Roughage plays a pivotal role in mutton sheep production systems, as high-quality roughage resources provide abundant nutrients to enhance growth performance and ensure healthy development. Roughages typically constitute 20–60% of ruminant diets, and their characteristics and costs are critical determinants of production performance, product quality, and profitability in livestock farming (Yi et al., 2022; Patra, 2012). However, the escalating demand for intensive animal production has exacerbated shortages of premium roughage resources, posing a significant constraint to sustainable livestock industry development. Current livestock production systems employ three primary strategies to secure high-quality roughage: (1) utilization of fermented crop straw (Adesogan et al., 2019), (2) increased integration of whole-plant corn silage (Ferraretto et al., 2018), and (3) incorporation of agricultural byproducts (e.g., distillers' grains) as alternative feed ingredients (Niroula et al., 2019). Nevertheless, these approaches face inherent limitations: fermented straw retains high lignin concentrations, large-scale corn silage production may intensify competition between human and livestock feed resources, and the supply of agricultural byproducts such as distillers' grains often proves inconsistent.

In comparison, hydroponic wheat seedlings (HWS) provide 15.83% crude protein and 4.74% crude fat on a dry matter basis, with only 2.3% lignin content. Its tender and succulent stems and leaves ensure high digestibility, making it an ideal green forage (Sneath and Mcintosh, 2003). This system offers three key advantages: (1) year-round sustainable production, (2) conservation of arable land and water resources, and (3) an environmentally friendly production process with reduced labor requirements (Kkalandarov and Abdullaeva, 2022). While HWS represents an excellent strategy for high-quality roughage provision, its utilization requires careful consideration of production needs and economic returns due to its high moisture content (≥80%) and elevated production costs (dry matter conversion costs significantly exceed those of conventional forages like alfalfa).

During hydroponic cultivation, starch and DM content decline progressively, while protein and lipid synthesis increase, enriching energy substrates for livestock (Chavan and Kadam, 1989). HWS has elevated concentrations of vitamin C, α-tocopherol, γ-tocopherol, β-carotene, and ferulic acid compared to traditional roughage (Yang et al., 2001). Germination of wheat seeds enhances the content of antioxidant compounds, such as vitamins, flavonoids, and phenolic acids in seedlings. By optimizing sprouting duration, the contents of riboflavin, α-tocopherol, and total phenolics can be amplified, thereby strengthening free radical scavenging capacity in herbivores—a critical strategy for maintaining livestock health and productivity (Wang et al., 2024). Studies have demonstrated the efficacy of HWS in enhancing production. During the 30-day feeding trial, supplementation with HWS on a dry matter (DM)-matched basis significantly improved average daily gain in sheep compared to traditional feeding regimens (Gebremedhin et al., 2015). During the 36-day feeding trial, dietary supplementation with 5–15% hydroponic barley seedlings significantly increased total milk protein content, antioxidant activity, and milk fat percentage in lactating ewes. However, at a 20% inclusion level, both milk antioxidant activity and fat content showed reductions (Ma et al., 2024). During the 8-week feeding period, inclusion of 25% HWS in Holstein dairy rations significantly elevated dry matter (DM) intake, average daily gain, milk yield, and milk fat percentage compared to the control group (Bari et al., 2020). Furthermore, an 8-week feeding trial revealed that inclusion of 25% hydroponic barley seedlings in the diet showed no significant effects on feed intake or body weight in Holstein heifers. However, at a 50% inclusion level, significant reductions were observed in both feed intake and body weight, along with decreased apparent digestibility of crude protein and organic matter (Ren et al., 2022). Additional studies revealed that during a 3-week experimental period, replacing 10% of conventional TMR with either hydroponic barley seedlings or HWS improved production efficiency in dairy cows. The hydroponic barley seedlings group achieved the highest feed-to-milk conversion ratio, while the HWS group demonstrated superior body weight gain. Furthermore, the HWS group showed significantly greater apparent digestibility of organic matter, crude protein, and starch compared to both the hydroponic barley seedlings and conventional TMR groups (Zang et al., 2024). Additionally, HWS offers an economic advantage over hydroponic barley seedlings in terms of production cost, as the raw material price of wheat (4.66 CNY/kg) is considerably lower than that of barley (6.72 CNY/kg). Currently, limited information exists regarding the effects of hydroponic wheat seedlings on slaughter performance, rumen fermentation, and microbial community dynamics in finishing Hu sheep. We hypothesize that graded replacement of conventional feed with HWS optimizes rumen function through coordinated restructuring of microbial communities and activation of key metabolic pathways. Therefore, the objective of this study was to evaluate the responses of 4-month-old Hu sheep during the fattening period, while their diets are replaced with different proportions (5–20%) of HWS.

