Background <p>Low-carbon feeding is an effective strategy to reduce nutrient losses and environmental emissions in swine production. High-protein (HP) diets increase nitrogen (N) excretion and ammonia (NH₃) emissions, whereas low-protein (LP) diets improve N utilization but may impair growth performance. Silicate (SIL) has been reported to enhance digestion and reduce harmful gas emissions; however, its efficacy under different dietary protein levels remains unclear. Therefore, this study evaluated the effects of SIL supplementation in HP and LP diets to provide evidence for efficient and low-carbon pig production.</p> Methods <p>A 10-wk feeding trial was conducted using 200 pigs [Duroc × (Landrace × Yorkshire)] with an initial body weight of 55.40 ± 3.36&#xa0;kg. Pigs were randomly assigned to four dietary treatments in a randomized complete block design, with 10 replicates per treatment and 5 pigs per pen (2 gilts and 3 barrows). The experiment followed a 2 × 2 factorial arrangement, consisting of two dietary protein levels: HP and LP diets, with 2% lower crude protein (CP), and two levels of SIL supplementation (0 or 0.1%).</p> Results <p>The results demonstrated that dietary supplementation with 0.1% SIL significantly improved growth performance, as indicated by increased average daily gain (ADG) and reduced feed conversion ratio (FCR) (<i>P</i><i> &lt; 0.05</i>). SIL supplementation also enhanced the digestibility of dry matter (DM), N, and energy (E), while reducing moisture digestibility (<i>P</i> &lt; 0.05). In addition, SIL significantly decreased fecal emissions of NH₃, hydrogen sulfide (H₂S), and carbon dioxide (CO₂) and improved fecal consistency scores at wk 10 (<i>P</i> &lt; 0.05), indicating its potential to mitigate environmental emissions. Regarding physiological responses, SIL supplementation increased white blood cell (WBC) counts and blood glucose concentrations (<i>P</i> &lt; 0.05 and <i>P</i> &lt; 0.01, respectively), while reducing serum creatinine and cortisol levels (<i>P</i> &lt; 0.05), suggesting improved metabolic status and reduced physiological stress. In terms of meat quality, SIL enhanced muscle water-holding capacity (WHC), reduced drip loss, and improved tissue cohesiveness and elasticity (<i>P</i> &lt; 0.05). Moreover, SIL supplementation increased the proportion of unsaturated fatty acids and improved the ratio of saturated to unsaturated fatty acids, indicating a favorable modification of lipid composition. Dietary protein level also exerted significant main effects. LP diets reduced CO₂ emissions and blood urea nitrogen (BUN) concentrations (<i>P</i> &lt; 0.05), reflecting a lower N metabolic burden and reduced carbon emissions. No significant interaction between dietary protein level and SIL supplementation was observed for the measured parameters. Fecal microbiota analysis showed that SIL supplementation was associated with alterations in gut microbial composition, characterized by an increased relative abundance of beneficial taxa, including Lactobacillus and members of the Lactobacillaceae family. These microbial shifts may contribute to improved intestinal health and more favorable fermentation characteristics, thereby supporting the observed reductions in harmful gas emissions.</p> Conclusion <p>Dietary inclusion of 0.1% SIL represents an effective nutritional strategy for enhancing growth performance and nutrient utilization in finishing pigs, while supporting a low-carbon feeding model. By improving gut health and reducing environmental emissions, SIL demonstrates strong potential as a functional feed additive for promoting both productivity and environmental sustainability in pig production.</p>