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).