


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