Skatole and indole concentration and the odour of fat from lambs that had grazed perennial ryegrass/white clover pasture or Lotus corniculatus

An experiment was conducted for 111 days in the summer of 2002/2003 to compare the effect of grazing lambs on condensed tannin-containing Lotus corniculatus L. (cv. Grasslands Goldie; n = 12) and perennial ryegrass/white clover pasture (PRG/WC; Lolium perenne/Trifolium repens; n = 12) on the concentration of indole and skatole in rumen fluid, blood plasma and body fat and upon the odour of the fat. Rumen fluid and blood samples were obtained on days 0, 22, 58, 87 and 111 of the experiment. Fat from inter-muscular and tail-stub depots was obtained at slaughter. During the experiment the mean concentration of indole and skatole in both the rumen fluid and blood plasma was lower for lambs grazing L. corniculatus compared to PRG/WC pastures. The concentration of skatole in the tail-stub fat was lower and less variable (P<0.05) in the lambs that had grazed L. corniculatus. No differences were observed in the odour of the inter-muscular fat from lambs that had grazed L. corniculatus compared to PRG/WC pasture, suggesting that the reductions in indole and skatole formation from grazing L. corniculatus were not large enough to produce a detectable difference in fat odour. The experiment was complicated by the on-set of drought conditions during the second half which resulted in a relatively lower level of crude protein in the L. corniculatus forage. It was concluded that CT-containing forages hold some potential to reduce the concentration of indole and skatole in the fat to provide consistently flavoured meat products from grazing systems.