4.2 | Fatty acid deposition
This study represents our first effort to evaluate the correlations between herbage consumed and meat quality characteristics in sheep. Combining the dietary composition information with data on the deposition of muscle fatty acids has provided insights into how changes in dietary composition of grazing animals affect the fatty acid patterns in the longissimus dorsi . There was a significant alteration in the muscle fatty acid composition of the sheep as the overall diet community and biomass of plant taxa altered between the three treatments. Grazing herbivore preferences were largely dependent on the usability of plant items in the pasture. While the dietary structure or plant community of the habitat changed, feeding behavior preferences of sheep varied, and this variation might be the cause of different muscle fatty acid contents. Metabarcoding dietary analyses have provided a greater and more robust ecological context to decipher diet composition and dietary shifts.
The performance traits of grazing lambs are largely affected by nutrient components of the forage. Furthermore, the grazing feeding can promote the formation of beneficial fatty acids in sheep meat. Previous research has shown that the special flavor of lamb meat is probably mediated by short-chain fatty acids (SCFAs) and stearic acids. Compared to the control, the feeding patterns of pasture or supplementary feeding significantly improved the total n-3 PUFA in lamb meat, which has also been observed in other studies (Zhang, Jin, Badgery, & Tana, 2017). The deposition types of meat fat were further found to differ depending on the feeding regimes. In comparison with the control, a greater (P < 0.001) ALA proportion was detected in the meat of grazing lambs. ALA, as the precursor in the endogenous synthesis of EPA and DHA in animal tissues, plays a key role in the n-3 PUFAs synthesis in meat or milk (Van Elswyk, & McNeill, 2014). As expected, we found that the sheep meat derived from grazing lambs had remarkably greater proportions of EPA and DHA than the meat from the stall-fed group. It was reported that PUFAs accounted for a high ratio in the grass/forage (Figure S1) and that n-3 fatty acids were mainly synthesized in the plant chloroplasts (Watkins Jr, Mack, Sinclair, & Mulkey, 2007). Therefore, it is supposed that fatty acid profiles in lambs are associated with those of ingested herbage.
However, the deposition mechanisms of PUFAs in sheep meat are still not fully understood. As shown in Figure S1, multiple herbage taxa from field-collected plants contain plenty of PUFAs. Of those n-3 fatty acids, ALA presented a significant linear regression between the meat and dietary intake, a result that has been observed in previous studies. Comprehending the relevance of herbage ingested by sheep to the fat deposition is important for the production of high-quality meats and the regulation of meat products. The supplements of antioxidants such as PUFAs and lycopene in the diet have been shown to improve the quality of animal products. With the decreased proportion of corresponding herbage consumed by sheep, the percentage of saturated fatty acids decreased (Table 2). Therefore, we concluded that some herbage species can reduce the proportion of SFAs and consequently increase the proportion of PUFAs in the meat of sheep, thus realizing the improvement of mutton flavor. Nevertheless, the deposition of muscle fatty acids in the Tan sheep seems to be fairly insensitive to dominant herbage species such as Lespedeza and Artemisia (Figure 4 and Figure 5).