Traceability of lamb production systems: carotenoids in plasma and adipose tissue

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Abstract
This study was conducted to determine whether carotenoid pigments can act as biomarkers of grass feeding to trace lamb production systems. Three production systems were compared: G = grazing (72 lambs), S = stall-feeding (26 lambs), and GS = grazing period followed by a stall-feeding period (27 lambs). Presence of carotenoids in tissues was evaluated by plasma concentration and reflectance spectrum of subcutaneous caudal adipose tissue. Plasma carotenoid content was measured during the grazing period for G and GS lambs, at the end of the grazing period for GS lambs and at slaughter for G, S and GS lambs. Reflectance spectrum of adipose tissue was measured at slaughter for 38 G and 26 S lambs. We collected 135 G and 26 S blood samples. Carotenoids were detected in 97% of the G blood samples, whereas they were not detected in 93% of the S blood samples. Plasma carotenoid content of all the GS lambs decreased during the stall-feeding period. Mean reflectance spectra of adipose tissue of G and S lambs differed between 450 and 510 nm, which corresponds to light absorption by carotenoids. We performed a mathematical analysis of the spectrum in order to quantify absorbance in this zone and to propose an index that can be used in the meat industry to trace animal production systems. This method was less discriminating than plasma carotenoid analysis, as there was some overlapping in the frequency distribution of the traceability index for G and S lambs that concerned 19% of the lambs. Sensitivity of the two methods to bias and applicability to cattle are discussed.