The All animal care and handling procedures in this study were conducted in strict accordance with the Guidelines for the Care and Use of Laboratory Animals in China and were approved and overseen by the Animal Care and Use Committee of Xinjiang Academy of Animal Sciences (Approval No. FRI-2023002; Urumqi, China).

NH₃-N serves as a critical nitrogen source for microbial protein synthesis, directly influencing the ruminal microbial protein utilization efficiency and microbial proliferation dynamics. While ruminal NH₃-N levels typically are positively correlated with dietary protein content and intake, this study revealed significant NH₃-N elevation in the T10, T15, and T20 groups, potentially attributable to HWS's superior protein composition compared to conventional diets (Zhou et al., 2018). The enhanced degradability of hydroponic plant cell walls likely stimulated the fibrolytic activity of rumen bacteria such as Ruminococcus spp., accelerating amino acid deamination and microbial protein synthesis efficiency, thereby modulating ruminal ammonia utilization. Dietary inclusion of HWS increased the fiber content, prolonging rumination duration and enhancing feed-specific microbial adhesion, which synergistically improved microbial protein utilization and NH₃-N production (Min et al., 2024). Notably, although the NH3-N concentration in T20 was higher than in CON, its incremental gain relative to T15 suggests a potential threshold inhibitory effect. This phenomenon may be attributed to excessive alkaloids supplied by the 20% HWS, which could suppress the growth of Butyrivibrio in the rumen, thereby reducing amino acid deamination and subsequent ammonia nitrogen production (Petric et al., 2021). Acetate concentration increased linearly with the percentage of HWS inclusion, likely driven by the higher soluble fiber content in HWS, which preferentially favors fibrolytic bacteria such as Ruminococcus spp. that generate acetate via enhanced carbohydrate fermentation (Jeyanathan et al., 2014). Concurrently, the trend toward a decrease in acetate-to-propionate ratio suggests metabolic pathway shifts, with propionate's relative predominance potentially enhancing hepatic gluconeogenesis—a physiologically advantageous adaptation for ovine energy metabolism.

The ruminal microbial community in ruminants exhibits a complex and diverse structure including bacteria, fungi, and archaea. Bacteria constitute the most functionally significant microbial group in the rumen, with diversity and relative abundance are strongly influenced by diet (Wang et al., 2017). Rumen homeostasis is contingent upon microbial richness and diversity, with high bacterial richness and diversity being recognized as beneficial for enhancing ruminal stability (Weimer, 2015). The Chao1 and ACE indices reflect microbial richness, while the Simpson and Shannon indices characterize community diversity. In this study, no significant differences were observed in ACE, Chao1, Simpson, or Shannon indices across dietary treatments. These findings may be attributed to either the relatively low inclusion level of HWS in the experimental diets or the insufficient adaptation period, both of which might have been inadequate to exceed the response threshold required to alter the core rumen microbiota in ruminants. An important finding of this study was that the beta diversity of the ruminal microbiota, assessed by PCoA, did not exhibit significant separation among dietary groups. This indicates that the overall architecture of the microbial community remained largely resilient to the graded replacement of conventional feed with HWS. This phenomenon could be attributed to the fact that HWS primarily provides highly fermentable nutrients that may stimulate the growth of certain pre-existing, opportunistic taxa within the rumen, without drastically altering the fundamental interactions between broader microbial groups. Therefore, the ecological implications of HWS should be interpreted as a modulation of community membership within a stable structural framework, highlighting the need to focus on specific functional taxa rather than overall community topology when evaluating its impact. The dominant bacterial phyla in the rumen were Bacteroidetes (34.5%) and Firmicutes (55.1%), aligning with previous ruminant studies (Qian et al., 2018). Substitution of 5–20% HWS in the basal diet increased the relative abundance of Firmicutes while reducing Bacteroidetes and Prevotella. Prevotella is the most abundant genus within Bacteroidetes and plays a critical role in protein and carbohydrate degradation, particularly in polysaccharide and proteolytic processes (Kim et al., 2011). Elevated cellulose levels from HWS supplementation mitigated the decline in the relative abundance of Prevotella and stabilized ruminal pH. As expected, the cellulolytic bacteria, including Ruminococcus, Succinivibrio, and Veillonella, were enriched by increasing HWS content in the feed. Ruminococcus primarily degrades cellulose, while Succinivibrio produces succinate as a precursor for propionate and acetate synthesis. Propionate serves as a gluconeogenic substrate, absorbed by rumen epithelial cells as lactate and metabolized in the liver via gluconeogenesis or the tricarboxylic acid cycle. Propionate production via succinate fermentation and pyruvate utilization by Veillonella were correlated with increased propionate concentrations in this study (Van Gylswyk, 1995). Increasing HWS inclusion enhanced the relative abundance of energy-utilizing taxa within Firmicutes, promoting the proliferation of Succinivibrio and Veillonella. The high cellulose content in HWS stimulated robust cellulolytic activity, with fiber degradation by hemicellulases and cellulases, followed by further fermentation to volatile fatty acids, driving elevated propionate production (Abdel-Wareth et al., 2023).

