University of Kentucky (UK) animal scientists tested new, low-phytic acid corn varieties for feeding pigs and chicks. The researchers found more phosphorus was available for absorption and use by pigs when they ate the low-phytate corn variety as compared to normal corn.
"One of the most exciting discoveries to surface in corn breeding in recent years is the discovery of low phytic acid (low phytate) genes," says Gary Cromwell, UK swine nutritionist. Low-phytate genes were first discovered by Victor Raboy, a USDA plant breeder at Montana State University. These mutant genes block the synthesis of phytic acid in corn kernels as they are produced on the ear without affecting the amount of total phosphorus. As a result, the inorganic phosphorus content of corn is markedly increased. One of the major seed companies, Pioneer Hi-Bred International, has put the low-phytate gene into some of its hybrid corn lines.
"What makes this discovery so exciting is the tremendous potential that this corn has for reducing environmental pollution from high-phosphorus pig and poultry manure," Cromwell relates.
Most (60-80%) of the phosphorus in corn is in a complex form called phytic acid (or phytate). Pigs and poultry do not have the digestive enzyme (phytase) in their gastrointestinal tract to break down thephytate. This means most of the phosphorus in corn and soybean meal passes through the tract unused, and is excreted in the manure. The excreted phosphorus can potentially contribute to environmental pollution if high-phosphorus manure is applied to cropland and the excess phosphorus finds its way into surface waters.
Low-phytate corn has about half as much phytate phosphorus as normal corn (Table 6). And better yet, this mutant corn has about two to three times more highly digestible inorganic phosphorus than normal corn (Table 6).
The UK researchers worked with Optimum Quality Grains, L.L.C., a joint venture involving Pioneer Hi-Bred International and Dupont, in testing the new type of corn. The researchers found in studies with pigs and chicks that the phosphorus in low-phytate corn was about three to four times more bioavailable than the phosphorus in normal corn. "Specifically, we found in pig studies that this gene increased the bioavailability of phosphorus from approximately 20% in normal corn up to 75% in low-phytate corn," Cromwell says.
This finding is significant because it means when low-phytate corn is fed, less supplemental phosphorus is needed to meet the animal's dietary phosphorus requirements. Results of feeding tests conducted at UK with both growing pigs (Table 7) and finishing pigs (Table 8) indicate that feeding pigs low-phytate corn-soybean meal diets with 0.1% less total phosphorus than normal, results in similar performance and bone mineralization as in pigs fed normal corn-soybean meal diets.
"More importantly, phosphorus excretion is markedly reduced when low-phytate corn is fed," Cromwell says. "In a recent experiment, we found that pigs fed low-phytate corn-soybean meal diets containing 0.1% less total phosphorus than normal corn-soy diets excreted one-third less phosphorus in their manure."
Even with the feeding of low-phytate corn, there is still quite a bit of unusable phytate phosphorus in diets that originate from soybean meal. Experiments are presently underway at UK to assess the effects of adding a microbial phytase supplement to corn-soybean meal diets containing either normal corn or low-phytate corn. Also, low-phytate soybeans are on the horizon. All of these new technologies-supplemental phytase, low- phytate corn and low-phytate soybeans-have tremendous potential as a means of reducing the problems of phosphorus excretion in pork production systems.
Preliminary testing by Optimum Quality Grains, L.L.C, indicates that low- phytate corn produces yields that are comparable to normal corn. The protein, lysine, starch and other important nutritional traits are not affected by the low- phytate gene. The gene apparently only affects the type of phosphorus in the corn grain.
A side benefit of the reduced phytic acid (which is a strong chelating agent) is that binding of zinc and other trace minerals is less likely to occur in the intestinal tract when this type of corn is fed. Thus, dietary levels of some trace elements such as zinc can also be reduced, which will also reduce excretion of these trace elements.
Optimum Quality Grains estimates seed will be commercially available for planting in the spring of 2000.
Researchers: Gary L. Cromwell and James L. Pierce, University of Kentucky. Phone Cromwell at (606) 257-7534, or email gcromwel@ca.uky.edu.