the influence of lentinus edodes (shiitake mushroom) preparations on bacteriological and morphological aspects of the small intestine in piglets

Abstract

Among substances intended to replace growth promoting antibiotics in pig nutrition, non-digestible oligosaccharides or polysaccharides could be potential alternative compounds. Therefore, the influence of β-1,3-1,6 glucans on bacteriological, biochemical and morphological aspects of the small intestine in weaned piglets was investigated. As sources of β-glucans, Lentinan (extract of Lentinus edodes mycelium) or dried L. edodes mycelium were added to the diet. Four homogenous groups of 5 newly weaned piglets (4 weeks of age) received one of four diets: control diet (C), C supplemented with Avilamycin (50 mg/kg, positive control), C supplemented with 0.1% of Lentinan and C supplemented with 5% of dried L. edodes mycelium powder. A first group of 10 piglets was euthanized after 11 days and the remaining 10 on day 12 of the experiment. The gastrointestinal tract was divided in segments and samples taken from digesta (stomach, proximal and distal jejunum, caecum), mucosal scrapings (jejunum) and ring shaped tissue samples (1 cm) of proximal and distal jejunum. Bacterial counts were made with digesta and mucosal samples, and short-chain fatty acids (SCFA), lactic acid and ammonia concentrations were determined. Tissue samples of both jejunal sites were embedded in paraffin wax for morphometrical (villus length, crypt depth) and histological observations (numbers of intraepithelial lymphocytes (IEL), goblet cells, apoptotic enterocytes on villi, mitotic cells in crypts). Only the diet containing 5% of dried L. edodes consistently resulted in lower viable counts (ca. 1 – 2 log₁₀ CFU) of total bacteria, E. coli, streptococci and lactic acid bacteria, and luminal and mucosal effects agreed very well. With this diet, acetate and butyrate concentrations in the distal jejunum were doubled, which is favourable in view of the trophic effect on enterocytes and colonocytes. Villus length (V) was increased with both diets containing β-glucans while crypt depth (C) was not altered, but V/C was higher. IEL counts were decreased by both diets although bacterial numbers, which is only one parameter of bacterial load, were only diminished with the L. edodes feed. The three supplemented feeds lowered the number of apoptotic enterocytes on the villi, but these numbers were very low (control diet : 44 cells per 100 villi), making clear interpretation difficult. The mitotic index was slightly lower with the L. edodes feed, although not statistically significant. Decreased viable counts observed with the latter diet is a favourable effect as it is accepted that a lower bacterial load causes lower turnover rates of the intestinal epithelial cells, while there is also less competition for specific substrates. A higher V/C ratio, a smaller number of IEL in the epithelium and a lower apoptotic index also indicate slower turnover rate of the mucosa when Lentinan and L. edodes diets were fed. The inconsistent effects observed with Lentinan were probably due to the low amount added to the diet. It should be taken into account that the influence of L. edodes mycelium powder was more likely due to the presence of antibacterial compounds (eg. lenthionine, lentinamycin, terpenoids, polyphenols), rather than to an immunostimulating action of β-glucans with increased release of IgA onto the mucosa surface.

Keywords:

• Piglets
• Oligosaccharides
• Beta-glucans
• Lentinus edodes
• Intestinal microorganisms
• Intestine
• Morphology

Acknowledgements

The research was supported with grants from the former Federal Ministry of Agriculture, DG6, Brussels and VITAMEX N.V., Drongen, Belgium. C. Vermander, A. Ovijn, A. Maes, A. Turtelboom, D. Bayens and S. Coolsaet are thanked for skillful technical assistance. We are also grateful to Prof. H. Lauwers, Prof. R. Ducatelle, Prof. C. Cuvelier, Dr. De Metter, Ghent University, Belgium and Prof. T. Sakata, Ishinomaki Senshu University, Ishinomaki, Japan, for their advice.

Notes

¹This work was accepted and presented as a poster at the 3rd Joint RRI-INRA 2002 symposium organized by INRA, Theix, (France) and The Rowett Research Institute, Aberdeen (UK) from June 12 – 15 held in Aberdeen.

Additional information

Notes on contributors

K Molly

1This work was accepted and presented as a poster at the 3rd Joint RRI-INRA 2002 symposium organized by INRA, Theix, (France) and The Rowett Research Institute, Aberdeen (UK) from June 12 – 15 held in Aberdeen.