Disease outbreaks are recognized as a major bottleneck for aquaculture production and trade. It is estimated that annual losses due to pathogenic diseases can reach deficits of billions of dollars to global aquaculture. Aggravating this scenario , the increased demand for alternative protein ingredients to replace fishmeal in aquafeeds has led to higher inclusion of plant feedstuffs, and these ingredients may contain anti-nutritional factors and secondary metabolites that can impair the functional competency of the gastrointestinal tract (GIT) against pathogen translocation. Organic acids or acidifiers are promising feed additives that can alleviate these issues by inhibiting the proliferation of pathogenic bacteria in the intestine. They are composed of short- and medium-chain fatty acids with bacteriostatic properties resulting from fermentation of complex carbohydrates by autochthonous bacteria. Their relatively small chemical structures are lipophilic and can diffuse across the cell membrane of gram-negative bacteria, and within the bacterial cytosol, the dissociation of the se molecules acidify the intracellular environment, ultimately leading to ATP exhaustion of the bacteria which inhibits cellular growth and induces death .
The objective of this study was to investigate in vitro and in vivo the supplementation of two organic acids individually as well as in combination in a high-plant-protein diet with the carnivorous red drum . A basal diet was formulated with soybean products to provide 75% of the total crude protein , and supplemented with either 0 or 0.5 g kg-1 of butyrate, propionate, or their combination. In the in vitro experiment, digesta was aseptically collected from 16 juvenile fish and incubated under anaerobic conditions with an incomplete anaerobic media supplemented with the experimental diets. After 24 h incubation at 27°C, the samples were frozen and further processed for DNA extraction and the microbial communities were compared among treatments by denaturing gradient gel electrophoresis (DGGE). Results from this trial suggested that the supplementation of the organic acids mildly affected the bacterial community, having a 90% similarity with that of the basal diet. A 60- day feeding trial also was conducted to evaluate if the experimental diets would affect production parameters and intestinal microbial community. Performance of the fish was analyzed as a mixed model, having a 2×2 factorial design (absence or presence of butyrate or propionate as main factors) and the disposition of the aquaria serving as a covariant. Digesta contents were collected at day 30 and 60 of feeding to compare the microbial communities within treatments by DGGE . The supplementation of propionate to the diet slightly but significantly (P=0.02) impaired the growth performance of red drum, and feed efficiency was also slightly but significantly (P=0.01) impaired by the addition of butyrate. The DGGE results showed that the bacterial microbiome of the gut was significantly affected by the supplementation of the organic acids individually and by their combination, when compared to fish fed the basal diet at the two different collection points. Supplementing organic acids in high-plant-protein ingredients did not benefit the growth performance of red drum. Further investigation of the immunological parameters of fish plasma and results for the intestinal DNA for Next Generation Sequencing are pending.
CNPQ: 207141/2014-2