Researchers at the University of Kentucky have found that feeding a genetically enhanced corn can help reduce the amount of phosphorus excreted in hog manure.

Low-phytate corn has the same amount of phosphorus but less phytate phosphorus (0.10% vs. 0.20%) and more inorganic phosphorus (0.18% vs. 0.05%) than normal corn.

Pigs are unable to utilize phosphorus in its most common form (phytate) because their digestive tract lacks phytase, an enzyme needed to separate the phosphate groups from the phytate molecule.

As a result, pig diets must be supplemented with a highly available inorganic phosphorus source, such as dicalcium phosphate. Because of the poor utilization of phytate and large amounts of supplemental inorganic phosphorus in diets, pigs excrete large amounts of phosphorus in their manure, and this contributes to environmental concerns.

Researchers found that the bioavailability of the phosphorus in low-phytate corn is considerably higher than in normal corn. Pigs utilize only about 10-20% of the phosphorus in conventional corn, but they can utilize about 75% of the phosphorus in low-phytate corn.

This means that the phosphorus level in pig diets can be lowered by 0.1 of a percentage point when low-phytate corn is fed to pigs. That is equal to an 11-lb. reduction in dicalcium phosphate per ton of feed.

Table 1 shows that this type of dietary modification results in optimal pig performance and bone strength, and a 38% reduction in the amount of phosphorus excreted by growing-finishing pigs.

Table 2 shows the results of another experiment with finishing pigs in which feeding low-phytate corn reduced phosphorus excretion by 43%.

Another means of increasing the utilization of the phosphorus in corn and soybean meal is to add phytase enzyme to the diet.

In a third experiment, phytase was found to improve performance and bone strength when either type of corn was included in corn-soy diets. However, the responses to added phytase were more pronounced in diets containing normal corn as compared with those containing low-phytate corn.

The addition of phytase to a diet supplemented with monosodium phosphate, a highly available source of phosphorus, failed to improve bone strength.

In a fourth study, phytase supplementation of normal corn-soy diets resulted in a 23% reduction in phosphorus excretion compared with feeding a conventional normal corn-soy diet.

Feeding low-phytate corn instead of normal corn resulted in a 35% reduction in phosphorus excretion. The combined effects of adding supplemental phytase to the diet and feeding low-phytate corn resulted in pigs excreting more than 50% less phosphorus in their manure.

Researchers: Gary Cromwell, James Pierce and Merlin Lindemann, University of Kentucky. Phone Cromwell at (606) 257-7534 or e-mail gcromwel@ca.uky.edu.