News from the Midwest Sectional Meetings, March 16-18, 1998, Des Moines, Iowa
Contacts:
Gary Allee (573) 882-7726
Joel Spencer (573) 882-7726
Low-phytate-corn rations reduce phosphorus excreted by swine in Missouri feeding trials
COLUMBIA, Mo. – Hogs fed low-phytate corn, a genetically modified corn naturally high in digestible phosphorus, excrete less phosphorus in manure. This could reduce the potential for pollution from hog farms, according to animal scientists at the University of Missouri-Columbia.
"There is a tremendous increase in digestibility of phosphorus in the low-phytate corn," said Gary Allee, MU swine nutritionist. Allee and Joel Spencer, MU graduate student, reported the first swine feeding trials with the new corn at the Midwest meeting of the American Society of Animal Science in Des Moines, Iowa.
Analysis of waste from pigs fed low-phytate corn showed an average 37 percent reduction in phosphorus.
No adverse effects from feeding low-phytate corn were seen. In feeding trials with growing pigs, 64 percent of the phosphorus in low-phytate corn was available. That compares with 10 percent available from a genetically similar corn with normal phytate levels.
When MU scientists ran laboratory tests on the two corns they found phosphorous availability similar to that in feeding trails. Low-phytate corn had 57 percent of its phosphorus in a bioavailable form, while normal corn had only 11 percent available.
"Low-phytate corn comes very close to supplying all phosphorus needs of a finishing pig," Allee said. Traditionally, phosphorus is added to swine rations to ensure bone and muscle development for rapid growth.
In current corn hybrids, much of the naturally occurring phosphorus in the kernel is tied up as phytate, which is poorly digested by swine. As a result, phosphorus locked in phytate is excreted in manure. To offset the unavailable phosphorus, swine producers add digestible phosphorus to a swine diet. This causes even more phosphorus to be excreted.
Spreading hog manure high in phosphorus on farmland can lead to a build up in the soil. While phosphorous is an essential nutrient for growing crops, an excess applied to the land can become a pollutant. That excess phosphorus can be carried from the field in runoff, leading to pollution in streams and rivers.
Corn used in the MU feeding trials came from a hybrid genetically altered with a naturally occurring mutant by Victor Raboy with the USDA Agricultural Research Service at Aberdeen, Idaho. Also cooperating were Tom Sauber and David Ertle, researchers at Pioneer Hi-Bred International, Johnston, Iowa. The company, which is developing the corn for commercial release, provided the corn for the feeding trials from plots in central Iowa.
"We received half of the low-phytate corn crop from 1996 for the swine feeding trials in Missouri," Allee said. More corn is available for further trials this year.
In MU finishing trials, 210 barrows from a line of high-lean pigs were divided into groups receiving normal corn and low-phytate corn. Another variable compared supplementation with dicalcium phosphate and with no added phosphorus. Pigs fed the low-phytate ration grew larger loin-eye muscles. "This suggests that amino acid (protein) availability is higher in the low-phytate corn," Allee said.
Pigs on low-phytate corn had similar average daily gain to pigs fed normal corn and supplemental phosphorus, but feed efficiency was slightly better in the pigs on the low-phytate corn.
Allee said that phytate not only ties up phosphorus, but also "grabs and holds" other essential elements in a ration, such as calcium and zinc.
Pigs fed normal corn with no supplemental phosphorus showed all the clinical signs of phosphorus deficiency, Allee said. "They had trouble walking. And, when we checked the carcasses at the slaughter plant, we saw broken ribs and even broken spines.
"We saw no cracked or broken bones on animals fed low-phytate corn alone."
Allee said he is not willing, yet, to say that no supplemental phosphorus will be needed in swine finishing rations made from low-phytate corn. "We were feeding barrows with high daily feed intake."
But Allee added, "Low-phytate corn can be fed to grower-finisher swine with no detrimental effects on performance or carcass traits."
Low-phytate corn is just the first step in asking geneticists to design grain specifically for a ration, Allee said. "We just haven't told plant breeders what we need."
The research was funded by Pioneer Hi-Bred International, Inc., and the MU Agricultural Experiment Station as part of a six-state consortium of land-grant universities studying ways to reduce pollution on swine farms.
Pioneer has announced that low-phytate seed corn will be available in two years.
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