Twenty pregnant Comisana ewes were divided into two groups of 10. One group was allowed to graze a vetch pasture (grass). The second group of animals was housed collectively in a pen and was given hay and concentrates (concentrate). After lambing, all the ewes were allowed to stay with the respective lambs between 18:00 h and 07:00 h of the following day in two different pens. Therefore all the lambs were raised exclusively on maternal milk. The lambs were slaughtered at 38 days of age. Milk and lamb meat (longissimus dorsi muscle) fatty acids were analysed. Ewes on grass produced milk with a lower (P < 0·001) proportion of saturated fatty acids and with a higher proportion of both monounsaturated (P < 0·05) and polyunsaturated fatty acids (P < 0·01) than ewes given concentrates. Trans-vaccenic acid was significantly higher (P < 0·001) in milk from grass-fed animals compared with ewes given concentrates. Linoleic acid (C18: 2 n-6) tended to be higher (P = 0·06) in milk from ewes on concentrates while linolenic acid (C18: 3 n-3) was significantly higher (P < 0·001) in milk from animals grazing pasture. Conjugated linoleic acid (cis-9, trans-11 C18: 2) was almost double in milk from grass-fed ewes compared with animals given concentrates (P < 0·001). Regarding lamb tissue, trans-vaccenic acid (C18: 1 trans-11) was higher (P = 0·01) in the fat from lambs raised by grazing ewes. Linoleic acid (C18: 2 n-6) was at higher concentration (P < 0·001) in the fat from lambs raised by ewes given concentrates. Linolenic acid (C18: 3 n-3) was increased three-fold (P < 0·001) in the fat of lambs from the grass group compared with lambs suckled by ewes given concentrates. The isomer cis-9, trans-11 of conjugated linoleic acid was present at double concentration (P < 0·001) in the fat from animals raised by grazing ewes. Eicosapentaenoic (C20: 5 n-3; EPA) and docosaesaenoic (C22: 6 n-3; DHA) acids were higher (respectively P < 0·001 and P = 0·01) in the intramuscular fat from lambs from the grass group compared with animals from the concentrate group. The n-6/n-3 ratio was lower (P < 0·001) in the meat from lambs raised by grazing ewes. Overall this trial showed that ewe feeding system strongly affects intramuscular fatty acids even in lambs raised exclusively on maternal milk.

Carotenoid pigments are good biomarkers of grass-feeding in sheep. However, as grazing lambs may be concentrate-finished, we investigated the effect of concentrate finishing after grazing on the carotenoid concentration of fat in sheep, and its significance for discriminating lamb production systems. In experiment 1 with 32 lambs, four feeding treatments were compared: G = grazing, C = feeding a concentrate-based diet, GSC = short concentrate-finishing period after grazing, and GLC = long concentrate-finishing period after grazing. The concentrate supply was regulated to have similar average daily gain for all treatments. In experiment 2, 42 ewes were given a low carotenoid diet after pasture feeding, for 0, 8, 22, 42, 84 or 126 days. The feeding level was adjusted to maintain body weight and body condition score. The nature and concentration of carotenoids was analysed by HPLC on diets and lambs’ perirenal fat. The reflectance spectrum of perirenal fat was measured at slaughter. Lutein was the only carotenoid in lamb fat. In experiment 1, the intensity of light absorption by lutein was linearly related with its concentration in the fat (P < 0·001) and was negatively correlated with the duration of the finishing period. The design of experiment 2 avoided the confounding effect of fat gain during the finishing period and examined the effect of the duration of this period by itself. There was no effect of stall-feeding duration on the intensity of light absorption by carotenoids in the fat in experiment 2, demonstrating that the effect of stall-feeding duration in fattening lambs was mediated via a dilution of existing fat with whiter fat rather than through pigments coming out of the fat. The concentration of lutein and the intensity of its light absorption in the fat decreased with lamb body-weight gain during the finishing period (P < 0·01 and P < 0·05 respectively) and increased with plasma carotenoid content at the end of the grazing period (P < 0·001). Because of the inter-individual variability in carotenoid absorption, the use of the reflectance spectrum of the fat alone may cause some concentrate finished grazing lambs to be classified as C lambs shortly after the beginning of the stall-feeding period, whereas others may be considered as G lambs for a long period of time. However, the combined use of plasma carotenoid content at slaughter together with the reflectance spectrum of the fat improves reliability in the discrimination of grass-fed, concentrate-fed and concentrate-finished grazing lambs, by taking advantage of the differences in the rate of reduction in carotenoid concentration in blood and fat.

The research was carried out to evaluate the effect of different dietary α-tocopheryl acetate (DTA) concentrations in light-weight lambs on muscle α-tocopherol accumulation and on quality characteristics of stored meats. Thirty-two Manchego lambs were randomly distributed to four groups and given diets containing four levels of DTA (20, 270, 520 and 1020 mg/kg diet) for 6 weeks. Lambs were slaughtered at live weights ranging from 23·5 to 26·4 kg. A linear (P < 0·001) and quadratic (P < 0·001) effect of dietary supplementation level was observed on muscular α-tocopherol concentration, which fitted the following equation: mg muscle α-tocopherol per kg muscle = 1·78(s.e. 0·18) + 7·08 (s.e.0·89)(1 - e00012DTA)) (P < 0·001, R2 = 0·99). There was a linear effect (P < 0·001) of muscle vitamin E concentration on thiobarbituric acid reactive substance on day 0 of storage, but a linear plus quadratic effect (P < 0·001) on days 3, 6 and 9. Broken line analysis of data at day 9 of storage indicated a target muscle α-tocopherol concentration of 5·4 mg/kg. Evolution of surface redness of lamb chops also showed a linear and quadratic effect of dietary treatment on days 3 and 6 of storage, but only a linear effect on day 9. Broken line analysis of data at 3 and 6 days indicated a target α-tocopherol concentration in the range 5·3 to 5·6 mg/kg muscle for optimum red colour stability. Surface luminosity showed no effect of dietary treatment at days 0, 3 and 6 of storage but a linear (P < 0·01) plus quadratic (P < 0·05) effect on day 9 of storage. Broken line analysis at this point indicated a target muscle α-tocopherol concentration of 3·2 mg/kg. It is concluded that the effectiveness of dietary α-tocopheryl acetate supplementation depends on the meat quality attribute assessed. A significant positive effect for lipid oxidation can be reached even at the lower supplementation level utilized in this experiment (270 mg/kg diet). However, considering the protecting effect at different storage times and particularly the effect on meat surface redness, the optimum level would be in the range 5·3 to 5·6 mg/kg muscle, which correspond to a dietary inclusion of 550 to 625 mg α-tocopheryl acetate/kg diet.

Near infrared reflectance spectroscopy (NIRS) was used to study the reflectance properties of intact and minced lamb muscles in two presentations to the instrument to predict their chemical composition. A total of 306 muscles were examined from 51 lambs, consisting of the following muscles: longissimus dorsi, supraspinatus, infraspinatus, semimembranosus, semitendinosus and rectus femoris. Modified partial least squares (MPLS) regression models of chemical variables yielded R2 and standard error of cross-validation (SECV) of 0·76 (SECV: 10·4), 0·83 (SECV: 5·5) and 0·73 (SECV: 4·7) for moisture, crude protein and intramuscular fat in the minced samples expressed as g/kg on a fresh-weight basis, respectively. Calibrations for intact samples had lower R2 and higher standard error of cross validation (SECV) compared with the minced samples.

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.