Effect of Select Tannin Sources on Pathogen Control and Microbial Nitrogen Metabolism in Composted Poultry Litter Intended for Use as a Ruminant Crude Protein Feedstuff

Abstract

Poultry litter is a good crude protein supplement for ruminants but must be treated to kill pathogens before feeding. Composting effectively kills pathogens but risks loss of ammonia due to uric acid degradation. The objectives of this study were to test the ability of tannins to reduce pathogens and preserve uric acid during poultry litter composting. In two experiments, poultry litter was mixed with phosphate buffer and distributed to 50-ml tubes (three tubes/treatment per sample day) amended with 1 ml buffer alone or buffer containing pine bark, quebracho, chestnut, or mimosa tannins. Treatments achieved 0.63% (wt/wt) quebracho, chestnut, or mimosa tannins in experiment 1, or 4.5% pine bark or 9% quebracho, chestnut, or mimosa tannins in experiment 2. Tubes were inoculated with a novobiocin- and nalidixic acid-resistant Salmonella typhimurium, closed with caps, and incubated at successive 3-day increments at 22, 37, and 42°C, respectively. In experiment 1, bacterial counts in contents collected on days 0, 6, and 9 revealed a treatment by day effect (p < 0.03), with the Salmonella challenge being 1.3 log₁₀ CFU/g higher in quebracho-treated composts than in untreated controls after 6 days of composting. After 9 days of composting, Salmonella, wildtype Escherichia coli, and total aerobes in untreated and all tannin-treated composts were decreased by about 2.0 log₁₀ CFU/g compared to day 0 numbers (3.06, 3.75, and 7.77 log₁₀ CFU/g, respectively). Urea and ammonia concentrations tended (p < 0.10) to be increased in chestnut-treated composts compared to controls and concentrations of uric acid, urea, and ammonia were higher (p < 0.05) after 9 days of composting than on day 0. Despite higher tannin application in experiment 2, antibacterial effects of treatment or day of composting were not observed (p > 0.05). However, treatment by time of composting interactions was observed (p < 0.05), with quebracho- and chestnut-treated composts accumulating more uric acid after 24 h and 9 days of composting and chestnut-, mimosa- or quebracho-treated composts accumulating less ammonia than untreated composts. Results demonstrate that composting may effectively control pathogens and that tannin treatment can help preserve the crude protein quality of composting poultry litter.

Keywords: Escherichia coli; Salmonella; nitrogen metabolism; poultry litter; tannins.

Figure 1

Interaction (p = 0.0156) between treatment and day of composting on the challenge Salmonella typhimurium during 9-days simulated composting of poultry litter treated without (open circles) or with (0.63%) pine bark- (closed squares), quebracho- (closed triangles), chestnut- (closed diamonds), or mimosa- (X) tannins (Experiment 1). Means with unlike uppercase letters differ based on an LSD all pairwise test at p < 0.05. Error bars denote standard deviations from n = 3 independent replicates at each time point.

Figure 2

Denaturing gradient gel electrophoresis dendrogram showing effects of 0.63% tannin treatment on microbial diversity (Experiment 1).

Figure 3

Interactions (p = 0.0001, <0.0001, and <0.0001, respectively) between treatment and time of composting on counts of the challenge Salmonella typhimurium (A), wildtype E. coli (B) and total culturable aerobes (C) during 9-days simulated composting without (open circles) or with 4.5% pine bark (closed squares) or 9% quebracho (closed triangles), chestnut (closed diamonds) or mimosa (X) tannins (Experiment 2). Means with unlike uppercase letters differ based on an LSD all pairwise comparison test at p < 0.05. Error bars denote standard deviations from n = 3 independent replicates at each time point.

Figure 4

Interactions (p = 0.0007, 02211, and <0.0001, respectively) between treatment and time of composting on concentrations of uric acid (A), urea, (B) and ammonia (C) during 9-days simulated composting without (open circles) or with 4.5% pine bark (closed squares) or 9% quebracho (closed triangles), chestnut (closed diamonds), or mimosa (X) tannins (Experiment 2). Means with unlike uppercase letters differ based on an LSD all pairwise comparison test at p < 0.05. Error bars denote standard deviations from n = 3 independent replicates at each time point.