Dietary energy is crucial for ruminants’ performance and health. To determine optimal dietary energy levels for growing sheep, we evaluated their growth performance, nutrient digestibility, rumen fermentation, barrier function, and microbiota under varying metabolic energy (ME) diets. Forty-five growing Yunnan semi-fine wool sheep, aged 10 months and weighing 30.8 ± 1.9 kg, were randomly allocated to five treatments, each receiving diets with ME levels of 8.0, 8.6, 9.2, 9.8 or 10.4 MJ/kg. The results showed that with increasing dietary energy, the average daily gain (ADG) as well as the digestibility of dry matter (DM) and organic matter (OM) increased (p < 0.05), while the feed conversion ratio (FCR) decreased linearly (p = 0.01). The concentration of total VFA (p = 0.03) and propionate (p = 0.01) in the rumen increased linearly, while rumen pH (p < 0.01) and the acetate–propionate ratio (p = 0.01) decreased linearly. Meanwhile, the protein contents of Claudin-4, Claudin-7, Occludin and ZO-1 as well as the relative mRNA expression of Claudin-4 and Occludin also increased (p < 0.05). In addition, rumen bacterial diversity decreased with the increase of dietary energy, and the relative abundance of some bacteria (like Saccharofermentans, Prevotella and Succiniclasticum) changed. In conclusion, increasing dietary energy levels enhanced growth performance, nutrient digestibility, rumen fermentation, and barrier function, and altered the rumen bacterial community distribution. The optimal dietary ME for these parameters in sheep at this growth stage was between 9.8 and 10.4 MJ/kg.

The study investigated the metabolic responses of yaks to dietary net energy for gain (NEg) and metabolizable protein (MP), and explored potential biomarkers for average daily gain (ADG) in serum metabolites. A total of 40 three-year-old yaks (initial body weight = 255 ± 8.04 kg) were assigned to a 2 × 2 factorial treatment arrangement based on dietary NEg (4.18 vs 4.81 MJ/kg DM; low NEg [LE] vs high NEg [HE]) and MP (72.0 vs 82.8 g/kg DM; low MP [LP] vs high MP [HP]), comprising 4 treatments with 10 replicates each (1 yak per replicate). The yaks were fed these diets for 55 days including a 15-day adaptation period. Yaks on HP diets had greater ADG (P = 0.013) and a reduced feed-to-gain ratio (P = 0.019) compared to those on the LP diet, and those on the LE diet had greater dry matter intake (P < 0.001) but unaffected ADG compared to those on the HE diet (P > 0.05). Dietary NEg interacted with MP in relation to the apparent digestibility of dry matter (P = 0.028) and crude protein (P < 0.001). The apparent digestibility of gross energy (GE), organic matter, and neutral detergent fiber in yaks on the HE diet was greater than those in yaks on the LE diet (P < 0.05). The digestibility of GE in yaks on the HP diet was lower than those on the LP diet (P = 0.011). An significant interaction between dietary NEg level and MP level was observed on serum total bilirubin concentration, catalase concentration, and superoxide dismutase concentration (P < 0.05). Yaks fed HE diets exhibited higher serum glutathione peroxidase protein concentration (P < 0.001), but lower serum triglyceride concentration (P = 0.012) compared to those fed LE diets. Serum level of alanine transaminase was higher in yaks on the HP diet compared to those on the LP diet (P = 0.038). Untargeted metabolomics identified novel biomarkers linked to dietary NEg and MP levels, revealing that the HE diet enhanced adenosine triphosphate production through acetyl-CoA synthesis and affected amino acid, fat, and carbohydrate pathways (P < 0.05). The HP diet altered the synthesis of aromatic amino acids and vitamins (P < 0.05). Additionally, random forest analysis identified N-(9-oxodecyl) acetamide and biliverdin, as biomarkers for predicting ADG. These findings provide a theoretical foundation for the effective feeding and nutritional management of yaks.

