Effect of Feed Ingredients on the Antifungal Activity of Propionic Acid ,

The effect of mixing varying amounts of soybean meal, fish meal, poultry by-product meal, corn gluten meal, fat, and limestone in corn meal on the antifungal activity of propionic acid was assessed by measuring the production of CO2 by fungi in the mixtures. Antagonism was observed with soybean meal, fish meal, poultry by-product meal, and limestone. Corn gluten meal was without effect while the addition of fat to corn meal enhanced the activity of propionic acid. The antagonistic effects can be rationalized on the basis of the free acid form of propionic acid being converted to the less active salt form by the buffering capacity of the antagonistic supplements. The lack of an effect with corn gluten meal would reside in its low buffering capacity and the synergistic effect of fat can be explained on the basis of enhanced distribution of propionic acid. That the activity of antifungal agents can be controlled by feed ingredients may be useful in establishing usage levels.