Visible spectroscopy on carcass fat combined with chemometrics to distinguish pasture-fed, concentrate-fed and concentrate-finished pasture-fed lambs.

We used visible spectroscopy of fat to discriminate lambs that were pasture-fed (n=76), concentrate-fed (n=79) or concentrate-finished after pasture-feeding (n=69). The reflectance spectrum of perirenal and subcutaneous caudal fat was measured at slaughter and 24h post mortem. In Method 1 (W450-510), the optical data were used at wavelengths in the range of 450-510nm to calculate an index quantifying light absorption by carotenoids. In Method 2 (W400-700), the full set of data at wavelengths in the range of 400-700nm was used to differentiate carcasses using PLS-DA as a classification method. W400-700 proved more reliable than W450-510 (P<0.0001). The proportion of correctly classified lambs using W400-700 was 95.6% and 95.9% for measurements made on perirenal fat at slaughter and 24h post mortem. The intensity of light absorption by carotenoids decreased exponentially with live weight gain during the finishing period.