Discriminação de sistemas de alimentação em ovinos através da concentração de carotenóides no tecido adiposo e no plasma

Abstract

The meat and milk from grass-fed ruminants contains more conjugated linoleic acid (CLA), vitamin E, omega-3 fatty acids, beta-carotene, and vitamin A than meat and milk from grain-fed animals. Considering this there is a need for a method capable to differentiate between grass- and stall-fed animals. In article 1 (experiment 1 and 2), our objectives were to investigate (i) the dose-response curve relating carotenoid pigments concentration in blood and fat to carotenoid intake level in lambs, (ii) how far incorporating dehydrated alfalfa in stall-fed lambs diets could affect the discrimination reliability between concentrate-fed and grass-fed lambs based on plasma and fat carotenoid assay. In experiment 1, six treatments were compared in individually penned lambs: feeding 0, 250, 500, 750, 1000 and 1250 g of dehydrated alfalfa per day for 60 days before slaughter. Each treatment (T0, T250, T500, T750, T1,000 and T1,250) had eight male Romanov x Berrichon lambs. In experiment 2, a total of 33 male Romanov x Berrichon lambs were kept grazing a natural pasture maintained in a leafy green vegetative stage and offered ad libitum for at least 59 days until slaughter. Total carotenoids plasma content was measured at slaughter by spectrophotometry. Reflectance spectrum and lightness (L*), redness (a*), and yellowness (b*) were measured after 24h of shrinkage in the perirenal and in the subcutaneous caudal fat. The translated spectrum was calculated between 450 and 510 nm (i.e., the range of light absorption by carotenoids). Reflectance measurement was replicated five times, from which we calculated the absolute value of mean integral (AVMI). In article 2, our objective was to validate in a large number of animals the use of plasma carotenoid concentration and mathematical analysis of reflectance spectrum of fat between 450 and 510 nm to discriminate pasture-fed and stall-fed lambs and, also, to explore the potential xvii use of reflectance spectrum of fat using the whole reflectance data in the zone from 400 to 700 nm. A total of 307 Limousine lambs were used for this experiment. In article 1 (experiment 1), plasma carotenoid concentration at slaughter (PCCS) increased linearly with mean daily carotenoid intake (MDCI, P < 0.001). Both subcutaneous caudal and perirenal fat AVMI increased linearly (P < 0.001) with MDCI and PCCS, the slope of the regression being greater for perirenal than for subcutaneous caudal fat (P < 0.05 and P < 0.005 respectively). PCCS was greater for lambs in the experiment 2 than the ones in the experiment 1 (P < 0.001). We established the dose-response curves relating PCCS and AVMI of subcutaneous and perirenal fat to carotenoid intake level. We showed that the combined use of plasma carotenoid concentration at slaughter and perirenal fat AVMI enabled to discriminate pasture-fed lambs from lambs receiving up to 500 g dehydrated alfalfa per d. In article 2, the plasma carotenoid concentration method correctly classified 97.01% of lambs. The performance of classification using the reflectance spectrum between 400-700 nm was better than at 450-510 nm (P < 0.0001). The difference between feeding treatments was, however, greater for perirenal than for subcutaneous caudal fat (P = 0.0001), and also greater for measurements made after 24h shrinkage than those obtained at 0 h (P < 0.0001).