Carcass performance serves as a critical metric for evaluating meat-producing livestock output value, primarily assessed through parameters including carcass weight (CW), dressing percentage, loin eye muscle area, and GR value. CW reflects meat yield and carcass quality, while loin eye muscle area strongly correlates with muscularity, and GR value indicates intramuscular fat deposition. (Sultana et al. 2022) reported that 25–75 g/kg hydroponic wheat seedling supplementation in broiler diets increased pre-slaughter weight, CW, breast muscle yield, and wing weight without affecting dressing percentage. Similarly, (Devendar et al. 2020) observed enhanced pre-slaughter weight and HCW in goats given feed containing 20% hydroponic barley seedlings substitution, though dressing percentage remained unchanged. In our study, 5–20% HWS substitution in a TMR diet elevated pre-slaughter weight and CW in Hu sheep, aligning with these findings. It is worth noting that the 15% and 20% HWS groups exhibited increased loin eye muscle area, potentially attributable to the high digestibility of HWS and the resulting optimal rumen fermentation. This improvement in the rumen microenvironment enhances production of propionate and other volatile fatty acids, thereby providing valuable energy substrates for muscle growth and reducing protein catabolism (Bergman, 1990).

Water-holding capacity (WHC), defined as muscle tissue's ability to retain intrinsic moisture under mechanical, thermal, or storage stress, is routinely assessed through drip loss and cooked meat percentage—critical parameters for evaluating meat processing suitability and shelf-life (Warner, 2017). In this study, 10% and 15% HWS substitution significantly reduced longissimus dorsi water loss rate, while all HWS groups exhibited elevated cooked meat percentage. These effects may stem from HWS-enhanced protein digestibility, which promotes nitrogen retention, increased myofibrillar protein content, and enhanced water-binding capacity via collagen-myoprotein interactions. The heat-induced protein denaturation during cooking can also form a hydrated matrix that preserves moisture, enhancing juiciness and flavor, key determinants of consumer preference in meat quality (Ebeid et al., 2022). This phenomenon may also be attributed to alterations in dietary starch composition resulting from HWS substitution, which could influence cellular energy supply pathways and consequently affect cellular water transport capacity (Boukrouh et al., 2024). The variation in cooked meat percentage may be associated with flavonoids in HWS, which influence the permeability of muscle cell membranes, allowing calcium ions to infiltrate the cells, thereby reducing glycolytic efficiency and making muscle proteins more prone to denaturation during boiling, consequently affecting cooked meat percentage (Li et al., 2025). Inosine monophosphate (IMP), a nucleotide metabolite and key umami compound, contributes to meat flavor through Maillard reaction-derived volatile aromatics; the level of its degradation products (e.g., hypoxanthine) directly correlates with a greater sense of palatability (Belloir et al., 2025). The longissimus dorsi muscle in the 20% HWS group exhibited significantly reduced IMP content, which attenuated umami intensity (characterized by savory, broth-like flavor profiles). Concurrently, hypoxanthine accumulation may have contributed to increased bitter off-flavors, a phenomenon that could be associated with post-slaughter pH changes. We propose a hypothetical pathway based on the established literature: during rigor mortis progression (ATP → ADP → AMP → IMP → inosine), a potentially lower ultimate muscle pH in sheep fed 20% HWS might have created a weakly acidic environment that destabilizes IMP. This could theoretically accelerate its enzymatic hydrolysis by phosphomonoesterase into inosine and subsequent breakdown to hypoxanthine and ribose via nucleoside hydrolases—a catabolic cascade known to be pH-dependent, which would limit IMP retention (Kanokruangrong et al., 2025). If this proposed pathway holds true, the degradation of IMP would attenuate umami intensity (typically manifested as savory, broth-like flavors), while simultaneously increasing the potential for an undesirable bitter taste due to hypoxanthine accumulation. However, this specific mechanistic cascade remains to be directly validated in future studies.

