Efficiency of digestion in germ-free and conventional rabbits

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Abstract
1. Germ-free (GF) and conventional (CV) rabbits wearing collars to prevent coprophagy were fed an autoclaved diet with added cellulose. Their faecal excretion was analysed to determine nutrient digestibility.2. Clearly distinguishable hard faeces were excreted by the GF rabbit only if the diet contained at least 15% cellulose. Unlike CV rabbits, the GF rabbits did not consume their soft faeces even when permitted to do so. Soft faeces made up a larger proportion of the total output of GF than of CV rabbits. Food intake and total dry-matter excretion per kg body-weight were similar in both groups.3. Although digestibility of dry matter was similar in the two groups, in the GF rabbits there was a higher digestibility of crude fat and true protein and a lower digestibility of crude fibre and nitrogen-free extract. GF rabbits excreted a higher percentage of ingested calcium and phosphorus in the urine than did CV rabbits.4. The results suggest that intestinal microbes, even without the enhancing effect of coprophagy, aid in the digestion of carbohydrate by rabbits. The greater faecal excretion of crude fat and true protein by CV rabbits could result from poorer digestion and absorption, but could also represent nutrients synthesized by microbes from simpler materials. The reingestion of faecal crude fat and true protein might therefore improve the quality of the total nutrient intake. The results suggest ways of assuring an adequate dietary intake by GF rabbits in the absence of contributions from an intestinal microflora.