Postprandial indole and skatole formation in the rumen when feeding white clover, perennial ryegrass and Lotus corniculatus

摘要

In some international markets, meat and milk products from pasture-fed animals is associated with an undesirable pastoral flavour and odour. Sensory evaluation and chemical analysis of products has associated these flavours and odours with the presence of skatole and indole. Skatole and indole are formed in the rumen from the degradation of dietary protein. Condensed tannins (CT) have been shown to reduce protein degradation in the rumen and could reduce the formation of skatole and indole. This study investigated the concentrations of skatole and indole in the rurnen of sheep after feeding white clover (WC), perennial ryegrass (PRO) and the CT forage, Lotus corniculatus (LC). Six rumen-fistulated Romney wethers were fed the cut forages and rumencontents sampled at intervals after the start of feeding. Feeding WC resulted in higher (P<0.05) peak concentrations of indole and skatole in the rumen per kilogram of crude protein eaten (CPI) compared to PRO and LC. There was a higher peak concentration of indole, but not skatole, in the rumen of sheep fed PRO compared to sheep fed LC (P<0.05). Feeding LC resulted in lower peak concentrations of skatole compared to feeding WC and lower peak concentrations of indole than when feeding WC or PRO. White clover in pastures may be a key factor of the high skatole and indole contents in meat and milk products obtained from pasture-based grazing systems. CT forages seem a likely solution to reducing ruminal skatole and indole formation.