Concentration of indoles and other rumen metabolites in sheep after a meal of fresh white clover,perennial ryegrass or Lotus corniculatus and the appearance of indoles in the blood

The objective of this study was to determine the effect of feeding three fresh forage diets, white clover (WC), perennial ryegrass (PRG) and Lotus corniculatus (LC), on the formation of indole and skatole in the rumen of sheep. The formation of indole and skatole in the rumen and their appearance in the blood were also compared. Peak rumen indole and skatole concentrations per kg crude protein intake (CPI) were significantly higher when feeding WC compared with PRG and LC (P < 0.05) and this was associated with a significantly higher rumen concentration per kg CPI of ammonia, branched chain volatile fatty acids, total nitrogen and soluble nitrogen (P < 0.05). Greater indole and skatole concentrations when feeding WC can be attributed to high solubility and rapid degradation of the forage protein. LC had a similar nutrient composition to WC, but the condensed tannins in LC slowed protein degradation and reduced indole and skatole formation. Indole and skatole concentrations peaked in the plasma 1–2 h after the end of feeding, indicating that skatole and indole are rapidly absorbed from the rumen into the blood. High indole and skatole formation with low intakes of WC indicates that the WC component of traditional New Zealand pastures may be the primary cause of undesirable pastoral flavours that result from the presence of indoles in meat. To ameliorate undesirable flavours, producers reliant on pastoral systems will need to consider using alternative forages such as LC to reduce protein solubility and degradation rate. Copyright © 2007 Society of Chemical Industry