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.