Yaks are an important livestock species on the Tibetan Plateau, but traditional grazing practices cause a sharp drop in their weight during winter, leading to grassland degradation due to overgrazing. Although off-site fattening can improve performance and protect ecology, it often leads to a negative energy balance, liver metabolism disorders, and immune impairment due to stress. However, the effects of rumen-protected glucose (RPG) and rumen-protected taurine (RPT) on yak liver health are not yet clear. The purpose of this study was to evaluate the effects of dietary RPG and RPT levels on the growth performance, serum biochemical parameters, liver antioxidant capacity, and immunity of yaks. Twenty-eight healthy yaks weighing 170 ± 10.4 kg were randomly divided into four treatments: LGLT (RPG: 1%—low RPG [LG]; RPT: 5 g/d—low RPT [LT]), LGHT (RPG: 1%—low RPG [LG]; RPT: 20 g/d—high RPT [HT]), HGLT (RPG: 3%—high RPG [HG]; RPT: 5 g/d—low RPT [LT]), and HGHT (RPG: 3%—high RPG [HG]; RPT: 20 g/d—high RPT [HT]). The results showed that compared with the LTHT treatment group, the HGHT group upregulated the serum concentrations of glucose (p = 0.004) and Interleukin-10 (p = 0.03), the relative mRNA expression of small heterodimer partners (p = 0.01), and the sterol 12-alpha-hydroxylase (p < 0.001), while reducing the serum concentration of gamma-glutamyl transferase (p = 0.048). The serum concentration of hepatic protein carbonyl (p = 0.005) and malondialdehyde (p = 0.03) was lower in the LGHT and HGHT treatment groups than in the LGLT and HGLT groups. The relative mRNA expression of Toll-like receptor 4 (p = 0.02), Interleukin-8 (p < 0.01), and Interleukin-1β (p < 0.01) was lower in the LGHT and HGHT groups than in the LGLT and HGLT groups. Tumor necrosis factor expression was lower (p = 0.04) and glucose transporter 2 expression was higher (p < 0.01) in the HGHT group compared to other treatment groups. The expression of glucokinase, glycogen synthase, pyruvate kinase, and farnesoid X receptor was higher in the HGLT treatment group than in other treatments (p < 0.01). In conclusion, dietary supplementation with 3% PRG and 5 g/d PRT can enhance liver antioxidant capacity and immune function, reduce lipid peroxidation, and promote glucose and bile acid metabolism in yaks.

The present study evaluated the effects of dietary rumen-protected taurine (RPT) supplementation on ruminal fermentation, hematological parameters, liver function, stress-related hormones, and immune responses in yaks. Eighteen yaks were randomly allocated to three groups: a control group receiving no RPT (CON), a low-dose group receiving 20 g/day (RPT20), and a high-dose group receiving 40 g/day (RPT40). Supplementation with RPT did not significantly affect ruminal pH, microbial protein concentration, ammonia nitrogen, total volatile fatty acids, or the individual volatile fatty acid profiles (p > 0.05). A decreasing trend in red blood cell count was observed (p = 0.050), while no significant changes were detected in white blood cell or platelet indices (p > 0.05). Liver function markers, including albumin, alanine transaminase, aspartate transaminase, and total protein, remained unchanged, although a trend toward altered alkaline phosphatase activity was noted (p = 0.074). No significant effects were observed on acute-phase proteins (serum amyloid A, C-reactive protein) or stress-related hormones (epinephrine, adrenocorticotropic hormone, cortisol) (p > 0.05). Importantly, serum immunoglobulin A and immunoglobulin G levels were significantly increased in response to RPT supplementation (p = 0.029 and p = 0.043, respectively), suggesting enhanced humoral immunity. These findings indicate that RPT may improve immune function in yaks without negatively affecting rumen fermentation or liver health.

The intestinal barrier plays a critical role in maintaining gastrointestinal health and nutrient utilization in yaks. This study investigated the effects of dietary RPG level and RPT supplementation on colonic barrier function and microbial composition in yaks. Twenty-eight healthy male yaks (3 years old; 192.7 ± 4.52 kg) were assigned to a 2 × 2 factorial design with two dietary rumen-protected glucose (RPG) levels (1.0% or 3.0% of dietary DM) and two rumen-protected taurine (RPT) supplementation levels (5 or 20 g/animal/day) for 63 days. High-level RPG impaired colonic physical barrier function by reducing tight junction protein expression and microbial diversity, whereas high-level RPT mainly compromised chemical and immune barrier function by decreasing diamine oxidase activity, mucin-2, and secretory immunoglobulin A, accompanied by alterations in the colonic microbial community. Significant interactions between RPG and RPT were observed for several barrier- and microbiota-related indices. Overall, the effects of RPG and RPT on colonic health were dose-dependent, and moderate supplementation, particularly the combination of 1.0% dietary RPG and 5 g/day RPT, was the most effective in maintaining colonic barrier integrity and microbial homeostasis in yaks.