Impact of dietary protein on microbiota composition and activity in the gastrointestinal tract of piglets in relation to gut health: a review

Abstract

In pigs, the microbial ecosystem of the gastrointestinal tract (GIT) is influenced by various factors; however, variations in diet composition have been identified as one of the most important determinants. Marked changes in fermentation activities and microbial ecology may occur when altering the diet, for example, from milk to solid feed during weaning. In that way, access of pathogens to the disturbed ecosystem is alleviated, leading to infectious diseases and diarrhea. Thus, there is increasing interest in improving intestinal health by use of dietary ingredients suitable to beneficially affect the microbial composition and activity. For example, fermentable carbohydrates have been shown to promote growth of beneficial Lactobacillus species and bifidobacteria, thereby enhancing colonization resistance against potential pathogens or production of short-chain fatty acids, which can be used as energy source for epithelial cells. On the other hand, fermentation of protein results in the production of various potentially toxic products, such as amines and NH3, and is often associated with growth of potential pathogens. In that way, excessive protein intake has been shown to stimulate the growth of potentially pathogenic species such as Clostridium perfringens, and to reduce fecal counts of beneficial bifidobacteria. Therefore, it seems to be a promising approach to support growth and metabolic activity of the beneficial microbiota by developing suitable feeding strategies. For example, a reduction of dietary CP content and, at the same time, dietary supplementation with fermentable carbohydrates have proven to successfully suppress protein fermentation. In addition, the intestinal microbiota seems to be sensible to variations in dietary protein source, such as the use of highly digestible protein sources may reduce growth of protein-fermenting and potentially pathogenic species. The objective of the present review is to assess the impact of dietary protein on microbiota composition and activity in the GIT of piglets. Attention will be given to studies designed to determine the effect of variations in total protein supply, protein source and supplementation of fermentable carbohydrates to the diet on composition and metabolic activity of the intestinal microbiota.

Down-regulation of monocarboxylate transporter 1 (MCT1) gene expression in the colon of piglets is linked to bacterial protein fermentation and pro-inflammatory cytokine-mediated signalling

“…Colonic tissue from pigs fed commercial standard diets was mounted on Ussing chambers and mucosally exposed to different metabolites. Changes in short-circuit current were found to be higher (P,0·05) after the mucosal addition of NH 4 Cl compared with control chambers and chambers treated with Na-butyrate and TNF-a, where practically no biologically relevant change occurred (data not shown). The expression of MCT1, IL-8, TNF-a and IFN-g was subsequently analysed.…”

“…The expression of MCT1, IL-8, TNF-a and IFN-g was subsequently analysed. MCT1 gene expression was higher (P,0·05) after Na-butyrate treatment and lower (P,0·05) after exposure to NH 4 Cl and TNF-a compared with the untreated controls ( Fig. 1(A)).…”

“…After equilibration for approximately 15 -30 min, tissues were short-circuited by clamping the voltage at 0 mV. The test substrates Na-butyrate and NH 4 Cl were added to the mucosal and TNF-a to the serosal side of the tissue to give a final concentration of 20 mmol/l, 20 mmol/l and 50 ng/ml, respectively, with osmolality adjusted to 295 (SE 10) mOsmol/l. After 1 h of incubation, the exposed portion of the tissue was harvested and immediately stored in RNAlater RNA Stabilization Reagent (Qiagen GmbH) at 2 808C until use.…”

“…To study the influence of different concentrations of Nabutyrate, NH 4 Cl and TNF-a on the expression of MCT1 and cytokines, in vitro cell-culture experiments using Caco-2 cells were performed. Caco-2 cells were grown routinely in a T-75 plastic flask at 378C in an atmosphere of 5 % CO 2 , and maintained in Eagle's minimum essential medium (LGC Standards) supplemented with 20 % fetal bovine serum, 100 units penicillin/ml and 100 mg streptomycin/ml (Biochrom).…”

“…For example, protein level and quality in pig diets have been shown to be related to diarrhoea and shedding of enterotoxigenic Escherichia coli after a challenge (5,6) . A promising approach to reduce the formation of harmful metabolites from protein fermentation in the large intestine is the inclusion of fermentable carbohydrates in the diet (4,7,8) . This approach can be used to direct bacterial fermentation activity towards utilisation of carbohydrates instead of proteins, yielding lower luminal concentrations of branched-chain fatty acids and NH 3 and higher levels of SCFA.…”