Álvaro García
Microbial inoculants, which introduce beneficial bacteria and enzymes, have emerged as a crucial solution for maintaining and enhancing the quality of legume-grass silage and other types of silages. By promoting efficient fermentation and preserving essential nutrients, these inoculants ensure that the forage retains its nutritional value throughout the storage period. The combination of various beneficial microorganisms and enzymes can optimize the fermentation process, inhibit spoilage organisms, and improve overall silage stability.
In the U.S., forage cocktail mixes—blends of grasses, legumes, and other forage plants—have become increasingly popular for improving livestock feed quality and soil health. These mixes often include species like alfalfa, clover, and ryegrass, each selected for their specific benefits, such as high protein content or soil fertility enhancement. However, to attain the maximum nutritional advantages of these forage blends, preserving them adequately during storage through proper fermentation is critical.
Recent research
A recent experiment conducted at the Chinese Laboratory of Forage Cultivation (Quiang et al. 2023) tested combining Lactiplantibacillus plantarum and cellulase to enhance the quality of silage made from alfalfa and ryegrass. This study examined the effects on fermentation and nutrient preservation, providing practical insights for optimizing forage blends. These findings can help farmers enhance the efficiency and sustainability of their forage management practices, ensuring better feed quality and reduced nutrient loss.
In this study, the forage blend, consisting of a 3:2 ratio of alfalfa to ryegrass by weight, was treated with the following:
- An untreated control with no additives
- Lactiplantibacillus plantarum (1 × 10^6 cfu/g fresh material (FM))
- Cellulase (7.5 × 10^2 U/kg FM)
- A combination of 2 and 3.
Silage treated with Lactiplantibacillus plantarum, cellulase, and their combination had significantly lower pH compared to the control, indicating better acidification for preservation. Cellulase caused the most notable pH drop by Day 5, accelerating early acidification. All treatments had higher lactic acid concentrations than the control, with cellulase showing a sharp rise by Day 5 and the Lactiplantibacillus-cellulase combination achieving the highest concentrations by the end of fermentation. Acetic acid was initially higher in the control but increased more in treated silages over time. No propionic or butyric acids were detected. All three treatments had lower ammonia nitrogen levels, reflecting improved protein preservation. Water-soluble carbohydrates, essential for fermentation as they fuel beneficial bacteria, decreased over time as they were converted into acids like lactic acid, improving silage quality and preservation. This reduction is typical of the fermentation process. Treated silages showed a faster decrease in water-soluble carbohydrates by Day 5, while the control silage had significantly lower water-soluble carbohydrates concentrations by the end of fermentation.
Chemical composition of the silages
There were no significant differences in the amount of acid detergent fiber (ADF) among the various treatments. Acid detergent fiber is a measure of the more indigestible fiber in silage, and its concentrations were similar across all treatments, indicating that the treatments did not affect its content. However, the silage treated with the Lactiplantibacillus-cellulase combination had lower neutral detergent fiber (NDF) and hemicellulose compared to the other treatments. Neutral detergent fiber includes all types of fiber and is an indicator of the total fiber content in the silage, while hemicellulose is a component of NDF that can be broken down by enzymes. Lower NDF and hemicellulose in the Lactiplantibacillus-cellulase combination silage suggest both additives together effectively reduced these fiber components, likely due to the cellulase breaking down the fibrous materials.
Additionally, the Lactiplantibacillus-cellulase combination silage showed the best dry matter recovery, meaning it retained more of its original dry matter content compared to other treatments. This indicates that the combined treatment not only improved the fiber quality but also minimized losses during fermentation, resulting in better overall preservation of the silage.
Microbial communities in the silages
On Day 5, the control silage had a more diverse bacterial community compared to the treated silages, reflecting a broader range of bacteria at this early stage. By Day 30, however, the silage treated with Lactiplantibacillus showed the least diversity, with this bacterium becoming the dominant genus. This shift indicates that inoculation with Lactiplantibacillus, especially in combination with cellulase, effectively promoted Lactiplantibacillus populations. This is beneficial for silage because Lactiplantibacillus produces more lactic acid, which lowers pH and enhances preservation.
Initially, both the control and cellulase-treated silages had higher concentrations of Klebsiella. However, by Day 30, Lactiplantibacillus had outnumbered Klebsiella, suggesting improved fermentation conditions. Cellulase also increased Weissella in cellulase-inoculated silage. This bacterium is especially useful in the early stages of fermentation as it helps initiate acidification. Although its levels typically decline as Lactobacillus becomes more dominant, Weissella’s early contribution is crucial for setting the stage for successful fermentation and preservation.
The combination of Lactiplantibacillus plantarum and cellulase resulted in the lowest pH and highest lactic acid content, signifying improved fermentation. Cellulase alone also effectively increased lactic acid and reduced pH. Early acetic acid concentrations were low, and no propionic acid was produced due to the low pH. Treated silages preserved water-soluble carbohydrates better and experienced less nutrient loss compared to the control. Additives enhanced Lactiplantibacillus growth and suppressed undesirable bacteria.
Bacterial metabolic functions shifted during ensiling, with Lactiplantibacillus and cellulase treatment enhancing carbohydrate and energy metabolism and reducing ammonia nitrogen concentrations, indicating better protein preservation. The combined effects of Lactiplantibacillus plantarum and cellulase led to more efficient fermentation.
Practical implications
This study highlights the significant benefits of using Lactiplantibacillus plantarum and cellulase as microbial inoculants for enhancing the quality of legume-grass silage. The combination of these additives resulted in lower pH, higher lactic acid content, and better protein preservation, indicating improved fermentation and silage stability. The treated silages showed a faster reduction in water-soluble carbohydrates, less nutrient loss, and more effective suppression of undesirable bacteria compared to the control. Improved microbial community dynamics and enhanced metabolic functions further contributed to the superior quality of the silage.
For livestock producers, incorporating Lactiplantibacillus plantarum and cellulase into silage management practices offers a practical and effective solution to improve feed quality, particularly for high-protein forages like those containing legumes. Future research should continue to explore the long-term impacts of these additives on silage stability, animal health, and performance, as well as investigate other potential additive combinations to further enhance silage quality and preservation. This study provides a foundation for optimizing forage management practices, ensuring better feed quality and reducing nutrient loss in various silage types.
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