An in vivo experiment was performed with pigs to study the inhibitory effect of fermented feed on the bacterial population of the gastrointestinal tract. Results demonstrated a significant positive correlation between pH and lactobacilli in the stomach contents of pigs in dry feed as well as in the stomach contents of pigs fed fermented feed. Furthermore, a significant positive correlation between the pH and the numbers of bacteria in the family Enterobacteriaceae in the contents of the stomach of pigs fed dry feed was found. In the stomach contents of pigs fed fermented feed, a significant negative correlation was found between the concentration of the undissociated form of lactic acid and the numbers of Enterobacteriaceae. The numbers of Enterobacteriaceae in the contents of the stomach, ileum, cecum, colon, and rectum of pigs fed fermented feed were significantly lower compared with the contents of the stomach, ileum, caecum, colon, and rectum of pigs fed dry feed. The numbers of total lactobacilli were significantly higher in the stomach contents of pigs fed fermented feed and in the ileum contents of one pig group fed fermented feed compared with the contents of pigs fed dry feed. However, the influence of lactobacilli on numbers of Enterobacteriaceae could not be demonstrated. It was concluded that fermented feed influences the bacterial ecology of the gastrointestinal tract and reduces the levels of Enterobacteriaceae in the different parts of the gastrointestinal tract.Nowadays, there is growing attention on fermented pig feed because it might improve growth performance (8) Fermented feed contains high concentrations of lactic acid, several volatile fatty acids (VFA; acetic acid, butyric acid, and propionic acid), and large numbers of lactobacilli and has a low pH. These four parameters can have, alone or combined, an effect on bacterial ecology of the GIT; lactic acid and VFA are also produced by the indigenous microflora in the GIT (3). Lactic acid and VFA are believed to play a role in reducing the numbers of Enterobacteriaceae, including Salmonella spp. (23,35). Only the undissociated form of lactic acid and VFA can have a bactericidal or bacteriostatic effect (26). The exact concentrations of these undissociated acids and the possible effect on bacterial groups in the content of the stomach and other sites of intestinal tract in pigs fed fermented feed are not known. Fermented feed may reduce the pH in the entire GIT (5, 13, 24), thereby enhancing the effect of VFA on Enterobacteriaceae and probably on Salmonella spp.Another hypothesis for Salmonella reduction is that lactobacilli ingested with fermented feed compete with (potential) pathogenic bacteria in the GIT by strengthening colonization resistance (21). However, the effect of feed-associated lactobacilli on GIT bacterial ecology remains unknown. Very little research has been performed in tracking feed-associated lactobacilli in the GIT of the pig and their possible influence on the bacterial ecology of the GIT. Another mechanism proposed to ...

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To protect consumers from Salmonella infection acquired through the consumption of pork meat, it is necessary to eradicate Salmonella from pork. In order to achieve this, the whole pork production chain should be free from Salmonella, including the pigs at the farm. In epidemiological studies it was concluded that the use of fermented feed plays a signi®cant role in the reduction of Salmonella prevalence in pig farms. However, the mechanism of Salmonella reduction in fermented feed is not known. A controlled feed fermentation was performed using a pure culture of Lactobacillus plantarum. pH reduction, organic acid pro®les and bacterial counts were determined. In L plantarum-fermented feed, lactic acid and acetic acid were produced and the pH dropped to a value below 4.0. Antimicrobial products (bacteriocins) could not be detected. The results showed that the produced lactic and acetic acid and the pH in the feed are responsible for Salmonella reduction in fermented feed. L plantarum did not show any other antimicrobial effect on Salmonella.

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