If you don’t know the answer, it’s time to find out. Phosphorus is a key mineral and it’s up to you to maintain the proper balance in your pigs’ diets.

Of course there’s also the issue of the environmental consequences of land applying manure containing too much phosphorus. That’s increasingly critical as the movement toward phosphorus-based manure regulations rather than nitrogen-based continues.

The key is to formulate diets for available phosphorus as opposed to total phosphorus. It allows the pig to gain the maximum benefit of phosphorus, while reducing the amount excreted in manure.

There are several nutritional methods to reduce manure phosphorus. These include:

  • Use ingredients that are high in digestible or bioavailable phosphorus, such as distillers dried grains with solubles.
  • Add phytase to the diet.
  • Maintain a 1:1 to 1.5:1 calcium-to-phosphorus ratio when formulating diets.
  • Minimize feed wastage.

To illustrate the point, Jerry Shurson, University of Minnesota animal scientist, conducted three studies evaluating DDGS, phytase, the formulation method used and ratio of calcium to available phosphorus in the diet.

“We looked at how well we were able to meet the pigs’ phosphorus requirements and how much was in the manure,” he notes. “We don’t want to jeopardize the phosphorus for the pig; we want to reduce manure phosphorus output,” says Shurson.

He focused on the nursery-pig phase realizing there’s not a lot of manure produced there. However, a nursery pig excretes more phosphorus per body weight than any other size pig because the phosphorus is more concentrated in the diet.

During the studies, Shurson found that if you put DDGS in the pigs’ diet, you’re able to replace a significant amount of dicalcium supplement. That’s because the fermentation process at an ethanol plant makes the phosphorus more digestible to the pig.

He also points out that phosphorus availability in corn is only 14 percent, which means the pig can’t use 86 percent of it. But with feed that includes DDGS, the pig can use 90 percent of the phosphorus.

In the first study, Shurson found that if you put 10 percent DDGS in the pigs’ diet, you can expect an average reduction in manure phosphorus concentration of 6 percent. If the diet includes 20 percent DDGS, you can expect a 12 percent reduction in the manure. 

The research also shows that when you feed a diet with DDGS, the pig will excrete more manure overall because the dry-matter digestibility declines.

In summary, for every 10 percent DDGS added to the nursery diet, the research shows:

  • Dry matter digestibility decreases.
  • Daily fecal excretion increases by 15 percent.
  • Fecal phosphorus concentration decreases 16 percent.
  • Daily phosphorus excretion decreases from 2 percent to 4 percent.

The study also shows formulating nursery-pig diets on an available-phosphorus basis versus a total-phosphorus basis does the following:

  • Decreases daily total-phosphorus intake by 11 percent.
  • Decreases fecal-phosphorus concentration by 6 percent.
  • May decrease daily fecal excretion by 6 percent.

  In the second study, Shurson compared four diets: a corn/soybean meal diet, a corn/soybean meal diet with phytase, a third with corn/soybean meal and 20 percent DDGS, and the last one with 20 percent DDGS and phytase.

When the researchers added phytase, it reduced the phosphorus excretion in the manure, as well as the total concentration of manure by 33 percent compared to feeding a corn/soybean meal diet without phytase. When researchers added DDGS to the diet, they also found a significant reduction in phosphorus concentration, as well as the total manure excretion. The combination of phytase and 20 percent DDGS reduced phosphorus excretion in manure by 47 percent.

“Adding phytase to the diet can save you more than $1 per ton on feed costs,” says Jim Hedges, vice president of Ralco Nutrition, Marshall, Minn. “Between DDGS and phytase, you can save $3.50 to $4 per ton.”

He also notes that part of the savings involving DDGS is that you can buy it for nearly the same price as corn. In turn, you can save money on dicalcium phosphate as well. (See tables for a breakdown of costs.)

The other piece of the puzzle deals with the amount of calcium-to-available-phosphorus ratio in the pigs’ diet. If the ratio is too wide, calcium will interfere with phosphorus for absorption, which may cause more phosphorus to be excreted in the manure, says Shurson.

In general, he recommends a ratio of two parts calcium to one part available phosphorus so the pig can optimize its use.

“Bottom line DDGS and phytase in combination is a useful, nutritional tool to reduce manure phosphorus concentration and total excretion,” says Shurson.