Most of the phosphorus in plant feed ingredients is bound in phytate, and it is difficult for pigs to utilize that phosphorus because they cannot hydrolyze the phytate molecule. An enzyme called phytase, however, helps pigs hydrolyze that phosphorus bond from phytate so digestibility is increased.
Testing 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. 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.
For corn and corn germ, pigs had a low digestibility without phytase, but as phytase was added to the diet digestibility increased dramatically.
For DDGS and high-protein DDG, the result was quite different. Because these two ingredients have been fermented, some of those phytate bonds are hydrolyzed in the ethanol plant and therefore, less of the phosphorus is bound to phytate in DDGS and high-protein DDG.
When phytase was added to DDGS, there was not a significant increase in digestibility because the digestibility was already very high; the same was true for HP DDG.
The efficacy of phytase appears to depend on the particular ingredient. If it's an ingredient that has a lot of phosphorus bound to phytate, there's a positive response; if it doesn't have much phosphorus bound to phytate, there's not nearly as much response.
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.
Sources: Journal of Animal Science; ACES News
Artwork: Pig in a Stall
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