1 | INTRODUCTION
With the global demand for healthy foods increasing, sheep meat
production and consumption are gaining greater importance worldwide.
Sheep production in the form of meat (lamb or mutton) makes a
significant contribution to the economic activity of many countries.
Consumers require meat that is safe, of consistent eating quality,
healthy, and convenient (Nuernberg, Fischer, Nuernberg, Ender, &
Dannenberger, 2008). The consumers’ preference for sheep meat is mainly
due to its nutritious features and healthy fatty acid composition (de
Andrade et al., 2017).
Indeed, sheep meat is one of the major sources of long-chain n-3
polyunsaturated fatty acids (PUFAs) in human diets along with fish, fish
oils, and eggs (Beng et al., 2016).
The
n-3 PUFAs, mainly alpha-linolenic acid (ALA, C18:3n3),
eicosapentaenoic
acid (EPA, C20:5n-3), and
docosahexaenoic
acid (DHA, C22:6n-3), are beneficial to human health (Aglago et al.,
2020). These beneficial n-3 PUFAs have significant roles in maternal and
childhood brain development, optimal cardiovascular function, and
retinal functions (Pewan et al., 2020). The composition of meat fatty
acids in grazing sheep strongly differs from that of sheep raised under
barn feeding conditions. Pasture feeding can promote absorption and
deposition of C18:3n3 from grass in the intramuscular tissue and can
decrease the ratio of n-6/n-3 fatty acids compared to concentrate
feeding (Nuernberg, Fischer, Nuernberg, Ender, & Dannenberger, 2008;
Zhang, Jin, Badgery, & Tana, 2017). While some studies have
investigated fatty acid variation in different feeding systems, little
is known about the association between dietary diversity and variability
in fatty acid composition.
Quantitative estimates of dietary composition of herbivores in the
context of complex plant distribution in the grassland are essential to
determine herbivore-herbage preference and to investigate the
relationships between performance of herbivores and their diets.
Measuring the diet choices of grazing animals presents several
challenges complicating the evaluation of feed efficiency in grassland
ecosystems (Vargas Jurado et al., 2019). Traditionally, diet analyses of
grazing herbivores have been conducted through n-alkanes and long-chain
alcohols of plants detected from animal feces (Zhang et al., 2019).
However, their use in identification of diet items of grazing herbivores
is not always accurate (Lin et al., 2012; Narvaez, Brosh, & Pittroff,
2012). Application of a molecular approach to quantify the diet
composition can lead to greater understanding of how changes in the diet
affect production (Pompanon et al., 2012; Kowalczyk et al., 2019;
Waraniak, Marsh, & Scribner, 2019). Metabarcoding has been suggested as
a useful tool for determining animal diets due to its greater accuracy
and resolution (Bhattacharyya, Dawson, Hipperson, & Ishtiaq, 2019).
Metabarcoding is conducted through utilizing conserved gene regions to
amplify sequences in samples that are unique in different taxa (King,
Read, Traugott, & Symondson, 2008). Still, the use of metabarcoding to
study diets of grazing herbivores has been relatively limited.
Here, we focus on the applicability of dietary metabarcoding as a
sampling tool for examining the diet composition of Tan sheep grazing in
a desert grassland. Additionally, we evaluated the effects of grazing
type compared to concentrate feeding on muscle fatty acid composition,
particularly n-3 PUFAs, in the longissimus dorsi (LD). This study
also explored herbage-PUFAs correlation profiles in lambs through
systematic correlation analyses. The results provide an initial view of
herbage-PUFAs
association
in fatty acid accumulation that will promote further understanding of
the flavor-relevant deposition process.