Organic acids in diets for entire male pigs: Effect on skatole level, microbiota in digesta, and growth performance
Introduction
Concerns about animal welfare have led to restrictions on castration practices of male pigs in Norway and other European countries. A major problem with meat from entire male pigs is boar taint. Skatole (3-methylindole), a main compound leading to boar taint, is produced in the hind-gut of pigs by specialized bacteria (Yokoyama et al., 1977). l-tryptophan originating from the gut mucosa cell debris from the distal part of the gastrointestinal tract is the major precursor for microbial skatole formation (Yokoyama and Carlson, 1979, Claus et al., 1994). Skatole production in the hind-gut of pigs has been shown to be affected by several dietary factors. Addition of high levels of carbohydrates with low ileal digestibility such as chicory inulin (Rideout et al., 2004, Lanthier et al., 2006) or raw potato starch (Claus et al., 2003, Andersson et al., 2005, Lösel and Claus, 2005), which favors butyrate formation in the colon, has been shown to decrease skatole synthesis. Butyrate produced by bacterial fermentation in the colon has been shown to inhibit mucosal apoptosis (Mentschel and Claus, 2003) and thereby reduce the availability of endogenous tryptophan available for skatole production.
Antibiotic growth promoters have been shown to reduce microbial activity in the gastro-intestinal tract and to reduce the concentration of skatole in feces of gilts and entire male pigs (Hawe et al., 1992, Hansen et al., 1997). In January 2006, their use was prohibited in the European Union due to concerns about bacteria resistance to antibiotics. Organic acids have received much attention as an alternative and considerable research confirms positive effects on growth performance in all classes of pigs (Roth and Kirchgessner, 1998, Partanen and Mroz, 1999, Witte et al., 2000). Organic acids have shown to modify bacterial populations in the gastro-intestinal tract of pigs (Bolduan et al., 1988, Øverland et al., 2000, Canibe et al., 2001).It would be of interest to investigate whether the addition of organic acid to diets would reduce skatole synthesis in entire male pigs and reduce the boar taint problem of the meat. Furthermore, the effect of adding butyrate directly to diets on skatole production in hindgut has not been investigated. A study was designed to investigate the effect of different organic acids (formic acid, benzoic acid, sorbic acid, and butyrate) in diets of entire male pigs on 1) growth performance and carcass quality, 2) microbiota in gastro-intestinal tract, 3) skatole, indole, and organic acid levels in colonic digesta, and 4) skatole, indole, and androstenone concentration in blood plasma and adipose tissue.
Section snippets
Materials and methods
One feeding experiment evaluated different organic acids in diets of entire male pigs at the Experimental Farm of the Norwegian University of Life Sciences.
Health
The pigs had a good health status. No health problems related to the dietary treatments were encountered during the experimental period. One pig from the group with benzoic acid diet was euthanized due to severe vomiting and appetite failure. No abnormalities were revealed at necropsy. One pig was removed from the sorbic acid diet due to paralysis in the hind legs caused by initial tail biting and secondary bacterial infection of the lower spine.
Androstenone, skatole, indole, and organic acid levels
There were no significant differences in the
Discussion
The main objective of this study was to evaluate the effect of organic acids (formic acid, benzoic acid, sorbic acid and butyrate) on the production of skatole in the gastro-intestinal tract of entire male pigs. Organic acids have shown to exert an antimicrobial effect in the gastro-intestinal tract of pigs (Eckel et al., 1992, Gedek et al.,1992, Maribo et al., 2000). It was therefore hypothesized that organic acids would suppress the skatole forming bacteria in the hind-gut of the entire male
Conclusion
Supplementing diets with formic acid, benzoic acid, sorbic acid, or normal coated or inulin coated butyric acid did not affect skatole or indole levels or organic acid levels in colon of entire male pigs. Formic acid or benzoic acid supplemented diets resulted in lower plasma skatole levels than the control or the sorbic acid supplemented diets. Adding formic acid, benzoic acid, sorbic acid to diets for entire male pigs reduced microbial population in the gastro-intestinal tract, but this did
Acknowledgements
We thank Mr. Frank Sundby, Mr. Claes-Gøran Friedstedt, and Ms. Anne-Marie Grønvold for their technical assistance in sampling and analyses. We also thank the pig house staff and the staff at the microbiological laboratory for their help. This study was supported by grant # ES122080 “Male pigs — feeding, husbandry and environment” from the Research Council of Norway.
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