MICROBIAL-PRODUCTION OF SKATOLE IN THE HIND GUT OF PIGS GIVEN DIFFERENT DIETS AND ITS RELATION TO SKATOLE DEPOSITION IN BACKFAT

The intestinal production of skatole and its deposition in backfat was investigated in 35 uncastrated crossbred male pigs, The pigs were fed five purified non-commercial diets containing either casein or brewer s' yeast slurry as protein source. The yeast slurry diet was used alon e or supplemented with either wheat bran (200 g/kg), sugar-beet pulp ( 200 g/kg), or soya oil (200 g/kg). Skatole concentrations in backfat, and in digesta in different sections of the gastro-intestinal tract we re measured at slaughter (mean weight 112 kg). There were large variat ions in skatole concentrations in the hind gut of different animals gi ven the same diet. Although there was some correlation between skatole in intestinal contents and deposition in adipose tissue, there were a lso large variations between individual animals in their response to i ntestinal skatole. Nevertheless, there was a clear effect of diet on b oth intestinal skatole production and skatole deposition in backfat. T he use of casein as a protein source decreased microbial skatole produ ction, the total amount in the gut, and the concentration in the backf at, Addition of sugar-beet pulp to the yeast slurry diet increased mic robial activity in the intestine (measured as ATP content, concentrati on of short-chain fatty acids, and lowering of digesta pH). There teas a decreased rate of skatole production during in vitro incubations of intestinal content, and less skatole in the hind gut and backfat. In vitro fermentations of freeze-dried ileal effluent inoculated with fae cal bacteria, and addition of substrates to in vitro incubations of in testinal contents, demonstrated that tryptophan availability rather th an microbial activity was the limiting factor for skatole production. The results show that skatole production depends on the amount of prot ein entering the hind gut and the proteolytic activity of the intestin al microbiota. Protein fermentation in the hind gut can be decreased e ither by using move readily digestible protein sources (for example ca sein rather than yeast slurry) which reduce the amount of protein pass ing through to the hind gut, or by adding an alternative energy source which is more readily metabolized by the hind gut microbiota (for exa mple supplementation of the yeast slurry diet with sugar-beet pulp). T his provides a basis for the rational design of diets which will decre ase skatole concentrations in the carcass.