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The intention of this study was to test both in vitro and in vivo whether feed additives have an inhibitory effect on E. coli infection of piglets.
The intestinal porcine epithelial cell line IPEC-J2 was used as in vitro model to assess effects of feed additives on adhesion of a F4 positive E. coli strain (ETEC). Feed additives were dissolved in cell medium, which was then used to grow cells in different feed additive concentrations. Cells were infected with a bacterial suspension previously stained with the fluorescent dye 5,6-carboxymethyl fluorescein diacetate succinimidyl ester. Bacterial adhesion was characterized by fluorescence intensity measured by flow cytometry of the IPEC-J2 cells.
A piglet feeding trial was performed in which 81 piglets were challenged with ETEC twice 72 and 76 hours after weaning. Piglets were fed a complete diet that met nutritional requirements and contained the feed additive in the concentration recommended by the producer. Health and performance of piglets were thoroughly examined during the whole course of the experiment (21 days). The objective of the challenge trial was to establish a suitable model for experimental infection (1010 cfu / animal) of weaner piglets (3 weeks old) using an ETEC strain positive for F4 fimbriae and both heat labile (LT1) and heat stabile (St1p and St2) toxins.
The in vitro trials showed that the yeast fermentation product has the potential to inhibit ETEC adhesion to IPEC-J2 cells. The relative fluorescence intensity of infected cells was reduced by 47.3 and 43.5% in the 10-² and 10-3 % dilutions, the number of infected cells decreased by 94.7 and 80.4%, respectively.
The challenge trial resulted in marked clinical signs in all infected piglets and an overall loss of 16%. A marked decrease in fecal dry matter was observed in 83% of infected piglets.
Shedding of ETEC virulence factor genes fae and est-II was observed in 92.9% of the examined animals in high amounts. The tested feed additives were unable to protect piglets after ETEC challenge. However, the feed additives Acid Mix and Thyme were able to produce results similar to those of the non-infected control group in feed intake and body weight.
Given the present data an influence of the investigated feed additives on intestinal physiology appears probable. However, to assess specific antibacterial potential further studies are required. Factors that potentially have a negative influence on effectiveness of feed additives (inclusion rate/dose in diet, effect of stomach pH, interactions with other feed components) should thereby be given particular attention.