A Comparative Study of Cutting Height and Fermentation Method on Cenchrus fungigraminus Silage: Effects of Natural Fermentation Versus Microbial Inoculant on Silage Quality and Fiber Degradation

Cenchrus fungigraminus (Juncao) is a high-yielding, fast-growing forage crop with considerable potential for livestock feed; however, optimizing its processing is essential for cost reduction and quality enhancement. This study comprised three components: (1) a comprehensive analysis of 25 on-farm silage samples from five locations in Southwest China using Grey Relational Analysis (GRA); (2) an assessment of the effects of three cutting heights (low: 100–150 cm; mid: 150–200 cm; high: 200–250 cm) on silage quality; and (3) a comparison of silage quality between natural fermentation and microbial inoculant treatments using mature Juncao (250–300 cm). The results showed that: (1) in the on-farm silage samples, carbon supplementation was significantly positively correlated with total digestible nutrients (TDN), relative feed value (RFV), ether extract (EE), and sensory evaluation (p < 0.05), and the GRA identified the top-ranked treatments, including J2, J3, J6, X6, and J5; (2) in the cutting height trials, fiber content increased significantly with cutting height (p < 0.05), while crude protein (CP) and TDN decreased significantly (p < 0.05). The 200–250 cm group exhibited optimal fermentation quality, characterized by the highest total volatile fatty acids (total VFA) and lactic acid concentrations, alongside the lowest pH and ammonia nitrogen/total nitrogen ratios (NH3-N/TN); (3) in the inoculant comparison, the natural fermentation group demonstrated significantly higher degradation rates of acid detergent fiber (ADF), neutral detergent fiber (NDF), and acid detergent lignin (ADL) compared to the microbial inoculant group, while also maintaining a lower pH, higher total VFA and lactic acid. Consequently, for on-farm production, carbon supplementation is recommended to improve silage quality. Although cutting Juncao below 200 cm provides higher nutritional value, a height of 200–250 cm is advised to ensure optimal fermentation characteristics. Furthermore, natural fermentation proves superior to microbial inoculant treatment for mature Juncao. Together, these measures offer an effective strategy for producing high-quality Juncao silage.