3.1 | Fatty acid composition of longissimus dorsi
The relative contents of muscle FAs obtained from the 39 lambs and the corresponding statistical analysis are shown in Table 2. The highest percentage FA was oleic acid (C18:1n9), ranging from 33.49% (grazing group) to 37.93% (stall feeding group). All FAs, with the exception of SFA (C10:0, C12:0, C14:0, C17:0), MFA (C14:1, C16:1, C24:1, C22:1n9), PUFA (C20:2, C18:2n6), significantly varied across the three feeding modes (Table 2). The grazing treatments for 4 h or 12 h increased (P < 0.01 or P < 0.05) the proportions of SFAs (i.e., C13:0, C18:0, C21:0, C22:0, C23:0, and C24:0), but resulted in a lower (P = 0.002) C16:0 proportion compared to the control group. In addition, lower (P = 0.012) proportions of C18:1n9 were found in the grazing and time-limited grazing treatments. The effect of the feeding regime on the FA content was calculated, and the data indicated that the grazing treatments clearly improved almost all PUFAs. For example, the grazing treatment had the highest proportions of C18:3n3 (α-linolenic acid, ALA) and C20:5n3 (timnodonic acid, EPA) compared to the other two treatments (P < 0.001). Compared to the other feeding modes, the grazing treatment had a higher (P < 0.001) proportion of C22:6n3 (docosahexaenoic acid, DHA) than the other treatments, which were not significantly different from each other. The grazing treatment had the highest (P = 0.041; P = 0.004) proportions of C20:3n6 and C20:4n6 and tended (P = 0.102) to have increased C18:2n6. Compared with the control, the sum of n-3 polyunsaturated fatty acids (PUFAs) was markedly increased, and the ratio of n-6/n-3 was decreased from 17.11% to 7.69% after grazing for 4 h or 12h (P < 0.001).