Variations in stable isotope ratios in lamb blood fractions following dietary changes: a preliminary study

In meat production it is common practice to use finishing diets based on concentrates, even for those animals previously raised on pasture. No studies have investigated the variations of stable isotope ratios in lamb plasma and erythrocytes, following a switch from pasture to a concentrate-based diet during the last days before slaughter. For meat traceability it is important to verify how and whether these parameters are affected in blood fractions.

Blood of ten male Italian Merino lambs, whose diet was switched from pasture to concentrate, was sampled 8 times (days 1, 2, 3, 4, 5, 6, 7 and 14) in the last 14 days before slaughter. The variations in the δ(13)C, δ(15)N, δ(18)O and δ(34)S values of blood plasma and erythrocytes were investigated. The stable isotope ratios of the samples were measured using a stable isotope mass spectrometer coupled with an elemental analyser (C, N, S) and a CO2/H2O equilibration system (O(plasma)).

The δ(13) C(plasma), δ(18)O(plasma) and δ(34)S(plasma) values were shown to be different 7 days after the abrupt variation in the diet. The comparison between erythrocytes and plasma stable isotope ratios could be suitable for verifying whether the animal was actually pasture-raised and could merit a higher price. The erythrocytes isotopic signature was not affected by very short finishing periods in previously grazed animals and maintained the pasture-raised fingerprint, while the analysis of plasma could detect very short finishing periods with concentrate and hay.

The present study has demonstrated that the combination of blood plasma and erythrocytes stable isotope ratios of carbon, nitrogen, oxygen and sulphur can be used to infer the dietary background of lambs and thus offers a tool for the authentication of the animal production system.