Álvaro García
Corn silage is a very important feedstuff worldwide, supplying livestock with a consistent supply of a nutrient-dense feed due to its high yield and favorable nutritional profile. The ensiling process involves natural fermentation of water-soluble carbohydrates (WSC) by lactic acid bacteria (LAB), which produce lactic acid to lower the pH and preserve the feed, protecting it from spoilage. However, maintaining high-quality silage is complex and influenced by geography, climate, crop variety, cultivation practices, harvest timing, and processing methods. Temperature and moisture fluctuations during storage can disrupt fermentation, and risk nutrient loss and spoilage. To mitigate these challenges, additives containing the fiber-degrading enzymes cellulase and xylanase have been developed.
Benefits of cellulase and xylanase in corn silage
Cellulase and xylanase are fiber-degrading enzymes that target plant cell walls, breaking down cellulose and hemicellulose to release sugars and fermentable substrates for lactic acid bacteria (LAB) to utilize. These enzymes enhance fiber digestibility, nutrient availability, and silage stability by increasing water-soluble carbohydrates (WSC), which support rapid lactic acid production, stabilize pH, and reduce ammonia nitrogen. This enzymatic process results in silage that is richer in fermentable sugars, more digestible, and less prone to nutrient loss, promoting overall feed stability and palatability.
Enzyme efficacy, however, can vary with forage type and environmental conditions. Cellulase effectiveness does not always correlate directly with dosage, suggesting that its optimal concentration may differ across forages. Likewise, results from combining fiber-degrading enzymes with LAB inoculants have been mixed, likely due to differences in plant structure, initial microbial load, and enzymes ratios and concentration. Further research is needed to refine cellulase and xylanase applications in various forages, including corn silage, focusing on ideal enzyme dosages, LAB combinations, and harvest timing to achieve consistent, high-quality results.
A recent experiment (Li et al., 2023) explored the effects of cellulase and xylanase on corn silage, assessing fermentation and nutrient composition. Corn silage harvested at the dough stage was chopped to 1–3 cm, ensiled, and inoculated with different concentrations of cellulase (10,000 U/g) and xylanase (100,000 U/g) in the following treatments:
- No enzymes added (control)
- Cellulase at 0, 0.25, 0.5, 1.0 g/kg
- Xylanase at 0, 0.25, 0.5, 1.0 g/kg
- Blends of cellulase and xylanase at varying rates
After allowing 60 days of fermentation, all silages were opened and sampled for pH and nutrient composition.
Experimental results
Upon opening the silages, all samples displayed a pH below 4, confirming effective preservation and acidification. This low pH suggests a stable environment that inhibits spoilage organisms, ensuring silages remain well-preserved throughout storage. Silages that were inoculated with cellulase increased their WSC concentration by 7.95% and 23.5% with cellulase at 0.25 g/kg and 0.5 g/kg, respectively, supplying LAB with energy and supporting acidification. Increasing cellulase concentration to 0.25, 0.5, and 1.0 g/kg raised lactic acid levels by 22.5%, 30.1%, and 31.2%, respectively, while simultaneously reducing propionic acid at each concentration level. This shift from propionic to stronger lactic acid enhanced silage stability and nutritional value, as lactic acid more effectively lowers pH and enhances preservation.
Adding xylanase at 0.25 and 0.5 g/kg increased crude protein (CP) by 10.02% and 14.26%, respectively, enhancing protein preservation and nutritional quality. Higher CP improves feed efficiency, supporting livestock growth and productivity. Ether extract (EE) content also rose in both cellulase and xylanase treatments, with cellulase yielding EE increases of 8.75%, 24.24%, and 11.11% at 0.25, 0.5, and 1.0 g/kg, respectively, benefiting animals needing energy-dense diets.
The CP increase with xylanase can be attributed to improved protein preservation during ensiling. Xylanase breaks down hemicellulose in plant cell walls, releasing fermentable sugars that fuel lactic acid bacteria (LAB) activity. This enhanced fermentation accelerates acid production, lowering silage pH more quickly and creating conditions that inhibit proteolytic bacteria and enzymes that would otherwise degrade proteins. By stabilizing pH faster, xylanase helps retain more of the original protein in the forage. Additionally, breaking down cell walls may expose more nitrogen compounds, effectively increasing measurable CP. Together, these effects result in higher CP levels in xylanase-treated silages, enhancing the silage’s nutritional value for ruminants.
Cellulase reduced both NDF and ADF, improving fiber digestibility by breaking down plant fibers, making nutrients more accessible for digestion. This reduction in NDF, potentially linked to increased WSC, indicates enhanced carbohydrate availability and digestibility, making the silage a more efficient feed source for ruminants. Lower NDF in xylanase-treated silages suggests effective fiber breakdown, improving digestibility and potentially increasing feed intake and energy utilization, critical for improved animal performance. The lack of significant ADF reduction is explained because xylanase primarily impacts hemicellulose (which is part of NDF) rather than the more resistant lignin or cellulose, selectively enhancing the digestibility of easier-to-break-down fibers.
In conclusion, the study by Li et al. (2023) demonstrates that cellulase and xylanase additives significantly enhance corn silage’s fermentation quality and nutritional value. Cellulase increased lactic acid, WSC, CP, and EE, while reducing ammonia nitrogen, total nitrogen, NDF, and ADF. Xylanase inhibited acetic and propionic acid production while boosting CP and EE. These findings underscore the importance of selecting forage inoculants with the right concentration of enzyme activity. Optimal silage quality was achieved with 0.5 g/kg cellulase alone or in combination with 0.25 g/kg xylanase, highlighting the value of enzyme levels tailored to enhance nutrient preservation effectively. Including lactobacilli in inoculants could further support fermentation, as these bacteria can utilize the cell contents released by fiber-degrading enzymes, increasing lactic acid production and stabilizing silage pH. Together, this strategic selection of enzyme concentrations and LAB could maximize fermentation benefits, producing stable, nutrient-rich silage.
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