Fat color and reflectance spectra to evaluate the β-carotene, lutein and α-tocopherol in the plasma of bovines finished on meadows or on a dry total mixed ration

• Visible and near infrared spectra of plasma is useful in discriminating steers fed with different diets.
• Visible and near infrared spectra of the plasma is not suitable for discriminating between breeds.
• Calibration of β-carotene plasmatic concentration was useful for analytic purposes.
• Fat color was useful to discriminate carcasses from different diets.

An experiment was conducted to analyze the evolution of carotenoids and α-tocopherol during the fattening period of beef cattle that were fed with different diets to check the feasibility of using these compounds to trace grass-feeding in the visible and near-infrared spectra. A group of Parda de Montaña and a group of Pirenaica steers were finished on mountain meadows, and another group of Pirenaica steers was finished with a dry total mixed ration (50 alfalfa hay:10 straw:40 maize grain, as-such basis). Plasma samples were obtained throughout the fattening period to determine the β-carotene, lutein and α-tocopherol concentrations via high performance liquid chromatography (HPLC) and plasma visible-near infrared (VIS-NIR) spectra; the samples were collected using the dry-extract system for infrared (DESIR) method. Additionally, after slaughter, the carcass subcutaneous fat color was measured, and a spectrophotometric estimation of the carotenoid content was calculated. Feeding systems had a great effect on the plasma concentrations of β-carotene, lutein and α-tocopherol, which increased sharply when the animals were grazing. In the same way, when the animals were switched over to the dry total mixed ration, their concentrations sharply decreased to quite low concentrations. Both the VIS-NIR spectra of the plasma and the subcutaneous fat color are useful in discriminating steers fed with finishing diets, but neither method is not suitable for discriminating between the Pirenaica and Parda de Montaña breeds. The calibrations that were developed to estimate the lutein and α-tocopherol concentrations could be classified as poor. The calibration used to estimate the β-carotene plasma concentration was useful for analytic purposes, but it should still be improved. The DESIR method can be interesting to monitor the plasma concentrations of carotenoids and tocopherol in live animals, whereas the measurement of the subcutaneous fat color of the carcass is a simple and fast method for discriminating, post-mortem, animals that were fed diets with different carotenoid contents.