Effect of Pelleting of Poultry Feed on the Activity of Molds and Mold Inhibitors

Paired samples of mash and pellets made from the mash were taken at feed mills and compared for their mold count and fungal activity as measured by metabolic CO2 production. Four paired samples contained Mold-X, a commercial mold inhibitor, of which the major active ingredient is propionic acid, and four paired samples did not contain a mold inhibitor. Pelleting reduced the mold counts by a factor of about 100 to 10,000, depending upon the sample. Incubation of the samples at 29 C after adjusting the water content to 20, 25, or 30% caused an approximate doubling of the time required for onset of metabolic CO2 production by the pelleted feed as compared to the mash. Incorporation of the mold inhibitor into mash appeared to give a similar lag in onset of CO2 production. Pellets made from mash containing the mold inhibitor had an additional doubling in the delay of onset of CO2 production. In a model system composed of corn meal to which graded doses of propionic acid were added, the concentration of inhibitor that provided 50% inhibition was found to increase with time of incubation. The lag in onset of CO2 production in this system was found to be 1 or 2 days depending on whether the corn meal was heated for 5 min at 60 or 70 to 85 C, respectively. Heat and propionic acid also interacted to reduce the mold count of corn meal in the model system. It would appear that the effectiveness of propionic acid as a mold inhibitor can -be greatly increased by the pelleting process and that a decrease in the fungal burden of feed is an attribute of pelleting.