Fat volatiles tracers of grass feeding in sheep

Volatile compounds were analysed in subcutaneous fat from lambs raised and finished on grass (GG); raised and finished on concentrates (SS); raised on grass and finished on concentrates for a long (GS1) or a short (GS2) period. Whereas 3-methylindole (skatole), a compound that has been described as a good discriminator of grass feeding, was unaffected by the diet (P>0.05), 2,3-octanedione was lower (P<0.01) in the fat from animals that spent a period in stall with a concentrate diet than in those finished on grass. Among the 20 monoterpenes detected, only p-cymene was affected by the treatment, being higher (P<0.05) in the fat from animals raised and finished on grass (GG) than in the other treatments. Eight among the 13 detected sesquiterpenes were affected by the diet treatment. In particular β-caryophyllene, not detected in the fat from animals raised and finished on concentrates (SS group), was at basal levels in the animals raised on pasture and finished for different durations on concentrates (GS1 and GS2 treatments) and was present at high levels in the animals raised and finished on grass (P<0.0005). From a factorial discriminant analysis, four of the 33 terpenes detected discriminated perfectly those animals raised and finished on pasture (GG) from all the other groups (SS, GS1, GS2).