Stable Isotopes to Discriminate Lambs Fed Herbage or Concentrate both Obtained from C3 Plants

This study was aimed at determining whether isotopic ratio mass spectrometry (IRMS) enables us to discriminate between lambs fed herbage or concentrate, both obtained from C3 plants, and those fed a concentrate obtained from C4 plants. Thirty-four Comisana male lambs (age 45 days) were assigned to three feeding treatments. Fourteen lambs were fed vetch (Vicia sativa) ad libitum. Another fourteen lambs received a barley-based concentrate. The remaining six lambs were fed a maize-based concentrate. After 60 days of experimental treatment the animals were slaughtered and the wool, perirenal fat and muscle longissimus dorsi were sampled. The d13C and d15N values of the muscle, wool and feed were measured by continuous flow elemental analysis (CF-EA)-IRMS. The d13C of the fat was determined likewise. The isotopic composition of the tissues reflected that of the three diets. For the lambs which were fed herbage the muscle d13C values were higher (P<0.0005) and d15N values were lower (P<0.0005) than those of the lambs receiving concentrates. The d15N and d13C values in the muscle and d13C values in the adipose tissue allowed perfect discrimination between the lambs fed the three different diets. The regression between the d13C values measured in muscle and in wool of lambs was linear (R2 =0.99; P