A LABORATORY EVALUATION OF ORGANIC ACIDS AND FORMALDEHYDE AS PRESERVATIVES FOR WET CAGE LAYER EXCRETA INTENDED FOR RECYCLING BY FEEDING TO LIVESTOCK

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Abstract
A previous study on the feeding value of wet cage layer excreta (CLE) indicated the need for a chemical preservative to stabilize CLE and control odor. An acetic–propionic acid mixture, formaldehyde, and an acetic–propionic acid-formaldehyde mixture were evaluated as preservatives during a 28-day storage period. Two-kilogram amounts of 3-day-old CLE were treated with the three chemicals each at 0.25% (low rate), 0.50% (medium rate) and 1.0% (high rate) wt/wt. Each excreta sample was inoculated with 5 × 106Salmonella infantis/g. All treatments were replicated twice and stored uncovered at 22 °C. Discoloration, mold growth and putrefaction as well as changes in pH, dry matter, total nitrogen, ammoniacal nitrogen and volatile fatty acid content of samples taken at 0, 7, 14 and 28 days after treatment were the criteria of evaluation. Total Coliform count and Salmonella recovery were also recorded. The acetic–propionic acid mixture appeared most effective in retarding physical deterioration, especially mold growth and discoloration. All three chemicals were equally effective (P >.05) in reducing nitrogen losses. A level × time interaction effect (P <.05) was obtained for all parameters. Compared to the control, the medium and high rates of treatment effectively retarded deterioration for 7 and 14 days, respectively. The rise in pH, nitrogen losses, ammoniacal nitrogen and butyric acid content of samples treated at the medium and high rates were lower (P <.05) than for the control, and spoilage was less extensive. Beyond 14 days, spoilage and nitrogen losses were similar (P >.05) to that observed in the control. The low treatment rate was in general ineffective in preventing spoilage and nitrogen losses. Total Coliform counts decreased with time, and Salmonellae recovery was nil from 7 days post-inoculation for all treatments including the control.

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