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Previous studies have indicated that reducing dietary CP may improve N utilization and effectively diminish manure ammonia emissions. However, the response of manure odor emissions to such dietary modifications has been inconsistent. Previous research has demonstrated a decrease in odor emissions in response to consumption of fermentable carbohydrate, and this has been partially attributed to promoting lactic acid bacteria. Therefore, the objective of the current experiment was to induce decreased lactobacilli (DL) numbers in the distal gastrointestinal tract (dGIT; cecum + colon) of finishing pigs offered both high- and low-CP diets through consumption of chitosan, and examine the influence of this model on manure ammonia and odor emissions when compared with a positive control diet. A 2 x 2 factorial arrangement of treatments was conducted to investigate the effect of including chitosan [0 (positive control) vs. 20 g/kg of feed] and high or low dietary CP concentration (200 vs. 150 g/kg of feed) on nutrient digestibility, N utilization, selected bacterial populations, and metabolite composition of the dGIT and manure emissions from finisher pigs (60.3 kg).
Consumption of chitosan had no influence (P < 0.05) on nutrient digestibility or N utilization. In both high- and low- CP diets, consumption of chitosan decreased the lactobacilli-to-Enterobacteriaceae ratio (P < 0.01), generating an DL population, and increased pH (P < 0.01) in the dGIT and ammonia (P = 0.02) in the cecum compared with diets that supported normal lactobacilli populations. Consumption of chitosan decreased molar proportions of butyric acid (P < 0.01) and increased valeric acid (P < 0.01) in the dGIT compared with unsupplemented diets. Furthermore, consumption of chitosan increased manure odor emissions (P = 0.05) compared with unsupplemented diets. There was no effect (P > 0.05) of chitosan consumption on manure ammonia emissions from 0 to 240 h. The current study demonstrated that dietary chitosan suppressed populations of lactobacilli in the dGIT. In response, a considerable increase in Enterobacteriaceae, markers of protein fermentation, and manure odor emissions was observed compared with the positive control diet. These effects were observed in pigs offered both high-and low-CP diets.
The current study indicates a possible role for lactic-acid bacteria in modulating manure odor emissions relatively independent of the proportions of dietary CP available for fermentation in the dGIT.
CJ O'Shea, T Sweeney, MB Lynch, JJ Callan and JV O'Doherty, 2011. Modification of selected bacteria and markers of protein fermentation in the distal gastrointestinal tract of pigs upon consumption of chitosan is accompanied by heightened manure odor emissions. Journal of Animal Science, 89: 1366-1375. http://dx.doi.org/10.2527/jas.2010-2922