The use of subcutaneous fat colour to trace grass-feeding in Parda de Montaña yearling bulls

Abstract

Grass-feeding in calves can be traced with carotenoid pigments in fat depots. Parda de Montaña calves (227 kg) were fed concentrates (CON), grazed lucerne plus 2 kg/d barley (LUC) or had the same management as LUC calves for 3 months and were finished with concentrates for 2 months (LUC + CON) until a slaughter weight of 450 kg. A spectrophotometer was used to measure subcutaneous fat colour. The proportion of reflected light each 10 nm between 450 and 510 nm was collected to calculate the absolute value of the integral of the translated spectrum (SUM). Lightness (L*) was greater and redness (a*) was lower for CON calves than for their counterparts. On the other hand, yellowness (b*) and SUM were greater in LUC calves than in the rest of the feeding strategies, being both variables highly correlated (r = 0.69, P <0.001). Two logistic regressions were obtained to discriminate carcasses according to the fattening strategy, the first one calculated the probability of a carcass to belong to a calf that grazed in lucerne: P (LUC) = (1 + e^{18.8-5.6xL*-36.9xa* + 0.3xSUM + 29.8xC}*)-1 and the second one calculated the probability of a carcass to belong to a calf that was finished on concentrates after grazing lucerne: P (LUC + CON) = (1 + e^{833.7-11.8xL* + 4.7xa* + 0.2xSUM-2.5xC*)-1}. These regressions could be used to trace carcasses belonging to calves that had been grazing. Therefore, they could be used in abattoirs and retailers to trace grass-fed carcasses.