Ash from combusted hog manure and incinerated carcasses is being tested as mineral sources for use in swine rations.

The ash from fecal material is a byproduct of gasification that produces combustible gasses or electricity. Another possibility is the ash from dead animal carcasses incinerated on farms. Both processes destroy bacteria.

Feeding tests with growing pigs at North Carolina State University show that the ash from manure is a good source of essential minerals.

“The ash contained high levels of calcium, 11.5 percent; and phosphorus, 13.3 percent,” explains Theo van Kempen, animal scientist. In addition, it contained important micro-minerals, including 0.18 percent zinc, 0.15 percent copper and 0.73 percent iron.

Also present was a high concentration of potassium, 12 percent, which van Kempen says should be watched when formulating rations, and magnesium at 5.8 percent. “But recent research with magnesium shows that higher levels in swine diets may benefit meat quality.”

Four minerals, which are excreted in urine, were notably low, says van Kempen: Sodium, chloride, sulfur and nitrogen. Any of the last three are lost in the flue gas during combustion.

In his feeding tests with growing pigs, digestibility of the ash was close to that of commercial mineral sources.

“Our work so far, shows that ash is an excellent source of minerals for pigs and suggests it may be the ultimate method of recycling minerals,” adds van Kempen.

He notes that one important question does remain: Will the magnesium level in ash cause an excess of it in the animal’s manure making recycling impractical? “If so,” he says, “the answer may be to process the ash to extract beneficial minerals.”

Additional feeding tests are under way, including ones using ash from incinerated carcasses from hogs that died. “If results are as encouraging as those from feeding combusted feces,” says van Kempen, “recycling in feed solves environmental problems while reducing the need for supplemental and often expensive minerals.”