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Low-phytic acid corn to protect water quality?
Dairy Pipeline: August 1998
Katharine F. Knowlton and Joe Herbein
Extension Dairy Scientists, Nutrition
Virginia Tech
540/231-5287, email: knowlton@vt.edu
Much recent attention has been focused on the effect of nitrogen and phosphorus from animal waste on water quality in Virginia and the Chesapeake Bay. Environmental concerns with phosphorous (P) are primarily associated with pollution of surface water. Excess P in water causes algae populations to grow rapidly, or to "bloom." The decomposition of algae consumes dissolved oxygen in the water, and decreases population of fish, clams, crabs, oysters, and other animal life. Phosphorus excretion by all livestock species can be reduced if the availability of P sources in the diet is improved. Recently, seed companies have begun advertising low-phytic acid corn as one way to reduce P excretion by livestock, reducing the potential for impaired water quality. Does this technology have potential for reducing P excretion by dairy cows? Answering this question requires explanation of the impact of phytic acid on P digestion and availability. Most of the P in grains and forages is bound in phytic acid which is not digestible by non-ruminant animals. Corn that has low-phytic acid P has the same total P content as normal corn, but the fraction of that P bound in phytic acid is reduced and the digestible fraction is increased. In poultry and hogs, therefore, the use of low-phytic acid corn is a real source of improvement in P digestion. This improved P digestion allows the P requirement of the animal to be met with a lower P intake, reducing P excretion significantly. An alternative to low-phytic acid grains is use of the enzyme phytase, which degrades phytic acid in grains, releasing P for digestion and absorption. Non-ruminant nutritionists have been evaluating the use of phytase as a feed additive for several years, and have concluded that it is very effective at reducing P excretion by non-ruminants. Rumen bacteria have phytase capability, so P digestion is typically higher in ruminants than in non-ruminants, and we would predict less benefit to low-phytic acid P hybrids in ruminants than in non-ruminants. These low-phytic acid P hybrids have not yet been tested in ruminants, however, although we hope to evaluate them in dairy rations at Virginia Tech in the next year or so. Until research indicates that these hybrids have improved P digestibility in ruminants, we have no reason to either encourage or discourage their use by dairy (or beef) farmers.