## 1 Introduction  
China is the largest producer and consumer of mutton in the world with a production level of 4.92 million tons in 2020. In recent years, the demand for lamb meat has increased with economic development and the changing consumption preference of meat products. Meanwhile, consumers are paying more attention to meat quality due to the implications of meat composition for human health [1, 2]. Many factors affect the organoleptic qualities and acceptability of lamb meat, such as sex, age, breed, and feeding systems [3, 4, 5]. Among these factors, feeding systems have been shown to play an important role in the regulation of meat quality. Current sheep feeding systems including outdoor grazing and indoor supplementary feeding, of which grazing is believed to be the cheapest method for lamb production and can also provide meat with the 'green' image as perceived by consumers [6]. It has been confirmed that grazing pastures can produce healthier lamb meat with higher accumulations of conjugated linoleic acids and _n_-3 polyunsaturated fatty acids and lower levels of saturated fatty acids and _n_-6/_n_-3 compared to meat from lambs that were fed a concentrate-based diet [7]. However, lambs under pure grazing management showed lower production performances compared to those that were fed a concentrate-based diet due to the low nutrient values in pastures [8]. Additionally, overgrazing results in a decrease in grassland productivity and damages the ecological balance, especially in desert or semidesert areas [9]. In contrast, supplemental feeding can improve the rate of live weight gain and produce heavier carcasses from the grazing livestock [10]. However, supplementation of commercial feed in the diet results in lower quality of lamb meat, such as higher contents of saturated fatty acids, cholesterol, and lower polyunsaturated fatty acids, improving the risk of an atherogenic potential in humans [11] and coronary heart disease [12]. Supplementation with concentrate could improve some indexes of meat quality such as the L* (lightness) value of meat [13; 14]. These studies suggested that the lamb feeding systems face a contradiction between higher meat production with lower meat quality by indoor feeding and higher meat quality with lower production as well as the increase in environmental pressure by grazing. A restricted grazing time system, which means giving the lamb constant grazing time on the grass ground per day with corresponding supplementary feed, can guarantee lambs both access to pastures and abundant energy requirements from supplemented concentrate. The effects of restricted grazing time systems on the pasture intake, productivity, and grazing behavior of dairy cows [15] and sheep [16] have been studied. Previous research has reported the effects of restricted grazing time systems on the foraging behavior, dry matter intake, weight gain, and other performances of growing lambs and grassland production [9; 17; 18]. The results indicated that moderate grazing time with the appropriate supplemental concentrate diet is a better way to manage lamb production when considering the growth performance of lambs and the productivity of the grasslands. In addition, our previous study showed that reasonable grazing with supplementary feeding can improve the fatty acid composition of lamb meat [19]. However, few reports have evaluated the influence of the restricted grazing system on the carcass traits and meat characteristics of growing lambs in a desert steppe. Moreover, meat flavor is one of the important attributes of meat quality, plays a key role in influencing consumers' acceptability of meat, and is closely associated with the volatile profile of meat [20; 21]. Tan lamb is very popular among consumers because of its unique flavor and delicious meat quality. Tan lambs were traditionally raised in the desert and semidesert areas of Ningxia Hui Autonomous Region, in the northwest of China. However, limited studies have been undertaken on the relationship between meat flavor and feeding systems in Tan lamb.