Effects of dietary glutamine supplementation on lipid metabolism, fatty acid composition, and taste properties in the longissimus thoracis muscle of feed-restricted yaks.

This research aimed to explore the influence of dietary Gln supplementation on serum biochemical indices, slaughter performance, the fatty acid composition, lipid metabolism, and taste properties in the longissimus thoracis muscle of feed-restricted (FR) yaks. A total of 24 healthy yaks (age 31 months and body weight 265.35 ± 25.81 kg) were randomly divided into 3 groups with 8 replicates per group and one yak per replicate. The growth experiment lasted for 60 d in two stages of 1 to 30 d and 31 to 60 d after 15 d of pre-feeding. In the pre-feeding period, all yaks were fed a basal diet ad libitum and the dry matter intake (DMI) was recorded. The yaks in the control (Con) group were fed the basal diet ad libitum during d 0 to 60. The yaks in the feed restriction (FR) group were fed 50% DMI of the pre-feeding period during d 0 to 60, and the yaks in the feed restriction + glutamine (FR + Gln) group were fed 50% DMI of the pre-feeding period during d 0 to 30, and were fed 50% DMI of the pre-feeding + 1% Gln during d 31 to 60. The results showed that FR significantly decreased the average daily gain (ADG), serum triglyceride (TG) concentration, and backfat thickness (BT), as well as intramuscular fat (IMF) content, C18:2n6c, n-6 polyunsaturated fatty acids (PUFA), and PUFA levels in the longissimus thoracis muscle (P < 0.05). However, dietary Gln supplementation significantly increased the ADG from 31 to 60 d, serum TG concentration, BT, and IMF content, as well as up-regulated the expression of the lipid synthesis-related genes acetyl-coa carboxylase (ACC), fatty acid synthase (FAS), peroxisome proliferator-activated receptor α (PPARγ), and sterol regulatory element binding transcription factor 1 (SREBP1), and down-regulated the expression of the lipid breakdown-related genes adipose triglyceride lipase (ATGL) and hormone-sensitive triglyceride lipase (HSL) (P < 0.05). Moreover, dietary Gln supplementation also improved the C18:2n6c, PUFA, and n-6 PUFA levels (P < 0.05). Besides, Gln alleviated the reduction in the umami intensity of the longissimus thoracis muscle of FR yaks (P = 0.019). Mechanistically, the endoplasmic reticulum stress (ERS) might be involved in Gln alleviating the FR induced disturbances in lipid metabolism. These results indicated that Gln alleviated the ERS induced by FR, and relieved the changes in fat deposition, fatty acid composition, and umami intensity.