Lamb meat is valued as a high-protein, low-fat animal product with a distinctive flavor, largely deriving its nutritional and sensory qualities from its composition of amino acids and fatty acids (Ma et al., 2020). While 5–20% HWS substitution in the basal diet did not significantly alter amino acid profiles in longissimus dorsi, the numerical increases in Gly, Ser, Thr, Ile, Asp, Met, Tyr, and SEAA suggest sub-threshold modulation of amino acid metabolism. This is likely due to the highly conserved nature of muscle protein structure, which is genetically determined. In ruminants, the extensive modification of dietary protein by rumen microbes results in a relatively consistent post-ruminal supply of amino acids, unless the diet induces a major microbial shift. The improvements from HWS supplementation therefore appear to have been driven by enhanced nutrient availability and ruminal efficiency, which supported greater overall protein deposition without altering the fundamental amino acid profile of the deposited tissue. UFAs, prone to oxidative degradation, generate volatile aldehydes, ketones, and alcohols that contribute to lamb's characteristic ‘gamey' flavor, whereas SFAs with higher melting points enhance succulence through thermal stabilization during cooking (Saengsuk et al., 2024). Heptadecanoic acid (C17:0), an odd-chain SFA serving as both a meat quality biomarker and flavor modulator in ruminant adipose tissues (Munezero et al., 2024), was significantly elevated in HWS-fed lambs. This increase not only enhanced meat flavor characteristics but also improved lipid metabolism. Furthermore, long-term consumption of C17:0-enriched products may confer cardiovascular disease risk reduction benefits to consumers. This C17:0 accumulation may stem from bioactive, HWS-derived amino acids that affect propionate metabolism. As an odd-chain fatty acid, C17:0 deposition is tightly regulated by ruminal propionate flux—a process potentiated in T15 sheep by markedly elevated NH₃-N concentrations, indicative of enhanced microbial deamination. Proliferation of ammoniagenic bacteria such as Clostridium glutamicum, likely accelerated α-ketoglutarate release into the tricarboxylic acid (TCA) cycle, stimulating propionate synthesis (Halarnkar and Blomquist, 1989). However, there is a lack of direct experimental evidence for transcriptomic or metabolomic analysis. This may provide a new idea for the future verification of key metabolic pathways in rumen and host tissues through multi-omics technology. Hepatic gluconeogenic conversion of propionate to glucose, coupled with its role as a methylmalonyl-CoA precursor for odd-chain fatty acid elongation, correlates with T0′s C17:0 peak. However, HWS substitution >10% linearly increased acetate production, altering the acetate/propionate ratio to suppress propionate-dependent Prevotellaceae_UCG_001 activity while activating acetate-generating fibrolytic taxa, like Ruminococcus flavefaciens, thereby reducing C17:0 synthesis (Zhang et al., 2017). The quadratic response of PUFA content to HWS inclusion may reflect polyphenol-mediated rumen microbial modulation. Ferulic acid and vitamin E in HWS likely protected cis-double bonds in α-linolenic acid (C18:3n-3) from biohydrogenation by inhibiting hydrolases of Butyrivibrio proteoclasticus (Banakar et al., 2023). Concurrently, Bacteroidetes-enhanced polysaccharide degradation increases short-chain fatty acid (SCFA) production, upregulating fatty acid-binding protein 2 expression to improve PUFA absorption (Li et al., 2023). Fiber-derived metabolites from the Rikenellaceae_RC9_gut_group may further activate peroxisome proliferator-activated receptor alpha, promoting PUFA transport into muscle (Mao et al., 2025). With 15–20% HWS, prolonged digesta retention could activate Desulfobacterota-mediated sulfate reduction, and generate hydrogen sulfide that would inhibit mitochondrial β-oxidation and PUFA translocation (Liu et al., 2024). Simultaneously, Firmicutes-enriched microbiota likely enhanced stearoyl-CoA desaturase activity, converting C18:3n-3 to stearic acid (C18:0), a process compounded by Proteobacteria-associated biohydrogenation, collectively driving the quadratic decline in PUFA deposition.

This study demonstrates that a 15% replacement of conventional feed with hydroponic wheat seedlings in Hu sheep diets optimizes slaughter performance and economic returns, while higher substitution rates (20%) negatively impact these parameters and impair inosine monophosphate synthesis in meat. Rumen fermentation profiles and slaughter indices indicate hydroponic wheat seedlings supplementation enhances nitrogen utilization efficiency and growth performance in finishing Hu sheep, with the increased Prevotellaceae_UCG-001 abundance suggesting improved heptadecanoic acid synthesis in longissimus dorsi muscle through rumen microbial metabolic functions. The elevated pre-slaughter live weights and reduced Butyrivibrio and Saccharofermentans abundances further support enhanced feed efficiency. We recommend 15% hydroponic wheat seedlings inclusion as an optimal feeding strategy for finishing Hu sheep, offering potential benefits including increased production yield, reduced feeding costs, and alleviated human-livestock feed competition. This approach shows particular promise for implementation in cold regions, seasonally water-scarce areas, and intensive commercial farming systems to reduce land and water resource dependence.