Feed interventions and skatole deposition

Abstract

Skatole produced in the large intestine of the pig and the testicular steroid androstenone are the main substances contributing to boar tainted meat from entire male pigs. Boar taint decreases the quality of the meat and is not accepted by consumers. Until now boar taint has been avoided by castrating male pigs. Surgical castration reduces lean meat percentage, growth rate and feed efficiency, and it causes pain to the animal. This constitutes a problem in relation to productivity and welfare. Different attempts on avoiding surgical castration were either not fully effective, not accepted by the market, or they have a long time horizon for implementation. However, when focusing on the effect of feed interventions on boar taint, previous studies have showed a reducing effect through reduced skatole production in the large intestine after a one week application period. Skatole is produced from the microbial fermentation of L-tryptophan in the large intestine. In the literature it is well documented that skatole production in the large intestine is positively correlated with skatole deposition in adipose tissue. Moreover skatole production can be decreased by adding non-digestible and easy fermentable carbohydrates to the feed. However, little is known about skatole producing bacteria from the large intestine of pigs, and how these bacteria can be affected. This thesis reviews skatole production and metabolism in the pig, and how skatole production can be reduced by affecting the microbial production of skatole in the large intestine. A skatole producing bacterium SK9 K4 was isolated from the gastrointestinal tract of pigs. No such bacterium has previously been described. The bacterium was characterised by 16S RNA sequencing, gram stain, analysis of DNA G-C content, cellular fatty acids composition and DNA hybridisation with closely related bacteria. The fermentation of different carbohydrate sources, the growth pattern, the production of organic acids and the skatole production were studied in vitro. The production of skatole in the large intestine was correlated with skatole deposition in adipose tissue. Skatole production could be reduced when adding a minimum of 20 % raw potato starch or 9 % inulin to the feed. The problem concerning deposition of skatole in adipose tissue seems to be solved through the introduction of feed interventions. However high concentrations of androstenone deposited in adipose tissue remains a challenge. Thus, the feed interventions were not fully effective against boar taint. SK9 K4 was described as cells being strictly anaerobic, occurred singly or in pairs and were gram positive. It was identical with an Olsenella sp. strain isolated from the rumen, an uncultured Olsenella sp. clone isolated from sludge and an uncultured bacterium colon isolated from the oral cavity. Moreover SK9 K4 was closely related to Olsenella uli, Olsenella profusa, Olsenella umbonata and Atopobium parvulum. SK9 K4 and O. uli produced skatole from idole-3-acetic acid but not from L-tryptophan. The major fermentation products were lactic acid together with acetic acid and formic acid. SK9 K4 was not able to ferment raw potato starch, inulin and raw corn starch. Thus, when feeding resistant starch or inulin, the growth of skatole producing bacteria might be reduced followed by a reduced ability to produce skatole. The characterisation of a skatole producing bacterium isolated from the gastrointestinal tract of pigs gives the opportunity to further study the bacterium in vivo. Studies should be conducted to investigate the effect of a control diet compared to a diet added a non-digestible and easy fermentable carbohydrate on the growth of SK9 K4 in the large intestine of the pig